[CRIU] [PATCH] mnt: don't match the wrong nested bind mount

[Andrew Vagin]

On Wed, Apr 15, 2015 at 09:00:37AM -0600, Tycho Andersen wrote:
> Andrey reported this issue and it took me a while to figure out exactly what
> might cause it. I think the comment describes it accurately, as with that
> example I end up with mountinfo on the host like:
> 
> 47 23 253:1 /root/bind1/subdir /root/bind2 rw,relatime shared:1 - ext4 /dev/disk/by-uuid/6c5a78e0-95fa-49a8-aa91-a8093d295e58 rw,data=ordered
> 48 23 253:1 /root/bind1 /root/bind3 rw,relatime shared:1 - ext4 /dev/disk/by-uuid/6c5a78e0-95fa-49a8-aa91-a8093d295e58 rw,data=ordered
> 
> Reported-by: Andrew Vagin <avagin at odin.com>
> CC: Andrew Vagin <avagin at odin.com>

Acked-by: Andrew Vagin <avagin at odin.com>

> Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> ---
>  mount.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/mount.c b/mount.c
> index 1bb2ebc..b47041d 100644
> --- a/mount.c
> +++ b/mount.c
> @@ -674,6 +674,20 @@ static struct mount_info *find_best_external_match(struct mount_info *list, stru
>  		if (!mounts_equal(info, it, true))
>  			continue;
>  
> +		/*
> +		 * This means we have a situation like:
> +		 *
> +		 * root at criu:~# mount --bind bind1/subdir/ bind2
> +		 * root at criu:~# mount --bind bind1/ bind3
> +		 *
> +		 * outside the container, and bind1 is directly bind mounted
> +		 * inside the container. mounts_equal() considers these mounts
> +		 * equal for bind purposes, but their roots are different, and
> +		 * we want to match the one with the right root.
> +		 */
> +		if (!issubpath(info->root, it->root))
> +			continue;
> +
>  		candidate = it;
>  
>  		/*
> -- 
> 2.1.4
>