Re: [PATCH] fs: fix is_mnt_ns_file()

[Jeff Layton <jlayton@kernel.org>]

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>