[PATCH] afs: Don't cross .backup mountpoint from backup volume

[Jeffrey E Altman]

On 5/24/2024 12:17 PM, David Howells wrote:
> Hi Christian,
>
> Can you pick this up, please?
>
> Thanks,
> David
> ---
> From: Marc Dionne<marc.dionne at auristor.com>
>
> afs: Don't cross .backup mountpoint from backup volume
>
> Don't cross a mountpoint that explicitly specifies a backup volume
> (target is <vol>.backup) when starting from a backup volume.
>
> It it not uncommon to mount a volume's backup directly in the volume
> itself.  This can cause tools that are not paying attention to get
> into a loop mounting the volume onto itself as they attempt to
> traverse the tree, leading to a variety of problems.
>
> This doesn't prevent the general case of loops in a sequence of
> mountpoints, but addresses a common special case in the same way
> as other afs clients.
>
> Reported-by: Jan Henrik Sylvester<jan.henrik.sylvester at uni-hamburg.de>
> Link:http://lists.infradead.org/pipermail/linux-afs/2024-May/008454.html
> Reported-by: Markus Suvanto<markus.suvanto at gmail.com>
> Link:http://lists.infradead.org/pipermail/linux-afs/2024-February/008074.html
> Signed-off-by: Marc Dionne<marc.dionne at auristor.com>
> Signed-off-by: David Howells<dhowells at redhat.com>
> Reviewed-by: Jeffrey Altman<jaltman at auristor.com>
> cc:linux-afs at lists.infradead.org
> ---
>   fs/afs/mntpt.c |    5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c
> index 97f50e9fd9eb..297487ee8323 100644
> --- a/fs/afs/mntpt.c
> +++ b/fs/afs/mntpt.c
> @@ -140,6 +140,11 @@ static int afs_mntpt_set_params(struct fs_context *fc, struct dentry *mntpt)
>   		put_page(page);
>   		if (ret < 0)
>   			return ret;
> +
> +		/* Don't cross a backup volume mountpoint from a backup volume */
> +		if (src_as->volume && src_as->volume->type == AFSVL_BACKVOL &&
> +		    ctx->type == AFSVL_BACKVOL)
> +			return -ENODEV;
>   	}
>   
>   	return 0;

Please add

   cc: stable at vger.kernel.org

when it is applied to vfs-fixes.

Thank you.

Jeffrey Altman