[PATCH] fs: fix is_mnt_ns_file()

[PATCH] fs: fix is_mnt_ns_file()

[Miklos Szeredi]

Commit 1fa08aece425 ("nsfs: convert to path_from_stashed() helper") reused
nsfs dentry's d_fsdata, which no longer contains a pointer to
proc_ns_operations.

Fix the remaining use in is_mnt_ns_file().

Fixes: 1fa08aece425 ("nsfs: convert to path_from_stashed() helper")
Cc: <stable@vger.kernel.org> # v6.9
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---

Came across this while getting the mnt_ns in fsnotify_mark(), tested the
fix in that context.  I don't have a test for mainline, though.

 fs/namespace.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 23e81c2a1e3f..6eec7794f707 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2055,9 +2055,15 @@ SYSCALL_DEFINE1(oldumount, char __user *, name)
 
 static bool is_mnt_ns_file(struct dentry *dentry)
 {
+	struct ns_common *ns;
+
 	/* Is this a proxy for a mount namespace? */
-	return dentry->d_op == &ns_dentry_operations &&
-	       dentry->d_fsdata == &mntns_operations;
+	if (dentry->d_op != &ns_dentry_operations)
+		return false;
+
+	ns = d_inode(dentry)->i_private;
+
+	return ns->ops == &mntns_operations;
 }
 
 struct ns_common *from_mnt_ns(struct mnt_namespace *mnt)
-- 
2.47.0

Re: [PATCH] fs: fix is_mnt_ns_file()

[Jeff Layton]

On Wed, 2024-12-11 at 13:11 +0100, Miklos Szeredi wrote:
> Commit 1fa08aece425 ("nsfs: convert to path_from_stashed() helper") reused
> nsfs dentry's d_fsdata, which no longer contains a pointer to
> proc_ns_operations.
>
> Fix the remaining use in is_mnt_ns_file().
> 
> Fixes: 1fa08aece425 ("nsfs: convert to path_from_stashed() helper")
> Cc: <stable@vger.kernel.org> # v6.9
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> ---
> 
> Came across this while getting the mnt_ns in fsnotify_mark(), tested the
> fix in that context.  I don't have a test for mainline, though.
> 
>  fs/namespace.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 23e81c2a1e3f..6eec7794f707 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -2055,9 +2055,15 @@ SYSCALL_DEFINE1(oldumount, char __user *, name)
>  
>  static bool is_mnt_ns_file(struct dentry *dentry)
>  {
> +	struct ns_common *ns;
> +
>  	/* Is this a proxy for a mount namespace? */
> -	return dentry->d_op == &ns_dentry_operations &&
> -	       dentry->d_fsdata == &mntns_operations;
> +	if (dentry->d_op != &ns_dentry_operations)
> +		return false;
> +
> +	ns = d_inode(dentry)->i_private;
> +
> +	return ns->ops == &mntns_operations;
>  }
>  
>  struct ns_common *from_mnt_ns(struct mnt_namespace *mnt)

Took me a min to figure out how i_private gets set, but this looks
correct.

Reviewed-by: Jeff Layton <jlayton@kernel.org>

Re: [PATCH] fs: fix is_mnt_ns_file()

[Al Viro]

On Wed, Dec 11, 2024 at 01:11:17PM +0100, Miklos Szeredi wrote:
> Commit 1fa08aece425 ("nsfs: convert to path_from_stashed() helper") reused
> nsfs dentry's d_fsdata, which no longer contains a pointer to
> proc_ns_operations.

Acked-by: Al Viro <viro@zeniv.linux.org.uk>

Re: [PATCH] fs: fix is_mnt_ns_file()

[Christian Brauner]

On Wed, 11 Dec 2024 13:11:17 +0100, Miklos Szeredi wrote:
> Commit 1fa08aece425 ("nsfs: convert to path_from_stashed() helper") reused
> nsfs dentry's d_fsdata, which no longer contains a pointer to
> proc_ns_operations.
> 
> Fix the remaining use in is_mnt_ns_file().
> 
> 
> [...]

Thanks for fixing that!

---

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] fs: fix is_mnt_ns_file()
      https://git.kernel.org/vfs/vfs/c/aa21f333c86c