* [PATCH AUTOSEL 6.1 12/14] add unique mount ID
[not found] <20240115232611.209265-1-sashal@kernel.org>
@ 2024-01-15 23:25 ` Sasha Levin
2024-01-16 9:04 ` Amir Goldstein
0 siblings, 1 reply; 3+ messages in thread
From: Sasha Levin @ 2024-01-15 23:25 UTC (permalink / raw)
To: linux-kernel, stable
Cc: Miklos Szeredi, Ian Kent, Christian Brauner, Sasha Levin, viro,
linux-fsdevel
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 e04a9e9e3f14..12c8e2eeda91 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;
@@ -130,6 +133,7 @@ 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 ef50573c72a2..a003e891a682 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -232,8 +232,13 @@ 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 */
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH AUTOSEL 6.1 12/14] add unique mount ID
2024-01-15 23:25 ` [PATCH AUTOSEL 6.1 12/14] add unique mount ID Sasha Levin
@ 2024-01-16 9:04 ` Amir Goldstein
2024-01-16 11:31 ` Sasha Levin
0 siblings, 1 reply; 3+ messages in thread
From: Amir Goldstein @ 2024-01-16 9:04 UTC (permalink / raw)
To: Sasha Levin
Cc: linux-kernel, stable, Miklos Szeredi, Ian Kent, Christian Brauner,
viro, linux-fsdevel
On Tue, Jan 16, 2024 at 1:46 AM Sasha Levin <sashal@kernel.org> wrote:
>
> 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.
>
Sasha,
This is a new API, not a bug fix.
Maybe AUTOSEL was triggered by the words "This is bad news for user...."?
You have also selected this to other 6.*.y kernels.
Thanks,
Amir.
> 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 e04a9e9e3f14..12c8e2eeda91 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;
> @@ -130,6 +133,7 @@ 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 ef50573c72a2..a003e891a682 100644
> --- a/fs/stat.c
> +++ b/fs/stat.c
> @@ -232,8 +232,13 @@ 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 */
>
> --
> 2.43.0
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH AUTOSEL 6.1 12/14] add unique mount ID
2024-01-16 9:04 ` Amir Goldstein
@ 2024-01-16 11:31 ` Sasha Levin
0 siblings, 0 replies; 3+ messages in thread
From: Sasha Levin @ 2024-01-16 11:31 UTC (permalink / raw)
To: Amir Goldstein
Cc: linux-kernel, stable, Miklos Szeredi, Ian Kent, Christian Brauner,
viro, linux-fsdevel
On Tue, Jan 16, 2024 at 11:04:12AM +0200, Amir Goldstein wrote:
>On Tue, Jan 16, 2024 at 1:46 AM Sasha Levin <sashal@kernel.org> wrote:
>>
>> 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.
>>
>
>Sasha,
>
>This is a new API, not a bug fix.
>Maybe AUTOSEL was triggered by the words "This is bad news for user...."?
>
>You have also selected this to other 6.*.y kernels.
Ack, I'll drop it from everywhere. Thanks!
--
Thanks,
Sasha
^ permalink raw reply [flat|nested] 3+ messages in thread
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2024-01-15 23:25 ` [PATCH AUTOSEL 6.1 12/14] add unique mount ID Sasha Levin
2024-01-16 9:04 ` Amir Goldstein
2024-01-16 11:31 ` Sasha Levin
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