From: Miklos Szeredi mszeredi@redhat.com
[ Upstream commit 98d2b43081972abeb5bb5a087bc3e3197531c46e ]
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: Miklos Szeredi mszeredi@redhat.com Link: https://lore.kernel.org/r/20231025140205.3586473-2-mszeredi@redhat.com Reviewed-by: Ian Kent raven@themaw.net Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/mount.h | 3 ++- fs/namespace.c | 4 ++++ fs/stat.c | 9 +++++++-- include/uapi/linux/stat.h | 1 + 4 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/fs/mount.h b/fs/mount.h index 130c07c2f8d2..a14f762b3f29 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -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; diff --git a/fs/namespace.c b/fs/namespace.c index fbf0e596fcd3..0bcba81402b5 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -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; }
diff --git a/fs/stat.c b/fs/stat.c index f721d26ec3f7..d8c44c599cf2 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -247,8 +247,13 @@ static int vfs_statx(int dfd, struct filename *filename, int flags,
error = vfs_getattr(&path, stat, request_mask, flags);
- stat->mnt_id = real_mount(path.mnt)->mnt_id; - stat->result_mask |= STATX_MNT_ID; + 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; diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h index 7cab2c65d3d7..2f2ee82d5517 100644 --- a/include/uapi/linux/stat.h +++ b/include/uapi/linux/stat.h @@ -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 */