Message-ID: <156173685496.14728.9606180227161368035.stgit@warthog.procyon.org.uk>
Date:   Fri, 28 Jun 2019 16:47:35 +0100
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     dhowells@...hat.com, raven@...maw.net, mszeredi@...hat.com,
        christian@...uner.io, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 4/6] vfs: Allow mount information to be queried by fsinfo()
 [ver #15]

Allow mount information, including information about the topology tree to
be queried with the fsinfo() system call.  Usage of AT_FSINFO_MOUNTID_PATH
allows overlapping mounts to be queried.

To this end, four fsinfo() attributes are provided:

 (1) FSINFO_ATTR_MOUNT_INFO.

     This is a structure providing information about a mount, including:

	- Mounted superblock ID.
	- Mount ID (as AT_FSINFO_MOUNTID_PATH).
	- Parent mount ID.
	- Mount attributes (eg. R/O, NOEXEC).
	- A change counter.

     Note that the parent mount ID is overridden to the ID of the queried
     mount if the parent lies outside of the chroot or dfd tree.

 (2) FSINFO_ATTR_MOUNT_DEVNAME.

     This a string providing the device name associated with the mount.

     Note that the device name may be a path that lies outside of the root.

 (3) FSINFO_ATTR_MOUNT_CHILDREN.

     This produces an array of structures, one for each child and capped
     with one for the argument mount (checked after listing all the
     children).  Each element contains the mount ID and the change counter
     of the respective mount object.

 (4) FSINFO_ATTR_MOUNT_SUBMOUNT.

     This is a 1D array of strings, indexed with struct fsinfo_params::Nth.
     Each string is the relative pathname of the corresponding child
     returned by FSINFO_ATTR_MOUNT_CHILDREN.

     Note that paths in the mount at the base of the tree (whether that be
     dfd or chroot) are relative to the base of the tree, not the root
     directory of that mount.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/d_path.c                 |    2 
 fs/fsinfo.c                 |    8 ++
 fs/internal.h               |    9 ++
 fs/namespace.c              |  177 +++++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/fsinfo.h |   28 +++++++
 samples/vfs/test-fsinfo.c   |   47 +++++++++++
 6 files changed, 267 insertions(+), 4 deletions(-)

diff --git a/fs/d_path.c b/fs/d_path.c
index e8fce6b1174f..71b3e8cd79b8 100644
--- a/fs/d_path.c
+++ b/fs/d_path.c
@@ -227,7 +227,7 @@ static int prepend_unreachable(char **buffer, int *buflen)
 	return prepend(buffer, buflen, "(unreachable)", 13);
 }
 
-static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
+void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
 {
 	unsigned seq;
 
diff --git a/fs/fsinfo.c b/fs/fsinfo.c
index aee7fedace19..758d1cbf8eba 100644
--- a/fs/fsinfo.c
+++ b/fs/fsinfo.c
@@ -353,6 +353,10 @@ int generic_fsinfo(struct path *path, struct fsinfo_kparams *params)
 	case _genf(PARAM_SPECIFICATION,	param_specification);
 	case _genf(PARAM_ENUM,		param_enum);
 	case _genp(PARAMETERS,		parameters);
+	case _genp(MOUNT_INFO,		mount_info);
+	case _genp(MOUNT_DEVNAME,	mount_devname);
+	case _genp(MOUNT_CHILDREN,	mount_children);
+	case _genp(MOUNT_SUBMOUNT,	mount_submount);
 	default:
 		return -EOPNOTSUPP;
 	}
@@ -637,6 +641,10 @@ static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
 	FSINFO_STRING_N		(SERVER_NAME),
 	FSINFO_STRUCT_NM	(SERVER_ADDRESS,	server_address),
 	FSINFO_STRING		(AFS_CELL_NAME),
+	FSINFO_STRUCT		(MOUNT_INFO,		mount_info),
+	FSINFO_STRING		(MOUNT_DEVNAME),
+	FSINFO_STRUCT_ARRAY	(MOUNT_CHILDREN,	mount_child),
+	FSINFO_STRING_N		(MOUNT_SUBMOUNT),
 };
 
 /**
diff --git a/fs/internal.h b/fs/internal.h
index d5283a55b25d..d75bdd97cdd9 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -52,6 +52,11 @@ void __generic_write_end(struct inode *inode, loff_t pos, unsigned copied,
  */
 extern void __init chrdev_init(void);
 
+/*
+ * d_path.c
+ */
+extern void get_fs_root_rcu(struct fs_struct *fs, struct path *root);
+
 /*
  * fs_context.c
  */
@@ -97,6 +102,10 @@ extern void __mnt_drop_write_file(struct file *);
 
 extern void dissolve_on_fput(struct vfsmount *);
 extern int lookup_mount_object(struct path *, int, struct path *);
+extern int fsinfo_generic_mount_info(struct path *, struct fsinfo_kparams *);
+extern int fsinfo_generic_mount_devname(struct path *, struct fsinfo_kparams *);
+extern int fsinfo_generic_mount_children(struct path *, struct fsinfo_kparams *);
+extern int fsinfo_generic_mount_submount(struct path *, struct fsinfo_kparams *);
 
 /*
  * fs_struct.c
diff --git a/fs/namespace.c b/fs/namespace.c
index c306e9362604..925602b8c329 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -29,6 +29,7 @@
 #include <linux/sched/task.h>
 #include <uapi/linux/mount.h>
 #include <linux/fs_context.h>
+#include <linux/fsinfo.h>
 
 #include "pnode.h"
 #include "internal.h"
@@ -4108,3 +4109,179 @@ int lookup_mount_object(struct path *root, int mnt_id, struct path *_mntpt)
 	unlock_mount_hash();
 	goto out_unlock;
 }
+
+#ifdef CONFIG_FSINFO
+int fsinfo_generic_mount_info(struct path *path, struct fsinfo_kparams *params)
+{
+	struct fsinfo_mount_info *p = params->buffer;
+	struct super_block *sb;
+	struct mount *m;
+	struct path root;
+	unsigned int flags;
+
+	if (!path->mnt)
+		return -ENODATA;
+
+	m = real_mount(path->mnt);
+	sb = m->mnt.mnt_sb;
+
+	p->f_sb_id		= sb->s_unique_id;
+	p->mnt_id		= m->mnt_id;
+	p->parent_id		= m->mnt_parent->mnt_id;
+	p->change_counter	= atomic_read(&m->mnt_change_counter);
+
+	get_fs_root(current->fs, &root);
+	if (path->mnt == root.mnt) {
+		p->parent_id = p->mnt_id;
+	} else {
+		rcu_read_lock();
+		if (!are_paths_connected(&root, path))
+			p->parent_id = p->mnt_id;
+		rcu_read_unlock();
+	}
+	if (IS_MNT_SHARED(m))
+		p->group_id = m->mnt_group_id;
+	if (IS_MNT_SLAVE(m)) {
+		int master = m->mnt_master->mnt_group_id;
+		int dom = get_dominating_id(m, &root);
+		p->master_id = master;
+		if (dom && dom != master)
+			p->from_id = dom;
+	}
+	path_put(&root);
+
+	flags = READ_ONCE(m->mnt.mnt_flags);
+	if (flags & MNT_READONLY)
+		p->attr |= MOUNT_ATTR_RDONLY;
+	if (flags & MNT_NOSUID)
+		p->attr |= MOUNT_ATTR_NOSUID;
+	if (flags & MNT_NODEV)
+		p->attr |= MOUNT_ATTR_NODEV;
+	if (flags & MNT_NOEXEC)
+		p->attr |= MOUNT_ATTR_NOEXEC;
+	if (flags & MNT_NODIRATIME)
+		p->attr |= MOUNT_ATTR_NODIRATIME;
+
+	if (flags & MNT_NOATIME)
+		p->attr |= MOUNT_ATTR_NOATIME;
+	else if (flags & MNT_RELATIME)
+		p->attr |= MOUNT_ATTR_RELATIME;
+	else
+		p->attr |= MOUNT_ATTR_STRICTATIME;
+	return sizeof(*p);
+}
+
+int fsinfo_generic_mount_devname(struct path *path, struct fsinfo_kparams *params)
+{
+	struct mount *m;
+	size_t len;
+
+	if (!path->mnt)
+		return -ENODATA;
+
+	m = real_mount(path->mnt);
+	len = strlen(m->mnt_devname);
+	memcpy(params->buffer, m->mnt_devname, len);
+	return len;
+}
+
+/*
+ * Store a mount record into the fsinfo buffer.
+ */
+static void store_mount_fsinfo(struct fsinfo_kparams *params,
+			       struct fsinfo_mount_child *child)
+{
+	unsigned int usage = params->usage;
+	unsigned int total = sizeof(*child);
+
+	if (params->usage >= INT_MAX)
+		return;
+	params->usage = usage + total;
+	if (params->buffer && params->usage <= params->buf_size)
+		memcpy(params->buffer + usage, child, total);
+}
+
+/*
+ * Return information about the submounts relative to path.
+ */
+int fsinfo_generic_mount_children(struct path *path, struct fsinfo_kparams *params)
+{
+	struct fsinfo_mount_child record;
+	struct mount *m, *child;
+
+	if (!path->mnt)
+		return -ENODATA;
+
+	m = real_mount(path->mnt);
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(child, &m->mnt_mounts, mnt_child) {
+		if (child->mnt_parent != m)
+			continue;
+		record.mnt_id = child->mnt_id;
+		record.change_counter = atomic_read(&child->mnt_change_counter);
+		store_mount_fsinfo(params, &record);
+	}
+	rcu_read_unlock();
+
+	/* End the list with a copy of the parameter mount's details so that
+	 * userspace can quickly check for changes.
+	 */
+	record.mnt_id = m->mnt_id;
+	record.change_counter = atomic_read(&m->mnt_change_counter);
+	store_mount_fsinfo(params, &record);
+	return params->usage;
+}
+
+/*
+ * Return the path of the Nth submount relative to path.  This is derived from
+ * d_path(), but the root determination is more complicated.
+ */
+int fsinfo_generic_mount_submount(struct path *path, struct fsinfo_kparams *params)
+{
+	struct mountpoint *mp;
+	struct mount *m, *child;
+	struct path mountpoint, root;
+	unsigned int n = params->Nth;
+	size_t len;
+	void *p;
+
+	if (!path->mnt)
+		return -ENODATA;
+
+	rcu_read_lock();
+
+	m = real_mount(path->mnt);
+	list_for_each_entry_rcu(child, &m->mnt_mounts, mnt_child) {
+		mp = READ_ONCE(child->mnt_mp);
+		if (child->mnt_parent != m || !mp)
+			continue;
+		if (n-- == 0)
+			goto found;
+	}
+	rcu_read_unlock();
+	return -ENODATA;
+
+found:
+	mountpoint.mnt = path->mnt;
+	mountpoint.dentry = READ_ONCE(mp->m_dentry);
+
+	get_fs_root_rcu(current->fs, &root);
+	if (root.mnt != path->mnt) {
+		root.mnt = path->mnt;
+		root.dentry = path->mnt->mnt_root;
+	}
+
+	p = __d_path(&mountpoint, &root, params->buffer, params->buf_size);
+	rcu_read_unlock();
+
+	if (IS_ERR(p))
+		return PTR_ERR(p);
+	if (!p)
+		return -EPERM;
+
+	len = (params->buffer + params->buf_size) - p;
+	memmove(params->buffer, p, len);
+	return len;
+}
+#endif /* CONFIG_FSINFO */
diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
index 58a50207256f..401ad9625c11 100644
--- a/include/uapi/linux/fsinfo.h
+++ b/include/uapi/linux/fsinfo.h
@@ -35,6 +35,10 @@ enum fsinfo_attribute {
 	FSINFO_ATTR_SERVER_NAME		= 17,	/* Name of the Nth server (string) */
 	FSINFO_ATTR_SERVER_ADDRESS	= 18,	/* Mth address of the Nth server */
 	FSINFO_ATTR_AFS_CELL_NAME	= 19,	/* AFS cell name (string) */
+	FSINFO_ATTR_MOUNT_INFO		= 20,	/* Mount object information */
+	FSINFO_ATTR_MOUNT_DEVNAME	= 21,	/* Mount object device name (string) */
+	FSINFO_ATTR_MOUNT_CHILDREN	= 22,	/* Submount list (array) */
+	FSINFO_ATTR_MOUNT_SUBMOUNT	= 23,	/* Relative path of Nth submount (string) */
 	FSINFO_ATTR__NR
 };
 
@@ -288,4 +292,28 @@ struct fsinfo_server_address {
 	struct __kernel_sockaddr_storage address;
 };
 
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_MOUNT_INFO).
+ */
+struct fsinfo_mount_info {
+	__u64		f_sb_id;	/* Superblock ID */
+	__u32		mnt_id;		/* Mount identifier (use with AT_FSINFO_MOUNTID_PATH) */
+	__u32		parent_id;	/* Parent mount identifier */
+	__u32		group_id;	/* Mount group ID */
+	__u32		master_id;	/* Slave master group ID */
+	__u32		from_id;	/* Slave propagated from ID */
+	__u32		attr;		/* MOUNT_ATTR_* flags */
+	__u32		change_counter;	/* Number of changed applied. */
+	__u32		__reserved[1];
+};
+
+/*
+ * Information struct element for fsinfo(FSINFO_ATTR_MOUNT_CHILDREN).
+ * - An extra element is placed on the end representing the parent mount.
+ */
+struct fsinfo_mount_child {
+	__u32		mnt_id;		/* Mount identifier (use with AT_FSINFO_MOUNTID_PATH) */
+	__u32		change_counter;	/* Number of changes applied to mount. */
+};
+
 #endif /* _UAPI_LINUX_FSINFO_H */
diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
index 27c4bb93c219..28c9f3cd2c8c 100644
--- a/samples/vfs/test-fsinfo.c
+++ b/samples/vfs/test-fsinfo.c
@@ -21,10 +21,10 @@
 #include <errno.h>
 #include <time.h>
 #include <math.h>
-#include <fcntl.h>
 #include <sys/syscall.h>
 #include <linux/fsinfo.h>
 #include <linux/socket.h>
+#include <linux/fcntl.h>
 #include <sys/stat.h>
 #include <arpa/inet.h>
 
@@ -86,6 +86,10 @@ static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
 	FSINFO_STRING_N		(SERVER_NAME,		server_name),
 	FSINFO_STRUCT_NM	(SERVER_ADDRESS,	server_address),
 	FSINFO_STRING		(AFS_CELL_NAME,		-),
+	FSINFO_STRUCT		(MOUNT_INFO,		mount_info),
+	FSINFO_STRING		(MOUNT_DEVNAME,		mount_devname),
+	FSINFO_STRUCT_ARRAY	(MOUNT_CHILDREN,	mount_child),
+	FSINFO_STRING_N		(MOUNT_SUBMOUNT,	mount_submount),
 };
 
 #define FSINFO_NAME(X,Y) [FSINFO_ATTR_##X] = #Y
@@ -110,6 +114,10 @@ static const char *fsinfo_attr_names[FSINFO_ATTR__NR] = {
 	FSINFO_NAME		(SERVER_NAME,		server_name),
 	FSINFO_NAME		(SERVER_ADDRESS,	server_address),
 	FSINFO_NAME		(AFS_CELL_NAME,		afs_cell_name),
+	FSINFO_NAME		(MOUNT_INFO,		mount_info),
+	FSINFO_NAME		(MOUNT_DEVNAME,		mount_devname),
+	FSINFO_NAME		(MOUNT_CHILDREN,	mount_children),
+	FSINFO_NAME		(MOUNT_SUBMOUNT,	mount_submount),
 };
 
 union reply {
@@ -123,6 +131,8 @@ union reply {
 	struct fsinfo_timestamp_info timestamps;
 	struct fsinfo_volume_uuid uuid;
 	struct fsinfo_server_address srv_addr;
+	struct fsinfo_mount_info mount_info;
+	struct fsinfo_mount_child mount_children[1];
 };
 
 static void dump_hex(unsigned int *data, int from, int to)
@@ -351,6 +361,29 @@ static void dump_attr_SERVER_ADDRESS(union reply *r, int size)
 	printf("family=%u\n", f->address.ss_family);
 }
 
+static void dump_attr_MOUNT_INFO(union reply *r, int size)
+{
+	struct fsinfo_mount_info *f = &r->mount_info;
+
+	printf("\n");
+	printf("\tsb_id   : %llx\n", (unsigned long long)f->f_sb_id);
+	printf("\tmnt_id  : %x\n", f->mnt_id);
+	printf("\tparent  : %x\n", f->parent_id);
+	printf("\tgroup   : %x\n", f->group_id);
+	printf("\tattr    : %x\n", f->attr);
+	printf("\tchanges : %x\n", f->change_counter);
+}
+
+static void dump_attr_MOUNT_CHILDREN(union reply *r, int size)
+{
+	struct fsinfo_mount_child *f = r->mount_children;
+	int i = 0;
+
+	printf("\n");
+	for (; size >= sizeof(*f); size -= sizeof(*f), f++)
+		printf("\t[%u] %8x %8x\n", i++, f->mnt_id, f->change_counter);
+}
+
 /*
  *
  */
@@ -367,6 +400,8 @@ static const dumper_t fsinfo_attr_dumper[FSINFO_ATTR__NR] = {
 	FSINFO_DUMPER(TIMESTAMP_INFO),
 	FSINFO_DUMPER(VOLUME_UUID),
 	FSINFO_DUMPER(SERVER_ADDRESS),
+	FSINFO_DUMPER(MOUNT_INFO),
+	FSINFO_DUMPER(MOUNT_CHILDREN),
 };
 
 static void dump_fsinfo(enum fsinfo_attribute attr,
@@ -569,16 +604,21 @@ int main(int argc, char **argv)
 	unsigned int attr;
 	int raw = 0, opt, Nth, Mth;
 
-	while ((opt = getopt(argc, argv, "adlr"))) {
+	while ((opt = getopt(argc, argv, "Madlr"))) {
 		switch (opt) {
+		case 'M':
+			params.at_flags = AT_FSINFO_MOUNTID_PATH;
+			continue;
 		case 'a':
 			params.at_flags |= AT_NO_AUTOMOUNT;
+			params.at_flags &= ~AT_FSINFO_MOUNTID_PATH;
 			continue;
 		case 'd':
 			debug = true;
 			continue;
 		case 'l':
 			params.at_flags &= ~AT_SYMLINK_NOFOLLOW;
+			params.at_flags &= ~AT_FSINFO_MOUNTID_PATH;
 			continue;
 		case 'r':
 			raw = 1;
@@ -591,7 +631,8 @@ int main(int argc, char **argv)
 	argv += optind;
 
 	if (argc != 1) {
-		printf("Format: test-fsinfo [-alr] <file>\n");
+		printf("Format: test-fsinfo [-adlr] <file>\n");
+		printf("Format: test-fsinfo [-dr] -M <mnt_id>\n");
 		exit(2);
 	}
 

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