Unverified Commit 98d2b430 authored by Miklos Szeredi's avatar Miklos Szeredi Committed by Christian Brauner
Browse files

add unique mount ID 



If a mount is released then its mnt_id can immediately be reused.  This is
bad news for user interfaces that want to uniquely identify a mount.

Implementing a unique mount ID is trivial (use a 64bit counter).
Unfortunately userspace assumes 32bit size and would overflow after the
counter reaches 2^32.

Introduce a new 64bit ID alongside the old one.  Initialize the counter to
2^32, this guarantees that the old and new IDs are never mixed up.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20231025140205.3586473-2-mszeredi@redhat.com


Reviewed-by: default avatarIan Kent <raven@themaw.net>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent b85ea95d

fs/mount.h

+2 −1
Original line number Diff line number Diff line
@@ -72,7 +72,8 @@ struct mount { 
	struct fsnotify_mark_connector __rcu *mnt_fsnotify_marks;

	__u32 mnt_fsnotify_mask;

#endif

	int mnt_id;			/* mount identifier */

	int mnt_id;			/* mount identifier, reused */

	u64 mnt_id_unique;		/* mount ID unique until reboot */

	int mnt_group_id;		/* peer group identifier */

	int mnt_expiry_mark;		/* true if marked for expiry */

	struct hlist_head mnt_pins;

fs/namespace.c

+4 −0
Original line number Diff line number Diff line
@@ -68,6 +68,9 @@ static u64 event; 
static DEFINE_IDA(mnt_id_ida);

static DEFINE_IDA(mnt_group_ida);



/* Don't allow confusion with old 32bit mount ID */

static atomic64_t mnt_id_ctr = ATOMIC64_INIT(1ULL << 32);



static struct hlist_head *mount_hashtable __ro_after_init;

static struct hlist_head *mountpoint_hashtable __ro_after_init;

static struct kmem_cache *mnt_cache __ro_after_init;
@@ -131,6 +134,7 @@ static int mnt_alloc_id(struct mount *mnt) 
	if (res < 0)

		return res;

	mnt->mnt_id = res;

	mnt->mnt_id_unique = atomic64_inc_return(&mnt_id_ctr);

	return 0;

}

fs/stat.c

+7 −2
Original line number Diff line number Diff line
@@ -243,8 +243,13 @@ static int vfs_statx(int dfd, struct filename *filename, int flags, 


	error = vfs_getattr(&path, stat, request_mask, flags);



	if (request_mask & STATX_MNT_ID_UNIQUE) {

		stat->mnt_id = real_mount(path.mnt)->mnt_id_unique;

		stat->result_mask |= STATX_MNT_ID_UNIQUE;

	} else {

		stat->mnt_id = real_mount(path.mnt)->mnt_id;

		stat->result_mask |= STATX_MNT_ID;

	}



	if (path.mnt->mnt_root == path.dentry)

		stat->attributes |= STATX_ATTR_MOUNT_ROOT;

include/uapi/linux/stat.h

+1 −0
Original line number Diff line number Diff line
@@ -154,6 +154,7 @@ struct statx { 
#define STATX_BTIME		0x00000800U	/* Want/got stx_btime */

#define STATX_MNT_ID		0x00001000U	/* Got stx_mnt_id */

#define STATX_DIOALIGN		0x00002000U	/* Want/got direct I/O alignment info */

#define STATX_MNT_ID_UNIQUE	0x00004000U	/* Want/got extended stx_mount_id */



#define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */