From: Miklos Szeredi <mszeredi@redhat.com>
To: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
linux-man@vger.kernel.org, linux-security-module@vger.kernel.org,
Karel Zak <kzak@redhat.com>, Ian Kent <raven@themaw.net>,
David Howells <dhowells@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <christian@brauner.io>,
Amir Goldstein <amir73il@gmail.com>,
Matthew House <mattlloydhouse@gmail.com>,
Florian Weimer <fweimer@redhat.com>,
Arnd Bergmann <arnd@arndb.de>
Subject: [PATCH v4 1/6] add unique mount ID
Date: Wed, 25 Oct 2023 16:01:59 +0200 [thread overview]
Message-ID: <20231025140205.3586473-2-mszeredi@redhat.com> (raw)
In-Reply-To: <20231025140205.3586473-1-mszeredi@redhat.com>
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>
---
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 e157efc54023..e02bc5f41c7b 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 __read_mostly;
static struct hlist_head *mountpoint_hashtable __read_mostly;
static struct kmem_cache *mnt_cache __read_mostly;
@@ -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 d43a5cc1bfa4..77878ae48a0f 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -243,8 +243,13 @@ 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 */
--
2.41.0
next prev parent reply other threads:[~2023-10-25 14:03 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-25 14:01 [PATCH v4 0/6] querying mount attributes Miklos Szeredi
2023-10-25 14:01 ` Miklos Szeredi [this message]
2023-10-25 14:02 ` [PATCH v4 2/6] mounts: keep list of mounts in an rbtree Miklos Szeredi
2023-10-27 3:11 ` Ian Kent
2023-10-27 8:17 ` Miklos Szeredi
2023-10-28 1:36 ` Ian Kent
2023-10-30 5:37 ` Ian Kent
2023-10-30 5:45 ` Ian Kent
2023-10-30 9:06 ` Miklos Szeredi
2023-10-31 1:23 ` Ian Kent
2023-10-25 14:02 ` [PATCH v4 3/6] namespace: extract show_path() helper Miklos Szeredi
2023-10-25 14:02 ` [PATCH v4 4/6] add statmount(2) syscall Miklos Szeredi
2023-11-08 2:58 ` Paul Moore
2023-11-08 7:58 ` Christian Brauner
2023-11-08 20:10 ` Paul Moore
2023-11-10 17:00 ` Paul Moore
2023-11-12 13:05 ` Christian Brauner
2023-11-12 20:29 ` Paul Moore
2023-10-25 14:02 ` [PATCH v4 5/6] add listmount(2) syscall Miklos Szeredi
2023-11-07 21:23 ` Jonathan Corbet
2023-11-08 7:53 ` Christian Brauner
2023-11-08 16:20 ` Jonathan Corbet
2023-11-08 16:23 ` Christian Brauner
2023-11-08 2:58 ` Paul Moore
2024-01-10 22:23 ` Guenter Roeck
2024-01-11 0:32 ` Linus Torvalds
2024-01-11 5:12 ` Guenter Roeck
2024-01-11 18:57 ` Guenter Roeck
2024-01-11 20:14 ` Linus Torvalds
2024-01-11 23:01 ` Arnd Bergmann
2024-01-11 23:57 ` Guenter Roeck
2024-01-12 3:40 ` Linus Torvalds
2024-01-12 5:24 ` Guenter Roeck
2024-01-12 9:00 ` Christian Brauner
2024-01-23 14:14 ` John Paul Adrian Glaubitz
2024-01-23 15:31 ` Guenter Roeck
2024-01-23 14:14 ` John Paul Adrian Glaubitz
2023-10-25 14:02 ` [PATCH v4 6/6] wire up syscalls for statmount/listmount Miklos Szeredi
2024-01-09 1:11 ` Florian Fainelli
2023-11-01 11:13 ` [PATCH v4 0/6] querying mount attributes Christian Brauner
2023-11-01 13:18 ` Miklos Szeredi
2023-11-01 15:54 ` Christian Brauner
2023-11-01 11:52 ` Ian Kent
2023-11-06 12:10 ` Karel Zak
2023-11-06 13:33 ` Amir Goldstein
2023-11-07 0:47 ` Ian Kent
2023-11-06 23:54 ` Ian Kent
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