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Message-Id: <20240814114034.113953-10-aleksandr.mikhalitsyn@canonical.com>
Date: Wed, 14 Aug 2024 13:40:34 +0200
From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To: mszeredi@...hat.com
Cc: brauner@...nel.org,
stgraber@...raber.org,
linux-fsdevel@...r.kernel.org,
Seth Forshee <sforshee@...nel.org>,
Miklos Szeredi <miklos@...redi.hu>,
Amir Goldstein <amir73il@...il.com>,
Bernd Schubert <bschubert@....com>,
Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH v2 9/9] fs/fuse: allow idmapped mounts
Now we have everything in place and we can allow idmapped mounts
by setting the FS_ALLOW_IDMAP flag. Notice that real availability
of idmapped mounts will depend on the fuse daemon. Fuse daemon
have to set FUSE_ALLOW_IDMAP flag in the FUSE_INIT reply.
To discuss:
- we enable idmapped mounts support only if "default_permissions" mode is enabled,
because otherwise we would need to deal with UID/GID mappings in the userspace side OR
provide the userspace with idmapped req->in.h.uid/req->in.h.gid values which is not
something that we probably want to. Idmapped mounts phylosophy is not about faking
caller uid/gid.
- We have a small offlist discussion with Christian around adding fs_type->allow_idmap
hook. Christian pointed that it would be nice to have a superblock flag instead like
SB_I_NOIDMAP and we can set this flag during mount time if we see that filesystem does not
support idmappings. But, unfortunately I didn't succeed here because the kernel will
know if the filesystem supports idmapping or not after FUSE_INIT request, but FUSE_INIT request
is being sent at the end of mounting process, so mount and superblock will exist and
visible by the userspace in that time. It seems like setting SB_I_NOIDMAP flag in this
case is too late as user may do the trick with creating a idmapped mount while it wasn't
restricted by SB_I_NOIDMAP. Alternatively, we can introduce a "positive" version SB_I_ALLOWIDMAP
and "weak" version of FS_ALLOW_IDMAP like FS_MAY_ALLOW_IDMAP. So if FS_MAY_ALLOW_IDMAP is set,
then SB_I_ALLOWIDMAP has to be set on the superblock to allow creation of an idmapped mount.
But that's a matter of our discussion.
Some extra links and examples:
- libfuse support
https://github.com/mihalicyn/libfuse/commits/idmap_support
- fuse-overlayfs support:
https://github.com/mihalicyn/fuse-overlayfs/commits/idmap_support
- cephfs-fuse conversion example
https://github.com/mihalicyn/ceph/commits/fuse_idmap
- glusterfs conversion example
https://github.com/mihalicyn/glusterfs/commits/fuse_idmap
Cc: Christian Brauner <brauner@...nel.org>
Cc: Seth Forshee <sforshee@...nel.org>
Cc: Miklos Szeredi <miklos@...redi.hu>
Cc: Amir Goldstein <amir73il@...il.com>
Cc: Bernd Schubert <bschubert@....com>
Cc: <linux-fsdevel@...r.kernel.org>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
---
fs/fuse/fuse_i.h | 3 +++
fs/fuse/inode.c | 13 ++++++++++---
include/uapi/linux/fuse.h | 5 ++++-
3 files changed, 17 insertions(+), 4 deletions(-)
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 883151a44d72..b2780ab59069 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -848,6 +848,9 @@ struct fuse_conn {
/* Add owner_{u,g}id info when creating a new inode */
unsigned int owner_uid_gid_ext:1;
+ /* Allow creation of idmapped mounts */
+ unsigned int allow_idmap:1;
+
/* Does the filesystem support per inode DAX? */
unsigned int inode_dax:1;
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 6c205731c844..ed4c2688047f 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1345,6 +1345,12 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
fm->sb->s_export_op = &fuse_export_fid_operations;
if (flags & FUSE_OWNER_UID_GID_EXT)
fc->owner_uid_gid_ext = 1;
+ if (flags & FUSE_ALLOW_IDMAP) {
+ if (fc->owner_uid_gid_ext && fc->default_permissions)
+ fc->allow_idmap = 1;
+ else
+ ok = false;
+ }
} else {
ra_pages = fc->max_read / PAGE_SIZE;
fc->no_lock = 1;
@@ -1392,7 +1398,8 @@ void fuse_send_init(struct fuse_mount *fm)
FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_EXT | FUSE_INIT_EXT |
FUSE_SECURITY_CTX | FUSE_CREATE_SUPP_GROUP |
FUSE_HAS_EXPIRE_ONLY | FUSE_DIRECT_IO_ALLOW_MMAP |
- FUSE_NO_EXPORT_SUPPORT | FUSE_HAS_RESEND | FUSE_OWNER_UID_GID_EXT;
+ FUSE_NO_EXPORT_SUPPORT | FUSE_HAS_RESEND | FUSE_OWNER_UID_GID_EXT |
+ FUSE_ALLOW_IDMAP;
#ifdef CONFIG_FUSE_DAX
if (fm->fc->dax)
flags |= FUSE_MAP_ALIGNMENT;
@@ -1981,7 +1988,7 @@ static void fuse_kill_sb_anon(struct super_block *sb)
static struct file_system_type fuse_fs_type = {
.owner = THIS_MODULE,
.name = "fuse",
- .fs_flags = FS_HAS_SUBTYPE | FS_USERNS_MOUNT,
+ .fs_flags = FS_HAS_SUBTYPE | FS_USERNS_MOUNT | FS_ALLOW_IDMAP,
.init_fs_context = fuse_init_fs_context,
.parameters = fuse_fs_parameters,
.kill_sb = fuse_kill_sb_anon,
@@ -2002,7 +2009,7 @@ static struct file_system_type fuseblk_fs_type = {
.init_fs_context = fuse_init_fs_context,
.parameters = fuse_fs_parameters,
.kill_sb = fuse_kill_sb_blk,
- .fs_flags = FS_REQUIRES_DEV | FS_HAS_SUBTYPE,
+ .fs_flags = FS_REQUIRES_DEV | FS_HAS_SUBTYPE | FS_ALLOW_IDMAP,
};
MODULE_ALIAS_FS("fuseblk");
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index d9ecc17fd13b..b23e8247ce43 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -221,6 +221,7 @@
* 7.41
* - add FUSE_EXT_OWNER_UID_GID
* - add FUSE_OWNER_UID_GID_EXT
+ * - add FUSE_ALLOW_IDMAP
*/
#ifndef _LINUX_FUSE_H
@@ -256,7 +257,7 @@
#define FUSE_KERNEL_VERSION 7
/** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 40
+#define FUSE_KERNEL_MINOR_VERSION 41
/** The node ID of the root inode */
#define FUSE_ROOT_ID 1
@@ -427,6 +428,7 @@ struct fuse_file_lock {
* of the request ID indicates resend requests
* FUSE_OWNER_UID_GID_EXT: add inode owner UID/GID info to create, mkdir,
* symlink and mknod
+ * FUSE_ALLOW_IDMAP: allow creation of idmapped mounts
*/
#define FUSE_ASYNC_READ (1 << 0)
#define FUSE_POSIX_LOCKS (1 << 1)
@@ -473,6 +475,7 @@ struct fuse_file_lock {
/* Obsolete alias for FUSE_DIRECT_IO_ALLOW_MMAP */
#define FUSE_DIRECT_IO_RELAX FUSE_DIRECT_IO_ALLOW_MMAP
#define FUSE_OWNER_UID_GID_EXT (1ULL << 40)
+#define FUSE_ALLOW_IDMAP (1ULL << 41)
/**
* CUSE INIT request/reply flags
--
2.34.1
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