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Date: Wed, 03 May 2017 14:13:58 -0400
From: Jeff Layton <jlayton@...chiereds.net>
To: David Howells <dhowells@...hat.com>, viro@...iv.linux.org.uk
Cc: linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
linux-kernel@...r.kernel.org, mszeredi@...hat.com
Subject: Re: [PATCH 3/9] VFS: Introduce a mount context
On Wed, 2017-05-03 at 17:04 +0100, David Howells wrote:
> Introduce a mount context concept. This is allocated at the beginning of
> the mount procedure and into it is placed:
>
> (1) Filesystem type.
>
> (2) Namespaces.
>
> (3) Device name.
>
> (4) Superblock flags (MS_*) and mount flags (MNT_*).
>
> (5) Security details.
>
> (6) Filesystem-specific data, as set by the mount options.
>
> It also gives a place in which to hang an error message for later retrieval
> (see the mount-by-fd syscall later in this series).
>
> Rather than calling fs_type->mount(), a mount_context struct is created and
> fs_type->fsopen() is called to set it up. fs_type->mc_size says how much
> should be added on to the mount context for the filesystem's use.
>
> A set of operations have to be set by ->fsopen() to provide freeing,
> duplication, option parsing, binary data parsing, validation, mounting and
> superblock filling.
>
> It should be noted that, whilst this patch adds a lot of lines of code,
> there is quite a bit of duplication with existing code that can be
> eliminated should all filesystems be converted over.
>
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---
>
> Documentation/filesystems/mounting.txt | 445 ++++++++++++++++++++++++++++++++
> fs/Makefile | 3
> fs/internal.h | 2
> fs/mount.h | 3
> fs/mount_context.c | 343 +++++++++++++++++++++++++
> fs/namespace.c | 270 +++++++++++++++++--
> fs/super.c | 50 +++-
> include/linux/fs.h | 11 +
> include/linux/lsm_hooks.h | 37 +++
> include/linux/mount.h | 67 +++++
> include/linux/security.h | 29 ++
> security/security.c | 32 ++
> security/selinux/hooks.c | 179 +++++++++++++
> 13 files changed, 1435 insertions(+), 36 deletions(-)
> create mode 100644 Documentation/filesystems/mounting.txt
> create mode 100644 fs/mount_context.c
>
> diff --git a/Documentation/filesystems/mounting.txt b/Documentation/filesystems/mounting.txt
> new file mode 100644
> index 000000000000..a942ccd08376
> --- /dev/null
> +++ b/Documentation/filesystems/mounting.txt
> @@ -0,0 +1,445 @@
> + ===================
> + FILESYSTEM MOUNTING
> + ===================
> +
> +CONTENTS
> +
> + (1) Overview.
> +
> + (2) The mount context.
> +
> + (3) The mount context operations.
> +
> + (4) Mount context security.
> +
> + (5) VFS mount context operations.
> +
> +
> +========
> +OVERVIEW
> +========
> +
> +The creation of new mounts is now to be done in a multistep process:
> +
> + (1) Create a mount context.
> +
> + (2) Parse the options and attach them to the mount context. Options may be
> + passed individually from userspace.
> +
> + (3) Validate and pre-process the mount context.
> +
> + (4) Perform the mount.
> +
> + (5) Return an error message attached to the mount context.
> +
> + (6) Destroy the mount context.
> +
> +To support this, the file_system_type struct gains two new fields:
> +
> + unsigned short mc_size;
> +
> +which indicates how much space the filesystem would like tacked onto the end of
> +the mount_context struct for its own purposes, and:
> +
> + int (*fsopen)(struct mount_context *mc, struct super_block *src_sb);
> +
> +which is invoked to set up the filesystem-specific parts of a mount context,
> +including the additional space. The src_sb parameter is used to convey the
> +superblock from which the filesystem may draw extra information (such as
> +namespaces), for submount (MS_SUBMOUNT) or remount (MS_REMOUNT) purposes or it
> +will be NULL.
> +
> +Note that security initialisation is done *after* the filesystem is called so
> +that the namespaces may be adjusted first.
> +
> +And the super_operations struct gains one:
> +
> + int (*remount_fs_mc) (struct super_block *, struct mount_context *);
> +
> +This shadows the ->remount_fs() operation and takes a prepared mount context
> +instead of the mount flags and data page. It may modify the ms_flags in the
> +context for the caller to pick up.
> +
> +[NOTE] remount_fs_mc is intended as a replacement for remount_fs.
> +
> +
> +=================
> +THE MOUNT CONTEXT
> +=================
> +
> +The mount process is governed by a mount context. This is represented by the
> +mount_context structure:
> +
> + struct mount_context {
> + const struct mount_context_operations *ops;
> + struct file_system_type *fs;
> + struct user_namespace *user_ns;
> + struct mnt_namespace *mnt_ns;
> + struct pid_namespace *pid_ns;
> + struct net *net_ns;
> + const struct cred *cred;
> + char *device;
> + char *root_path;
> + void *security;
> + const char *error;
> + unsigned int ms_flags;
> + unsigned int mnt_flags;
> + bool mounted;
> + bool sloppy;
> + bool silent;
> + enum mount_type mount_type : 8;
> + };
> +
> +When allocated, the mount_context struct is extended by ->mc_size bytes as
> +specified by the specified file_system_type struct. This is for use by the
> +filesystem. The filesystem should wrap the struct in its own, e.g.:
> +
> + struct nfs_mount_context {
> + struct mount_context mc;
> + ...
> + };
> +
> +placing the mount_context struct first. container_of() can then be used.
> +
> +The mount_context fields are as follows:
> +
> + (*) const struct mount_context_operations *ops
> +
> + These are operations that can be done on a mount context. See below.
> + This must be set by the ->fsopen() file_system_type operation.
> +
> + (*) struct file_system_type *fs
> +
> + A pointer to the file_system_type of the filesystem that is being
> + mounted. This retains a ref on the type owner.
> +
> + (*) struct user_namespace *user_ns
> + (*) struct mnt_namespace *mnt_ns
> + (*) struct pid_namespace *pid_ns
> + (*) struct net *net_ns
> +
> + This is a subset of the namespaces in use by the invoking process. This
> + retains a ref on each namespace. The subscribed namespaces may be
> + replaced by the filesystem to reflect other sources, such as the parent
> + mount superblock on an automount.
> +
> + (*) struct cred *cred
> +
> + The mounter's credentials. This retains a ref on the credentials.
> +
> + (*) char *device
> +
> + This is the device to be mounted. It may be a block device
> + (e.g. /dev/sda1) or something more exotic, such as the "host:/path" that
> + NFS desires.
> +
> + (*) char *root_path
> +
> + A path to the place inside the filesystem to actually mount. This allows
> + a mount and bind-mount to be combined.
> +
> + [NOTE] This isn't implemented yet, but NFS has the code to do this which
> + could be moved to the VFS.
> +
> + (*) void *security
> +
> + A place for the LSMs to hang their security data for the mount. The
> + relevant security operations are described below.
> +
> + (*) const char *error
> +
> + A place for the VFS and the filesystem to hang an error message. This
> + should be in the form of a static string that doesn't need deallocation
> + and the pointer to which can just be overwritten. Under some
> + circumstances, this can be retrieved by userspace.
> +
> + Note that the existence of the error string is expected to be guaranteed
> + by the reference on the file_system_type object held by ->fs or any
> + filesystem-specific reference held in the filesystem context until the
> + ->free() operation is called.
> +
> + (*) unsigned int ms_flags
> + (*) unsigned int mnt_flags
> +
> + These hold the mount flags. ms_flags holds MS_* flags and mnt_flags holds
> + MNT_* flags.
> +
> + (*) bool mounted
> +
> + This is set to true once a mount attempt is made. This causes an error to
> + be given on subsequent mount attempts with the same context and prevents
> + multiple mount attempts.
> +
> + (*) bool sloppy
> + (*) bool silent
> +
> + These are set if the sloppy or silent mount options are given.
> +
> + [NOTE] sloppy is probably unnecessary when userspace passes over one
> + option at a time since the error can just be ignored if userspace deems it
> + to be unimportant.
> +
> + [NOTE] silent is probably redundant with ms_flags & MS_SILENT.
> +
> + (*) enum mount_type
> +
> + This indicates the type of mount operation. The available values are:
> +
> + MOUNT_TYPE_NEW -- New mount
> + MOUNT_TYPE_SUBMOUNT -- New automatic submount of extant mount
> + MOUNT_TYPE_REMOUNT -- Change an existing mount
> +
> +The mount context is created by calling __vfs_fsopen(), vfs_fsopen(),
> +vfs_mntopen() or vfs_dup_mount_context() and is destroyed with
> +put_mount_context(). Note that the structure is not refcounted.
> +
> +VFS, security and filesystem mount options are set individually with
> +vfs_mount_option() or in bulk with generic_monolithic_mount_data().
> +
> +When mounting, the filesystem is allowed to take data from any of the pointers
> +and attach it to the superblock (or whatever), provided it clears the pointer
> +in the mount context.
> +
> +The filesystem is also allowed to allocate resources and pin them with the
> +mount context. For instance, NFS might pin the appropriate protocol version
> +module.
> +
> +
> +============================
> +THE MOUNT CONTEXT OPERATIONS
> +============================
> +
> +The mount context points to a table of operations:
> +
> + struct mount_context_operations {
> + void (*free)(struct mount_context *mc);
> + int (*dup)(struct mount_context *mc, struct mount_context *src);
> + int (*option)(struct mount_context *mc, char *p);
> + int (*monolithic_mount_data)(struct mount_context *mc, void *data);
> + int (*validate)(struct mount_context *mc);
> + struct dentry *(*mount)(struct mount_context *mc);
> + int (*fill_super)(struct super_block *s, struct mount_context *mc);
> + };
> +
> +These operations are invoked by the various stages of the mount procedure to
> +manage the mount context. They are as follows:
> +
> + (*) void (*free)(struct mount_context *mc);
> +
> + Called to clean up the filesystem-specific part of the mount context when
> + the context is destroyed. It should be aware that parts of the context
> + may have been removed and NULL'd out by ->mount().
> +
> + (*) int (*dup)(struct mount_context *mc, struct mount_context *src);
> +
> + Called when a mount context has been duplicated to get any refs or copy
> + any non-referenced resources held in the filesystem-specific part of the
> + mount context. An error may be returned to indicate failure to do this.
> +
> + [!] Note that if this fails, put_mount_context() will be called
> + immediately thereafter, so ->dup() *must* make the
> + filesystem-specific part safe for ->free().
> +
> + (*) int (*option)(struct mount_context *mc, char *p);
> +
> + Called when an option is to be added to the mount context. p points to
> + the option string, likely in "key[=val]" format. VFS-specific options
> + will have been weeded out and mc->ms_flags and mc->mnt_flags updated in
> + the context. Security options will also have been weeded out and
> + mc->security updated.
> +
> + If successful, 0 should be returned and a negative error code otherwise.
> + If an ambiguous error (such as -EINVAL) is returned, mc->error should be
> + set in the context to a string that provides more information.
> +
> + (*) int (*monolithic_mount_data)(struct mount_context *mc, void *data);
> +
> + Called when the mount(2) system call is invoked to pass the entire data
> + page in one go. If this is expected to be just a list of "key[=val]"
> + items separated by commas, then this may be set to NULL.
> +
> + The return value is as for ->option().
> +
> + If the filesystem (eg. NFS) needs to examine the data first and then
> + finds it's the standard key-val list then it may pass it off to:
> +
> + int generic_monolithic_mount_data(struct mount_context *mc, void *data);
> +
> + (*) int (*validate)(struct mount_context *mc);
> +
> + Called when all the options have been applied and the mount is about to
> + take place. It is should check for inconsistencies from mount options
> + and it is also allowed to do preliminary resource acquisition. For
> + instance, the core NFS module could load the NFS protocol module here.
> +
> + Note that if mc->mount_type == MOUNT_TYPE_REMOUNT, some of the options
> + necessary for a new mount may not be set.
> +
> + The return value is as for ->option().
> +
> + (*) struct dentry *(*mount)(struct mount_context *mc);
> +
> + Called to effect a new mount or new submount using the information stored
> + in the mount context (remounts go via a different vector). It may detach
> + any resources it desires from the mount context and transfer them to the
> + superblock it creates.
> +
> + On success it should return the dentry that's at the root of the mount.
> + In future, mc->root_path will then be applied to this.
> +
> + In the case of an error, it should return a negative error code and set
> + mc->error.
> +
> + (*) int (*fill_super)(struct super_block *s, struct mount_context *mc);
> +
> + This is available to be used by things like mount_ns_mc() that are called
> + by ->mount() to transfer information/resources from the mount context to
> + the superblock.
> +
> +
> +======================
> +MOUNT CONTEXT SECURITY
> +======================
> +
> +The mount context contains a security points that the LSMs can use for
> +building up a security context for the superblock to be mounted. There are a
> +number of operations used by the new mount code for this purpose:
> +
> + (*) int security_mount_ctx_alloc(struct mount_context *mc,
> + struct super_block *src_sb);
> +
> + Called to initialise mc->security (which is preset to NULL) and allocate
> + any resources needed. It should return 0 on success and a negative error
> + code on failure.
> +
> + src_sb is non-NULL in the case of a remount (MS_REMOUNT) in which case it
> + indicates the superblock to be remounted or in the case of a submount
> + (MS_SUBMOUNT) in which case it indicates the parent superblock.
> +
> + (*) int security_mount_ctx_dup(struct mount_context *mc,
> + struct mount_context *src_mc);
> +
> + Called to initialise mc->security (which is preset to NULL) and allocate
> + any resources needed. The original mount context is pointed to by src_mc
> + and may be used for reference. It should return 0 on success and a
> + negative error code on failure.
> +
> + (*) void security_mount_ctx_free(struct mount_context *mc);
> +
> + Called to clean up anything attached to mc->security. Note that the
> + contents may have been transferred to a superblock and the pointer NULL'd
> + out during mount.
> +
> + (*) int security_mount_ctx_option(struct mount_context *mc, char *opt);
> +
> + Called for each mount option. The mount options are in "key[=val]"
> + form. An active LSM may reject one with an error, pass one over and
> + return 0 or consume one and return 1. If consumed, the option isn't
> + passed on to the filesystem.
> +
> + If it returns an error, it should set mc->error if the error is
> + ambiguous.
> +
> + (*) int security_mount_ctx_kern_mount(struct mount_context *mc,
> + struct super_block *sb);
> +
> + Called during mount to verify that the specified superblock is allowed to
> + be mounted and to transfer the security data there.
> +
> + On success, it should return 0; otherwise it should return an error and
> + set mc->error to indicate the problem. It should not return -ENOMEM as
> + this should be taken care of in advance.
> +
> + [NOTE] Should I add a security_mount_ctx_validate() operation so that the
> + LSM has the opportunity to allocate stuff and check the options as a
> + whole?
> +
> +
> +============================
> +VFS MOUNT CONTEXT OPERATIONS
> +============================
> +
> +There are four operations for creating a mount context and one for destroying
> +a context:
> +
> + (*) struct mount_context *__vfs_fsopen(struct file_system_type *fs_type,
> + struct super_block *src_sb;
> + unsigned int ms_flags,
> + unsigned int mnt_flags);
> +
> + Create a mount context given a filesystem type pointer. This allocates
> + the mount context, sets the flags, initialises the security and calls
> + fs_type->fsopen() to initialise the filesystem context.
> +
> + src_sb can be NULL or it may indicate a superblock that is going to be
> + remounted (MS_REMOUNT) or a superblock that is the parent of a submount
> + (MS_SUBMOUNT). This superblock is provided as a source of namespace
> + information.
> +
> + (*) struct mount_context *vfs_mntopen(struct vfsmount *mnt,
> + unsigned int ms_flags,
> + unsigned int mnt_flags);
> +
> + Create a mount context from the same filesystem as an extant mount and
> + initialise the mount parameters from the superblock underlying that
> + mount. This is used by remount.
> +
> + (*) struct mount_context *vfs_fsopen(const char *fs_name);
> +
> + Create a mount context given a filesystem name. It is assumed that the
> + mount flags will be passed in as text options later. This is intended to
> + be called from sys_fsopen(). This copies current's namespaces to the
> + mount context.
> +
> + (*) struct mount_context *vfs_dup_mount_context(struct mount_context *src);
> +
> + Duplicate a mount context, copying any options noted and duplicating or
> + additionally referencing any resources held therein. This is available
> + for use where a filesystem has to get a mount within a mount, such as
> + NFS4 does by internally mounting the root of the target server and then
> + doing a private pathwalk to the target directory.
> +
> + (*) void put_mount_context(struct mount_context *ctx);
> +
> + Destroy a mount context, releasing any resources it holds. This calls
> + the ->free() operation. This is intended to be called by anyone who
> + created a mount context.
> +
> + [!] Mount contexts are not refcounted, so this causes unconditional
> + destruction.
> +
> +In all the above operations, apart from the put op, the return is a mount
> +context pointer or a negative error code. No error string is saved as the
> +error string is only guaranteed as long as the file_system_type is pinned (and
> +thus the module).
> +
> +In the remaining operations, if an error occurs, a negative error code is
> +returned and, if not obvious, mc->error should be set to point to a useful
> +string. The string should not be freed.
> +
> + (*) struct vfsmount *vfs_kern_mount_mc(struct mount_context *mc);
> +
> + Create a mount given the parameters in the specified mount context. This
> + invokes the ->validate() op and then the ->mount() op.
> +
> + (*) struct vfsmount *vfs_submount_mc(const struct dentry *mountpoint,
> + struct mount_context *mc);
> +
> + Create a mount given a mount context and set MS_SUBMOUNT on it. A
> + wrapper around vfs_kern_mount_mc(). This is intended to be called from
> + filesystems that have automount points (NFS, AFS, ...).
> +
> + (*) int vfs_mount_option(struct mount_context *mc, char *data);
> +
> + Supply a single mount option to the mount context. The mount option
> + should likely be in a "key[=val]" string form. The option is first
> + checked to see if it corresponds to a standard mount flag (in which case
> + it is used to mark an MS_xxx flag and consumed) or a security option (in
> + which case the LSM consumes it) before it is passed on to the filesystem.
> +
> + (*) int generic_monolithic_mount_data(struct mount_context *ctx, void *data);
> +
> + Parse a sys_mount() data page, assuming the form to be a text list
> + consisting of key[=val] options separated by commas. Each item in the
> + list is passed to vfs_mount_option(). This is the default when the
> + ->monolithic_mount_data() operation is NULL.
> diff --git a/fs/Makefile b/fs/Makefile
> index 7bbaca9c67b1..308a104a9a07 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -11,7 +11,8 @@ obj-y := open.o read_write.o file_table.o super.o \
> attr.o bad_inode.o file.o filesystems.o namespace.o \
> seq_file.o xattr.o libfs.o fs-writeback.o \
> pnode.o splice.o sync.o utimes.o \
> - stack.o fs_struct.o statfs.o fs_pin.o nsfs.o
> + stack.o fs_struct.o statfs.o fs_pin.o nsfs.o \
> + mount_context.o
>
> ifeq ($(CONFIG_BLOCK),y)
> obj-y += buffer.o block_dev.o direct-io.o mpage.o
> diff --git a/fs/internal.h b/fs/internal.h
> index 076751d90ba2..ef8c5e93f364 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -87,7 +87,7 @@ extern struct file *get_empty_filp(void);
> /*
> * super.c
> */
> -extern int do_remount_sb(struct super_block *, int, void *, int);
> +extern int do_remount_sb(struct super_block *, int, void *, int, struct mount_context *);
> extern bool trylock_super(struct super_block *sb);
> extern struct dentry *mount_fs(struct file_system_type *,
> int, const char *, void *);
> diff --git a/fs/mount.h b/fs/mount.h
> index 2826543a131d..b1e99b38f2ee 100644
> --- a/fs/mount.h
> +++ b/fs/mount.h
> @@ -108,9 +108,10 @@ static inline void detach_mounts(struct dentry *dentry)
> __detach_mounts(dentry);
> }
>
> -static inline void get_mnt_ns(struct mnt_namespace *ns)
> +static inline struct mnt_namespace *get_mnt_ns(struct mnt_namespace *ns)
> {
> atomic_inc(&ns->count);
> + return ns;
> }
>
> extern seqlock_t mount_lock;
> diff --git a/fs/mount_context.c b/fs/mount_context.c
> new file mode 100644
> index 000000000000..7d765c100bf1
> --- /dev/null
> +++ b/fs/mount_context.c
> @@ -0,0 +1,343 @@
> +/* Provide a way to create a mount context within the kernel that can be
> + * configured before mounting.
> + *
> + * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@...hat.com)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public Licence
> + * as published by the Free Software Foundation; either version
> + * 2 of the Licence, or (at your option) any later version.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +#include <linux/fs.h>
> +#include <linux/mount.h>
> +#include <linux/nsproxy.h>
> +#include <linux/slab.h>
> +#include <linux/magic.h>
> +#include <linux/security.h>
> +#include <linux/parser.h>
> +#include <linux/mnt_namespace.h>
> +#include <linux/pid_namespace.h>
> +#include <linux/user_namespace.h>
> +#include <net/net_namespace.h>
> +#include "mount.h"
> +
> +static const match_table_t common_set_mount_options = {
> + { MS_DIRSYNC, "dirsync" },
> + { MS_I_VERSION, "iversion" },
> + { MS_LAZYTIME, "lazytime" },
> + { MS_MANDLOCK, "mand" },
> + { MS_NOATIME, "noatime" },
> + { MS_NODEV, "nodev" },
> + { MS_NODIRATIME, "nodiratime" },
> + { MS_NOEXEC, "noexec" },
> + { MS_NOSUID, "nosuid" },
> + { MS_POSIXACL, "posixacl" },
> + { MS_RDONLY, "ro" },
> + { MS_REC, "rec" },
> + { MS_RELATIME, "relatime" },
> + { MS_STRICTATIME, "strictatime" },
> + { MS_SYNCHRONOUS, "sync" },
> + { MS_VERBOSE, "verbose" },
> + { },
> +};
> +
> +static const match_table_t common_clear_mount_options = {
> + { MS_LAZYTIME, "nolazytime" },
> + { MS_MANDLOCK, "nomand" },
> + { MS_NODEV, "dev" },
> + { MS_NOEXEC, "exec" },
> + { MS_NOSUID, "suid" },
> + { MS_RDONLY, "rw" },
> + { MS_RELATIME, "norelatime" },
> + { MS_SILENT, "silent" },
> + { MS_STRICTATIME, "nostrictatime" },
> + { MS_SYNCHRONOUS, "async" },
> + { },
> +};
> +
> +static const match_table_t forbidden_mount_options = {
> + { MS_BIND, "bind" },
> + { MS_KERNMOUNT, "ro" },
> + { MS_MOVE, "move" },
> + { MS_PRIVATE, "private" },
> + { MS_REMOUNT, "remount" },
> + { MS_SHARED, "shared" },
> + { MS_SLAVE, "slave" },
> + { MS_UNBINDABLE, "unbindable" },
> + { },
> +};
> +
> +/*
> + * Check for a common mount option.
> + */
> +static noinline int vfs_common_mount_option(struct mount_context *mc, char *data)
> +{
> + substring_t args[MAX_OPT_ARGS];
> + unsigned int token;
> +
> + token = match_token(data, common_set_mount_options, args);
> + if (token) {
> + mc->ms_flags |= token;
> + return 1;
> + }
> +
> + token = match_token(data, common_clear_mount_options, args);
> + if (token) {
> + mc->ms_flags &= ~token;
> + return 1;
> + }
> +
> + token = match_token(data, forbidden_mount_options, args);
> + if (token) {
> + mc->error = "Mount option, not superblock option";
> + return -EINVAL;
> + }
> +
> + return 0;
> +}
> +
> +/**
> + * vfs_mount_option - Add a single mount option to a mount context
> + * @mc: The mount context to modify
> + * @option: The option to apply.
> + *
> + * A single mount option in string form is applied to the mount being set up in
> + * the mount context. Certain standard options (for example "ro") are
> + * translated into flag bits without going to the filesystem. The active
> + * security module allowed to observe and poach options. Any other options are
"module is allowed"
> + * passed over to the filesystem to parse.
> + *
> + * This may be called multiple times for a context.
> + *
> + * Returns 0 on success and a negative error code on failure. In the event of
> + * failure, mc->error may have been set to a non-allocated string that gives
> + * more information.
> + */
> +int vfs_mount_option(struct mount_context *mc, char *data)
> +{
> + int ret;
> +
> + if (mc->mounted)
> + return -EBUSY;
> +
> + ret = vfs_common_mount_option(mc, data);
> + if (ret < 0)
> + return ret;
> + if (ret == 1)
> + return 0;
> +
> + ret = security_mount_ctx_option(mc, data);
> + if (ret < 0)
> + return ret;
> + if (ret == 1)
> + return 0;
> +
> + return mc->ops->option(mc, data);
> +}
> +EXPORT_SYMBOL(vfs_mount_option);
> +
> +/**
> + * generic_monolithic_mount_data - Parse key[=val][,key[=val]]* mount data
> + * @mc: The mount context to populate
> + * @data: The data to parse
> + *
> + * Parse a blob of data that's in key[=val][,key[=val]]* form. This can be
> + * called from the ->monolithic_mount_data() mount context operation.
> + *
> + * Returns 0 on success or the error returned by the ->option() mount context
> + * operation on failure.
> + */
> +int generic_monolithic_mount_data(struct mount_context *ctx, void *data)
> +{
> + char *options = data, *p;
> + int ret;
> +
> + if (!options)
> + return 0;
> +
> + while ((p = strsep(&options, ",")) != NULL) {
> + if (*p) {
> + ret = vfs_mount_option(ctx, p);
> + if (ret < 0)
> + return ret;
> + }
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(generic_monolithic_mount_data);
> +
> +/**
> + * __vfs_fsopen - Open a filesystem and create a mount context
> + * @fs_type: The filesystem type
> + * @src_sb: A superblock from which this one derives (or NULL)
> + * @ms_flags: Superblock flags and op flags (such as MS_REMOUNT)
> + * @mnt_flags: Mountpoint flags, such as MNT_READONLY
> + * @mount_type: Type of mount
> + *
> + * Open a filesystem and create a mount context. The mount context is
> + * initialised with the supplied flags and, if a submount/automount from
> + * another superblock (@src_sb), may have parameters such as namespaces copied
> + * across from that superblock.
> + */
> +struct mount_context *__vfs_fsopen(struct file_system_type *fs_type,
> + struct super_block *src_sb,
> + unsigned int ms_flags, unsigned int mnt_flags,
> + enum mount_type mount_type)
> +{
> + struct mount_context *mc;
> + int ret;
> +
> + if (fs_type->fsopen && fs_type->mc_size < sizeof(*mc))
> + BUG();
> +
> + mc = kzalloc(max_t(size_t, fs_type->mc_size, sizeof(*mc)), GFP_KERNEL);
> + if (!mc)
> + return ERR_PTR(-ENOMEM);
> +
> + mc->mount_type = mount_type;
> + mc->ms_flags = ms_flags;
> + mc->mnt_flags = mnt_flags;
> + mc->fs_type = fs_type;
> + get_filesystem(fs_type);
> + mc->mnt_ns = get_mnt_ns(current->nsproxy->mnt_ns);
> + mc->pid_ns = get_pid_ns(task_active_pid_ns(current));
> + mc->net_ns = get_net(current->nsproxy->net_ns);
> + mc->user_ns = get_user_ns(current_user_ns());
> + mc->cred = get_current_cred();
> +
> +
> + /* TODO: Make all filesystems support this unconditionally */
> + if (mc->fs_type->fsopen) {
> + ret = mc->fs_type->fsopen(mc, src_sb);
> + if (ret < 0)
> + goto err_mc;
> + }
> +
> + /* Do the security check last because ->fsopen may change the
> + * namespace subscriptions.
> + */
> + ret = security_mount_ctx_alloc(mc, src_sb);
> + if (ret < 0)
> + goto err_mc;
> +
> + return mc;
> +
> +err_mc:
> + put_mount_context(mc);
> + return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(__vfs_fsopen);
> +
> +/**
> + * vfs_fsopen - Open a filesystem and create a mount context
> + * @fs_name: The name of the filesystem
> + *
> + * Open a filesystem and create a mount context that will hold the mount
> + * options, device name, security details, etc.. Note that the caller should
> + * check the ->ops pointer in the returned context to determine whether the
> + * filesystem actually supports the mount context itself.
> + */
> +struct mount_context *vfs_fsopen(const char *fs_name)
> +{
> + struct file_system_type *fs_type;
> + struct mount_context *mc;
> +
> + fs_type = get_fs_type(fs_name);
> + if (!fs_type)
> + return ERR_PTR(-ENODEV);
> +
> + mc = __vfs_fsopen(fs_type, NULL, 0, 0, MOUNT_TYPE_NEW);
> + put_filesystem(fs_type);
> + return mc;
> +}
> +EXPORT_SYMBOL(vfs_fsopen);
> +
> +/**
> + * vfs_mntopen - Create a mount context and initialise it from an extant mount
> + * @mnt: The mountpoint to open
> + * @ms_flags: Superblock flags and op flags (such as MS_REMOUNT)
> + * @mnt_flags: Mountpoint flags, such as MNT_READONLY
> + * @mount_type: Type of mount
> + *
> + * Open a mounted filesystem and create a mount context such that a remount can
> + * be effected.
> + */
> +struct mount_context *vfs_mntopen(struct vfsmount *mnt,
> + unsigned int ms_flags,
> + unsigned int mnt_flags,
> + enum mount_type mount_type)
> +{
> + return __vfs_fsopen(mnt->mnt_sb->s_type, mnt->mnt_sb,
> + ms_flags, mnt_flags, mount_type);
> +}
> +
> +/**
> + * vfs_dup_mount_context: Duplicate a mount context.
> + * @src: The mount context to copy.
> + */
> +struct mount_context *vfs_dup_mount_context(struct mount_context *src)
> +{
> + struct mount_context *mc;
> + int ret;
> +
> + if (!src->ops->dup)
> + return ERR_PTR(-ENOTSUPP);
> +
> + mc = kmemdup(src, src->fs_type->mc_size, GFP_KERNEL);
> + if (!mc)
> + return ERR_PTR(-ENOMEM);
> +
> + mc->device = NULL;
> + mc->root_path = NULL;
> + mc->security = NULL;
> + mc->error = NULL;
> + get_filesystem(mc->fs_type);
> + get_mnt_ns(mc->mnt_ns);
> + get_pid_ns(mc->pid_ns);
> + get_net(mc->net_ns);
> + get_user_ns(mc->user_ns);
> + get_cred(mc->cred);
> +
> + /* Can't call put until we've called ->dup */
> + ret = mc->ops->dup(mc, src);
> + if (ret < 0)
> + goto err_mc;
> +
> + ret = security_mount_ctx_dup(mc, src);
> + if (ret < 0)
> + goto err_mc;
> + return mc;
> +
> +err_mc:
> + put_mount_context(mc);
> + return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(vfs_dup_mount_context);
> +
> +/*
> + * Dispose of a mount context.
> + */
> +void put_mount_context(struct mount_context *mc)
> +{
> + if (mc->ops && mc->ops->free)
> + mc->ops->free(mc);
> + security_mount_ctx_free(mc);
> + if (mc->mnt_ns)
> + put_mnt_ns(mc->mnt_ns);
> + if (mc->pid_ns)
> + put_pid_ns(mc->pid_ns);
> + if (mc->net_ns)
> + put_net(mc->net_ns);
> + put_user_ns(mc->user_ns);
> + if (mc->cred)
> + put_cred(mc->cred);
> + put_filesystem(mc->fs_type);
> + kfree(mc->device);
> + kfree(mc->root_path);
> + kfree(mc);
> +}
> +EXPORT_SYMBOL(put_mount_context);
> diff --git a/fs/namespace.c b/fs/namespace.c
> index db034b6afd43..e0edab9af308 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -25,6 +25,7 @@
> #include <linux/magic.h>
> #include <linux/bootmem.h>
> #include <linux/task_work.h>
> +#include <linux/file.h>
> #include <linux/sched/task.h>
>
> #include "pnode.h"
> @@ -783,9 +784,14 @@ static void put_mountpoint(struct mountpoint *mp)
> }
> }
>
> +static inline int __check_mnt(struct mount *mnt, struct mnt_namespace *mnt_ns)
> +{
> + return mnt->mnt_ns == mnt_ns;
> +}
> +
> static inline int check_mnt(struct mount *mnt)
> {
> - return mnt->mnt_ns == current->nsproxy->mnt_ns;
> + return __check_mnt(mnt, current->nsproxy->mnt_ns);
> }
>
> /*
> @@ -1596,7 +1602,7 @@ static int do_umount(struct mount *mnt, int flags)
> return -EPERM;
> down_write(&sb->s_umount);
> if (!(sb->s_flags & MS_RDONLY))
> - retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
> + retval = do_remount_sb(sb, MS_RDONLY, NULL, 0, NULL);
> up_write(&sb->s_umount);
> return retval;
> }
> @@ -2279,6 +2285,26 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
> }
>
> /*
> + * Parse the monolithic page of mount data given to sys_mount().
> + */
> +static int parse_monolithic_mount_data(struct mount_context *mc, void *data)
> +{
> + int (*monolithic_mount_data)(struct mount_context *, void *);
> + int ret;
> +
> + monolithic_mount_data = mc->ops->monolithic_mount_data;
> + if (!monolithic_mount_data)
> + monolithic_mount_data = generic_monolithic_mount_data;
> +
> + ret = monolithic_mount_data(mc, data);
> + if (ret < 0)
> + return ret;
> + if (mc->ops->validate)
> + return mc->ops->validate(mc);
> + return 0;
> +}
> +
> +/*
> * change filesystem flags. dir should be a physical root of filesystem.
> * If you've mounted a non-root directory somewhere and want to do remount
> * on it - tough luck.
> @@ -2286,13 +2312,14 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
> static int do_remount(struct path *path, int flags, int mnt_flags,
> void *data)
> {
> + struct mount_context *mc = NULL;
> int err;
> struct super_block *sb = path->mnt->mnt_sb;
> struct mount *mnt = real_mount(path->mnt);
> + struct file_system_type *type = sb->s_type;
>
> if (!check_mnt(mnt))
> return -EINVAL;
> -
> if (path->dentry != path->mnt->mnt_root)
> return -EINVAL;
>
> @@ -2323,9 +2350,19 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
> return -EPERM;
> }
>
> - err = security_sb_remount(sb, data);
> - if (err)
> - return err;
> + if (type->fsopen) {
> + mc = vfs_mntopen(path->mnt, flags, mnt_flags, MOUNT_TYPE_REMOUNT);
> + if (IS_ERR(mc))
> + return PTR_ERR(mc);
> +
> + err = parse_monolithic_mount_data(mc, data);
> + if (err < 0)
> + goto err_mc;
> + } else {
> + err = security_sb_remount(sb, data);
> + if (err)
> + return err;
> + }
>
> down_write(&sb->s_umount);
> if (flags & MS_BIND)
> @@ -2333,7 +2370,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
> else if (!capable(CAP_SYS_ADMIN))
> err = -EPERM;
> else
> - err = do_remount_sb(sb, flags, data, 0);
> + err = do_remount_sb(sb, flags, data, 0, mc);
> if (!err) {
> lock_mount_hash();
> mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
> @@ -2342,6 +2379,9 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
> unlock_mount_hash();
> }
> up_write(&sb->s_umount);
> +err_mc:
> + if (mc)
> + put_mount_context(mc);
> return err;
> }
>
> @@ -2451,7 +2491,8 @@ static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
> /*
> * add a mount into a namespace's mount tree
> */
> -static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
> +static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags,
> + struct mnt_namespace *mnt_ns)
> {
> struct mountpoint *mp;
> struct mount *parent;
> @@ -2465,7 +2506,7 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
>
> parent = real_mount(path->mnt);
> err = -EINVAL;
> - if (unlikely(!check_mnt(parent))) {
> + if (unlikely(!__check_mnt(parent, mnt_ns))) {
> /* that's acceptable only for automounts done in private ns */
> if (!(mnt_flags & MNT_SHRINKABLE))
> goto unlock;
> @@ -2493,42 +2534,73 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
> }
>
> static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
> +static int do_new_mount_mc(struct mount_context *mc, struct path *mountpoint,
> + unsigned int mnt_flags);
>
> /*
> * create a new mount for userspace and request it to be added into the
> * namespace's tree
> */
> -static int do_new_mount(struct path *path, const char *fstype, int flags,
> +static int do_new_mount(struct path *mountpoint, const char *fstype, int flags,
> int mnt_flags, const char *name, void *data)
> {
> - struct file_system_type *type;
> + struct mount_context *mc;
> struct vfsmount *mnt;
> int err;
>
> if (!fstype)
> return -EINVAL;
>
> - type = get_fs_type(fstype);
> - if (!type)
> - return -ENODEV;
> + mc = vfs_fsopen(fstype);
> + if (IS_ERR(mc))
> + return PTR_ERR(mc);
> + mc->ms_flags = flags;
> + mc->mnt_flags = mnt_flags;
>
> - mnt = vfs_kern_mount(type, flags, name, data);
> - if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
> - !mnt->mnt_sb->s_subtype)
> - mnt = fs_set_subtype(mnt, fstype);
> + err = -ENOMEM;
> + mc->device = kstrdup(name, GFP_KERNEL);
> + if (!mc->device)
> + goto err_mc;
>
> - put_filesystem(type);
> - if (IS_ERR(mnt))
> - return PTR_ERR(mnt);
> + if (mc->ops) {
> + err = parse_monolithic_mount_data(mc, data);
> + if (err < 0)
> + goto err_mc;
>
> - if (mount_too_revealing(mnt, &mnt_flags)) {
> - mntput(mnt);
> - return -EPERM;
> + err = do_new_mount_mc(mc, mountpoint, mnt_flags);
> + if (err)
> + goto err_mc;
> +
> + } else {
> + mnt = vfs_kern_mount(mc->fs_type, flags, name, data);
> + if (!IS_ERR(mnt) && (mc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
> + !mnt->mnt_sb->s_subtype)
> + mnt = fs_set_subtype(mnt, fstype);
> +
> + if (IS_ERR(mnt)) {
> + err = PTR_ERR(mnt);
> + goto err_mc;
> + }
> +
> + err = -EPERM;
> + if (mount_too_revealing(mnt, &mnt_flags))
> + goto err_mnt;
> +
> + err = do_add_mount(real_mount(mnt), mountpoint, mnt_flags,
> + mc->mnt_ns);
> + if (err)
> + goto err_mnt;
> }
>
> - err = do_add_mount(real_mount(mnt), path, mnt_flags);
> - if (err)
> - mntput(mnt);
> + put_mount_context(mc);
> + return 0;
> +
> +err_mnt:
> + mntput(mnt);
> +err_mc:
> + if (mc->error)
> + pr_info("Mount failed: %s\n", mc->error);
> + put_mount_context(mc);
> return err;
> }
>
> @@ -2547,7 +2619,8 @@ int finish_automount(struct vfsmount *m, struct path *path)
> goto fail;
> }
>
> - err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
> + err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE,
> + current->nsproxy->mnt_ns);
> if (!err)
> return 0;
> fail:
> @@ -3061,6 +3134,130 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
> return ret;
> }
>
> +static struct dentry *__do_mount_mc(struct mount_context *mc)
> +{
> + struct super_block *sb;
> + struct dentry *root;
> + int ret;
> +
> + root = mc->ops->mount(mc);
> + if (IS_ERR(root))
> + return root;
> +
> + sb = root->d_sb;
> + BUG_ON(!sb);
> + WARN_ON(!sb->s_bdi);
> + sb->s_flags |= MS_BORN;
> +
> + ret = security_mount_ctx_kern_mount(mc, sb);
> + if (ret < 0)
> + goto err_sb;
> +
> + /*
> + * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
> + * but s_maxbytes was an unsigned long long for many releases. Throw
> + * this warning for a little while to try and catch filesystems that
> + * violate this rule.
> + */
> + WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
> + "negative value (%lld)\n", mc->fs_type->name, sb->s_maxbytes);
> +
> + up_write(&sb->s_umount);
> + return root;
> +
> +err_sb:
> + dput(root);
> + deactivate_locked_super(sb);
> + return ERR_PTR(ret);
> +}
> +
> +struct vfsmount *vfs_kern_mount_mc(struct mount_context *mc)
> +{
> + struct dentry *root;
> + struct mount *mnt;
> + int ret;
> +
> + if (mc->ops->validate) {
> + ret = mc->ops->validate(mc);
> + if (ret < 0)
> + return ERR_PTR(ret);
> + }
> +
> + mnt = alloc_vfsmnt(mc->device ?: "none");
> + if (!mnt)
> + return ERR_PTR(-ENOMEM);
> +
> + if (mc->ms_flags & MS_KERNMOUNT)
> + mnt->mnt.mnt_flags = MNT_INTERNAL;
> +
> + root = __do_mount_mc(mc);
> + if (IS_ERR(root)) {
> + mnt_free_id(mnt);
> + free_vfsmnt(mnt);
> + return ERR_CAST(root);
> + }
> +
> + mnt->mnt.mnt_root = root;
> + mnt->mnt.mnt_sb = root->d_sb;
> + mnt->mnt_mountpoint = mnt->mnt.mnt_root;
> + mnt->mnt_parent = mnt;
> + lock_mount_hash();
> + list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
> + unlock_mount_hash();
> + return &mnt->mnt;
> +}
> +EXPORT_SYMBOL_GPL(vfs_kern_mount_mc);
> +
> +struct vfsmount *
> +vfs_submount_mc(const struct dentry *mountpoint, struct mount_context *mc)
> +{
> + /* Until it is worked out how to pass the user namespace
> + * through from the parent mount to the submount don't support
> + * unprivileged mounts with submounts.
> + */
> + if (mountpoint->d_sb->s_user_ns != &init_user_ns)
> + return ERR_PTR(-EPERM);
> +
> + mc->ms_flags = MS_SUBMOUNT;
> + return vfs_kern_mount_mc(mc);
> +}
> +EXPORT_SYMBOL_GPL(vfs_submount_mc);
> +
> +static int do_new_mount_mc(struct mount_context *mc, struct path *mountpoint,
> + unsigned int mnt_flags)
> +{
> + struct vfsmount *mnt;
> + int ret;
> +
> + mnt = vfs_kern_mount_mc(mc);
> + if (IS_ERR(mnt))
> + return PTR_ERR(mnt);
> +
> + if ((mc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
> + !mnt->mnt_sb->s_subtype) {
> + mnt = fs_set_subtype(mnt, mc->fs_type->name);
> + if (IS_ERR(mnt))
> + return PTR_ERR(mnt);
> + }
> +
> + ret = -EPERM;
> + if (mount_too_revealing(mnt, &mnt_flags)) {
> + mc->error = "VFS: Mount too revealing";
> + goto err_mnt;
> + }
> +
> + ret = do_add_mount(real_mount(mnt), mountpoint, mnt_flags, mc->mnt_ns);
> + if (ret < 0) {
> + mc->error = "VFS: Failed to add mount";
> + goto err_mnt;
> + }
> + return ret;
> +
> +err_mnt:
> + mntput(mnt);
> + return ret;
> +}
> +
> /*
> * Return true if path is reachable from root
> *
> @@ -3302,6 +3499,23 @@ struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
> }
> EXPORT_SYMBOL_GPL(kern_mount_data);
>
> +struct vfsmount *kern_mount_data_mc(struct mount_context *mc)
> +{
> + struct vfsmount *mnt;
> +
> + mc->ms_flags = MS_KERNMOUNT;
> + mnt = vfs_kern_mount_mc(mc);
> + if (!IS_ERR(mnt)) {
> + /*
> + * it is a longterm mount, don't release mnt until
> + * we unmount before file sys is unregistered
> + */
> + real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
> + }
> + return mnt;
> +}
> +EXPORT_SYMBOL_GPL(kern_mount_data_mc);
> +
> void kern_unmount(struct vfsmount *mnt)
> {
> /* release long term mount so mount point can be released */
> diff --git a/fs/super.c b/fs/super.c
> index adb0c0de428c..6e7b86520337 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -805,10 +805,13 @@ struct super_block *user_get_super(dev_t dev)
> * @flags: numeric part of options
> * @data: the rest of options
> * @force: whether or not to force the change
> + * @mc: the mount context for filesystems that support it
> + * (NULL if called from emergency or umount)
> *
> * Alters the mount options of a mounted file system.
> */
> -int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
> +int do_remount_sb(struct super_block *sb, int flags, void *data, int force,
> + struct mount_context *mc)
> {
> int retval;
> int remount_ro;
> @@ -850,8 +853,14 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
> }
> }
>
> - if (sb->s_op->remount_fs) {
> - retval = sb->s_op->remount_fs(sb, &flags, data);
> + if (sb->s_op->remount_fs_mc ||
> + sb->s_op->remount_fs) {
> + if (sb->s_op->remount_fs_mc) {
> + retval = sb->s_op->remount_fs_mc(sb, mc);
> + flags = mc->ms_flags;
> + } else {
> + retval = sb->s_op->remount_fs(sb, &flags, data);
> + }
> if (retval) {
> if (!force)
> goto cancel_readonly;
> @@ -898,7 +907,7 @@ static void do_emergency_remount(struct work_struct *work)
> /*
> * What lock protects sb->s_flags??
> */
> - do_remount_sb(sb, MS_RDONLY, NULL, 1);
> + do_remount_sb(sb, MS_RDONLY, NULL, 1, NULL);
> }
> up_write(&sb->s_umount);
> spin_lock(&sb_lock);
> @@ -1048,6 +1057,37 @@ struct dentry *mount_ns(struct file_system_type *fs_type,
>
> EXPORT_SYMBOL(mount_ns);
>
> +struct dentry *mount_ns_mc(struct mount_context *mc, void *ns)
> +{
> + struct super_block *sb;
> +
> + /* Don't allow mounting unless the caller has CAP_SYS_ADMIN
> + * over the namespace.
> + */
> + if (!(mc->ms_flags & MS_KERNMOUNT) &&
> + !ns_capable(mc->user_ns, CAP_SYS_ADMIN))
> + return ERR_PTR(-EPERM);
> +
> + sb = sget_userns(mc->fs_type, ns_test_super, ns_set_super,
> + mc->ms_flags, mc->user_ns, ns);
> + if (IS_ERR(sb))
> + return ERR_CAST(sb);
> +
> + if (!sb->s_root) {
> + int err;
> + err = mc->ops->fill_super(sb, mc);
> + if (err) {
> + deactivate_locked_super(sb);
> + return ERR_PTR(err);
> + }
> +
> + sb->s_flags |= MS_ACTIVE;
> + }
> +
> + return dget(sb->s_root);
> +}
> +EXPORT_SYMBOL(mount_ns_mc);
> +
> #ifdef CONFIG_BLOCK
> static int set_bdev_super(struct super_block *s, void *data)
> {
> @@ -1196,7 +1236,7 @@ struct dentry *mount_single(struct file_system_type *fs_type,
> }
> s->s_flags |= MS_ACTIVE;
> } else {
> - do_remount_sb(s, flags, data, 0);
> + do_remount_sb(s, flags, data, 0, NULL);
> }
> return dget(s->s_root);
> }
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 30e5c14bd743..40fe5c5054ec 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -55,6 +55,7 @@ struct workqueue_struct;
> struct iov_iter;
> struct fscrypt_info;
> struct fscrypt_operations;
> +struct mount_context;
>
> extern void __init inode_init(void);
> extern void __init inode_init_early(void);
> @@ -701,6 +702,11 @@ static inline void inode_unlock(struct inode *inode)
> up_write(&inode->i_rwsem);
> }
>
> +static inline int inode_lock_killable(struct inode *inode)
> +{
> + return down_write_killable(&inode->i_rwsem);
> +}
> +
> static inline void inode_lock_shared(struct inode *inode)
> {
> down_read(&inode->i_rwsem);
> @@ -1786,6 +1792,7 @@ struct super_operations {
> int (*unfreeze_fs) (struct super_block *);
> int (*statfs) (struct dentry *, struct kstatfs *);
> int (*remount_fs) (struct super_block *, int *, char *);
> + int (*remount_fs_mc) (struct super_block *, struct mount_context *);
> void (*umount_begin) (struct super_block *);
>
> int (*show_options)(struct seq_file *, struct dentry *);
> @@ -2020,8 +2027,10 @@ struct file_system_type {
> #define FS_HAS_SUBTYPE 4
> #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
> #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
> + unsigned short mc_size; /* Size of mount context to allocate */
> struct dentry *(*mount) (struct file_system_type *, int,
> const char *, void *);
> + int (*fsopen)(struct mount_context *, struct super_block *);
> void (*kill_sb) (struct super_block *);
> struct module *owner;
> struct file_system_type * next;
> @@ -2039,6 +2048,7 @@ struct file_system_type {
>
> #define MODULE_ALIAS_FS(NAME) MODULE_ALIAS("fs-" NAME)
>
> +extern struct dentry *mount_ns_mc(struct mount_context *mc, void *ns);
> extern struct dentry *mount_ns(struct file_system_type *fs_type,
> int flags, void *data, void *ns, struct user_namespace *user_ns,
> int (*fill_super)(struct super_block *, void *, int));
> @@ -2105,6 +2115,7 @@ extern int register_filesystem(struct file_system_type *);
> extern int unregister_filesystem(struct file_system_type *);
> extern struct vfsmount *kern_mount_data(struct file_system_type *, void *data);
> #define kern_mount(type) kern_mount_data(type, NULL)
> +extern struct vfsmount *kern_mount_data_mc(struct mount_context *);
> extern void kern_unmount(struct vfsmount *mnt);
> extern int may_umount_tree(struct vfsmount *);
> extern int may_umount(struct vfsmount *);
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index e29d4c62a3c8..f6aa68b8e68e 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -75,6 +75,32 @@
> * should enable secure mode.
> * @bprm contains the linux_binprm structure.
> *
> + * Security hooks for mount using fd context.
> + *
> + * @mount_ctx_alloc:
> + * Allocate and attach a security structure to mc->security. This pointer
> + * is initialised to NULL by the caller.
> + * @mc indicates the new mount context.
> + * @src_sb indicates the source superblock of a submount.
> + * @mount_ctx_dup:
> + * Allocate and attach a security structure to mc->security. This pointer
> + * is initialised to NULL by the caller.
> + * @mc indicates the new mount context.
> + * @src_mc indicates the original mount context.
> + * @mount_ctx_free:
> + * Clean up a mount context.
> + * @mc indicates the mount context.
> + * @mount_ctx_option:
> + * Userspace provided an option to configure a mount. The LSM may reject
> + * it with an error and may use it for itself, in which case it should
> + * return 1; otherwise it should return 0 to pass it on to the filesystem.
> + * @mc indicates the mount context.
> + * @p indicates the option in "key[=val]" form.
> + * @mount_ctx_kern_mount:
> + * Equivalent of sb_kern_mount, but with a mount_context.
> + * @mc indicates the mount context.
> + * @src_sb indicates the new superblock.
> + *
> * Security hooks for filesystem operations.
> *
> * @sb_alloc_security:
> @@ -1358,6 +1384,12 @@ union security_list_options {
> void (*bprm_committing_creds)(struct linux_binprm *bprm);
> void (*bprm_committed_creds)(struct linux_binprm *bprm);
>
> + int (*mount_ctx_alloc)(struct mount_context *mc, struct super_block *src_sb);
> + int (*mount_ctx_dup)(struct mount_context *mc, struct mount_context *src_mc);
> + void (*mount_ctx_free)(struct mount_context *mc);
> + int (*mount_ctx_option)(struct mount_context *mc, char *opt);
> + int (*mount_ctx_kern_mount)(struct mount_context *mc, struct super_block *sb);
> +
> int (*sb_alloc_security)(struct super_block *sb);
> void (*sb_free_security)(struct super_block *sb);
> int (*sb_copy_data)(char *orig, char *copy);
> @@ -1666,6 +1698,11 @@ struct security_hook_heads {
> struct list_head bprm_secureexec;
> struct list_head bprm_committing_creds;
> struct list_head bprm_committed_creds;
> + struct list_head mount_ctx_alloc;
> + struct list_head mount_ctx_dup;
> + struct list_head mount_ctx_free;
> + struct list_head mount_ctx_option;
> + struct list_head mount_ctx_kern_mount;
> struct list_head sb_alloc_security;
> struct list_head sb_free_security;
> struct list_head sb_copy_data;
> diff --git a/include/linux/mount.h b/include/linux/mount.h
> index 8e0352af06b7..cf2583406986 100644
> --- a/include/linux/mount.h
> +++ b/include/linux/mount.h
> @@ -69,6 +69,56 @@ struct vfsmount {
> int mnt_flags;
> };
>
> +struct mount_context;
> +struct mount_context_operations {
> + void (*free)(struct mount_context *mc);
> + int (*dup)(struct mount_context *mc, struct mount_context *src);
> + /* An option has been specified. */
> + int (*option)(struct mount_context *mc, char *p);
> + /* Parse monolithic mount data. */
> + int (*monolithic_mount_data)(struct mount_context *mc, void *data);
> + /* Validate the mount options */
> + int (*validate)(struct mount_context *mc);
> + /* Perform the mount. */
> + struct dentry *(*mount)(struct mount_context *mc);
> + /* Fill in a superblock */
> + int (*fill_super)(struct super_block *s, struct mount_context *mc);
> +};
> +
> +enum mount_type {
> + MOUNT_TYPE_NEW, /* New mount made directly */
> + MOUNT_TYPE_SUBMOUNT, /* New mount made automatically */
> + MOUNT_TYPE_REMOUNT, /* Change of an existing mount */
> +};
> +
> +/*
> + * Mount context as allocated and constructed by fsopen(). The filesystem must
> + * support the ->ctx_*() operations. The size of the object allocated is in
> + * struct file_system_type::mount_context_size; this must be embedded as the
> + * fist thing in the filesystem's own context.
> + */
> +struct mount_context {
> + const struct mount_context_operations *ops;
> + struct file_system_type *fs_type;
> + struct user_namespace *user_ns; /* The user namespace for this mount */
> + struct mnt_namespace *mnt_ns; /* The mount namespace for this mount */
> + struct pid_namespace *pid_ns; /* The process ID namespace for this mount */
> + struct net *net_ns; /* The network namespace for this mount */
> + const struct cred *cred; /* The mounter's credentials */
> + char *device; /* The device name or mount target */
> + char *root_path; /* The path within the mount to mount */
> + void *security; /* The LSM context */
> + const char *error; /* Error string to be read by read() */
> + unsigned int ms_flags; /* The superblock flags (MS_*) */
> + unsigned int mnt_flags; /* The mount flags (MNT_*) */
> + bool mounted; /* Set when mounted */
> + bool sloppy; /* Unrecognised options are okay */
> + bool silent;
> + enum mount_type mount_type : 8;
> +};
> +
> +extern const struct file_operations fs_fs_fops;
> +
> struct file; /* forward dec */
> struct path;
>
> @@ -90,9 +140,26 @@ struct file_system_type;
> extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
> int flags, const char *name,
> void *data);
> +extern struct vfsmount *vfs_kern_mount_mc(struct mount_context *mc);
> extern struct vfsmount *vfs_submount(const struct dentry *mountpoint,
> struct file_system_type *type,
> const char *name, void *data);
> +extern struct vfsmount *vfs_submount_mc(const struct dentry *mountpoint,
> + struct mount_context *mc);
> +extern struct mount_context *vfs_fsopen(const char *fs_name);
> +extern struct mount_context *__vfs_fsopen(struct file_system_type *fs_type,
> + struct super_block *src_sb,
> + unsigned int ms_flags,
> + unsigned int mnt_flags,
> + enum mount_type mount_type);
> +extern struct mount_context *vfs_mntopen(struct vfsmount *mnt,
> + unsigned int ms_flags,
> + unsigned int mnt_flags,
> + enum mount_type mount_type);
> +extern struct mount_context *vfs_dup_mount_context(struct mount_context *src);
> +extern int vfs_mount_option(struct mount_context *mc, char *data);
> +extern int generic_monolithic_mount_data(struct mount_context *ctx, void *data);
> +extern void put_mount_context(struct mount_context *ctx);
>
> extern void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list);
> extern void mark_mounts_for_expiry(struct list_head *mounts);
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 96899fad7016..91efe3039bff 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -55,6 +55,7 @@ struct msg_queue;
> struct xattr;
> struct xfrm_sec_ctx;
> struct mm_struct;
> +struct mount_context;
>
> /* If capable should audit the security request */
> #define SECURITY_CAP_NOAUDIT 0
> @@ -220,6 +221,11 @@ int security_bprm_check(struct linux_binprm *bprm);
> void security_bprm_committing_creds(struct linux_binprm *bprm);
> void security_bprm_committed_creds(struct linux_binprm *bprm);
> int security_bprm_secureexec(struct linux_binprm *bprm);
> +int security_mount_ctx_alloc(struct mount_context *mc, struct super_block *sb);
> +int security_mount_ctx_dup(struct mount_context *mc, struct mount_context *src);
> +void security_mount_ctx_free(struct mount_context *mc);
> +int security_mount_ctx_option(struct mount_context *mc, char *opt);
> +int security_mount_ctx_kern_mount(struct mount_context *mc, struct super_block *sb);
> int security_sb_alloc(struct super_block *sb);
> void security_sb_free(struct super_block *sb);
> int security_sb_copy_data(char *orig, char *copy);
> @@ -513,6 +519,29 @@ static inline int security_bprm_secureexec(struct linux_binprm *bprm)
> return cap_bprm_secureexec(bprm);
> }
>
> +static inline int security_mount_ctx_alloc(struct mount_context *mc,
> + struct super_block *src_sb)
> +{
> + return 0;
> +}
> +static inline int security_mount_ctx_dup(struct mount_context *mc,
> + struct mount_context *src)
> +{
> + return 0;
> +}
> +static inline void security_mount_ctx_free(struct mount_context *mc)
> +{
> +}
> +static inline int security_mount_ctx_option(struct mount_context *mc, char *opt)
> +{
> + return 0;
> +}
> +static inline int security_mount_ctx_kern_mount(struct mount_context *mc,
> + struct super_block *sb)
> +{
> + return 0;
> +}
> +
> static inline int security_sb_alloc(struct super_block *sb)
> {
> return 0;
> diff --git a/security/security.c b/security/security.c
> index 23555c5504f6..2e522361df66 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -309,6 +309,31 @@ int security_bprm_secureexec(struct linux_binprm *bprm)
> return call_int_hook(bprm_secureexec, 0, bprm);
> }
>
> +int security_mount_ctx_alloc(struct mount_context *mc, struct super_block *src_sb)
> +{
> + return call_int_hook(mount_ctx_alloc, 0, mc, src_sb);
> +}
> +
> +int security_mount_ctx_dup(struct mount_context *mc, struct mount_context *src_mc)
> +{
> + return call_int_hook(mount_ctx_dup, 0, mc, src_mc);
> +}
> +
> +void security_mount_ctx_free(struct mount_context *mc)
> +{
> + call_void_hook(mount_ctx_free, mc);
> +}
> +
> +int security_mount_ctx_option(struct mount_context *mc, char *opt)
> +{
> + return call_int_hook(mount_ctx_option, 0, mc, opt);
> +}
> +
> +int security_mount_ctx_kern_mount(struct mount_context *mc, struct super_block *sb)
> +{
> + return call_int_hook(mount_ctx_kern_mount, 0, mc, sb);
> +}
> +
> int security_sb_alloc(struct super_block *sb)
> {
> return call_int_hook(sb_alloc_security, 0, sb);
> @@ -1659,6 +1684,13 @@ struct security_hook_heads security_hook_heads = {
> LIST_HEAD_INIT(security_hook_heads.bprm_committing_creds),
> .bprm_committed_creds =
> LIST_HEAD_INIT(security_hook_heads.bprm_committed_creds),
> + .mount_ctx_alloc = LIST_HEAD_INIT(security_hook_heads.mount_ctx_alloc),
> + .mount_ctx_dup = LIST_HEAD_INIT(security_hook_heads.mount_ctx_dup),
> + .mount_ctx_free = LIST_HEAD_INIT(security_hook_heads.mount_ctx_free),
> + .mount_ctx_option =
> + LIST_HEAD_INIT(security_hook_heads.mount_ctx_option),
> + .mount_ctx_kern_mount =
> + LIST_HEAD_INIT(security_hook_heads.mount_ctx_kern_mount),
> .sb_alloc_security =
> LIST_HEAD_INIT(security_hook_heads.sb_alloc_security),
> .sb_free_security =
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 0c2ac318aa7f..cf38db840f71 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2826,6 +2826,179 @@ static int selinux_umount(struct vfsmount *mnt, int flags)
> FILESYSTEM__UNMOUNT, NULL);
> }
>
> +/* fsopen mount context operations */
> +
> +static int selinux_mount_ctx_alloc(struct mount_context *mc,
> + struct super_block *src_sb)
> +{
> + struct security_mnt_opts *opts;
> +
> + opts = kzalloc(sizeof(*opts), GFP_KERNEL);
> + if (!opts)
> + return -ENOMEM;
> +
> + mc->security = opts;
> + return 0;
> +}
> +
> +static int selinux_mount_ctx_dup(struct mount_context *mc,
> + struct mount_context *src_mc)
> +{
> + const struct security_mnt_opts *src = src_mc->security;
> + struct security_mnt_opts *opts;
> + int i, n;
> +
> + opts = kzalloc(sizeof(*opts), GFP_KERNEL);
> + if (!opts)
> + return -ENOMEM;
> + mc->security = opts;
> +
> + if (!src || !src->num_mnt_opts)
> + return 0;
> + n = opts->num_mnt_opts = src->num_mnt_opts;
> +
> + if (opts->mnt_opts) {
> + opts->mnt_opts = kcalloc(n, sizeof(char *), GFP_KERNEL);
> + if (!opts->mnt_opts)
> + return -ENOMEM;
> +
> + for (i = 0; i < n; i++) {
> + if (src->mnt_opts[i]) {
> + opts->mnt_opts[i] = kstrdup(src->mnt_opts[i],
> + GFP_KERNEL);
> + if (!opts->mnt_opts[i])
> + return -ENOMEM;
> + }
> + }
> + }
> +
> + if (src->mnt_opts_flags) {
> + opts->mnt_opts_flags = kmemdup(src->mnt_opts_flags,
> + n * sizeof(int), GFP_KERNEL);
> + if (!opts->mnt_opts_flags)
> + return -ENOMEM;
> + }
> +
> + return 0;
> +}
> +
> +static void selinux_mount_ctx_free(struct mount_context *mc)
> +{
> + struct security_mnt_opts *opts = mc->security;
> +
> + security_free_mnt_opts(opts);
> + mc->security = NULL;
> +}
> +
> +static int selinux_mount_ctx_option(struct mount_context *mc, char *opt)
> +{
> + struct security_mnt_opts *opts = mc->security;
> + substring_t args[MAX_OPT_ARGS];
> + unsigned int have;
> + char *c, **oo;
> + void *old;
> + int token, ctx, i;
> +
> + token = match_token(opt, tokens, args);
> + if (token == Opt_error)
> + return 0; /* Doesn't belong to us. */
> +
> + have = 0;
> + for (i = 0; i < opts->num_mnt_opts; i++)
> + have |= 1 << opts->mnt_opts_flags[i];
> + if (have & (1 << token)) {
> + mc->error = "SELinux: Duplicate mount options";
> + return -EINVAL;
> + }
> +
> + switch (token) {
> + case Opt_context:
> + if (have & (1 << Opt_defcontext))
> + goto incompatible;
> + ctx = CONTEXT_MNT;
> + goto copy_context_string;
> +
> + case Opt_fscontext:
> + ctx = FSCONTEXT_MNT;
> + goto copy_context_string;
> +
> + case Opt_rootcontext:
> + ctx = ROOTCONTEXT_MNT;
> + goto copy_context_string;
> +
> + case Opt_defcontext:
> + if (have & (1 << Opt_context))
> + goto incompatible;
> + ctx = DEFCONTEXT_MNT;
> + goto copy_context_string;
> +
> + case Opt_labelsupport:
> + return 1;
> +
> + default:
> + mc->error = "SELinux: Unknown mount option";
> + return -EINVAL;
> + }
> +
> +copy_context_string:
> + if (opts->num_mnt_opts > 3) {
> + mc->error = "SELinux: Too many options";
> + return -EINVAL;
> + }
> + if (!opts->mnt_opts_flags) {
> + opts->mnt_opts_flags = kcalloc(3, sizeof(int), GFP_KERNEL);
> + if (!opts->mnt_opts_flags)
> + return -ENOMEM;
> + }
> +
> + if (opts->mnt_opts) {
> + oo = kmalloc((opts->num_mnt_opts + 1) * sizeof(char *),
> + GFP_KERNEL);
> + if (!oo)
> + return -ENOMEM;
> + memcpy(oo, opts->mnt_opts, opts->num_mnt_opts * sizeof(char *));
> + oo[opts->num_mnt_opts] = NULL;
> + old = opts->mnt_opts;
> + opts->mnt_opts = oo;
> + kfree(old);
> + }
> +
> + c = match_strdup(&args[0]);
> + if (!c)
> + return -ENOMEM;
> + opts->mnt_opts[opts->num_mnt_opts] = c;
> + opts->mnt_opts_flags[opts->num_mnt_opts] = ctx;
> + opts->num_mnt_opts++;
> + return 1;
> +
> +incompatible:
> + mc->error = "SELinux: Incompatible mount options";
> + return -EINVAL;
> +}
> +
> +static int selinux_mount_ctx_kern_mount(struct mount_context *mc,
> + struct super_block *sb)
> +{
> + const struct cred *cred = current_cred();
> + struct common_audit_data ad;
> + int rc;
> +
> + rc = selinux_set_mnt_opts(sb, mc->security, 0, NULL);
> + if (rc)
> + return rc;
> +
> + /* Allow all mounts performed by the kernel */
> + if (mc->ms_flags & MS_KERNMOUNT)
> + return 0;
> +
> + ad.type = LSM_AUDIT_DATA_DENTRY;
> + ad.u.dentry = sb->s_root;
> + rc = superblock_has_perm(cred, sb, FILESYSTEM__MOUNT, &ad);
> + if (rc < 0)
> + mc->error = "SELinux: Mount of superblock not permitted";
> + return rc;
> +}
> +
> /* inode security operations */
>
> static int selinux_inode_alloc_security(struct inode *inode)
> @@ -6131,6 +6304,12 @@ static struct security_hook_list selinux_hooks[] = {
> LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),
> LSM_HOOK_INIT(bprm_secureexec, selinux_bprm_secureexec),
>
> + LSM_HOOK_INIT(mount_ctx_alloc, selinux_mount_ctx_alloc),
> + LSM_HOOK_INIT(mount_ctx_dup, selinux_mount_ctx_dup),
> + LSM_HOOK_INIT(mount_ctx_free, selinux_mount_ctx_free),
> + LSM_HOOK_INIT(mount_ctx_option, selinux_mount_ctx_option),
> + LSM_HOOK_INIT(mount_ctx_kern_mount, selinux_mount_ctx_kern_mount),
> +
> LSM_HOOK_INIT(sb_alloc_security, selinux_sb_alloc_security),
> LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
> LSM_HOOK_INIT(sb_copy_data, selinux_sb_copy_data),
>
Whew, big patch. It all looks fairly sane at first glance though and
it's well documented AFAICT. It would be nice if this were in more
easily digestible chunks, but I don't see how to break it up right
offhand.
--
Jeff Layton <jlayton@...chiereds.net>
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