Subject: bug#21372: [PATCH] df: fix prioritize real mounts over bind mounts

From: Pádraig Brady <[email-masked]>
Date: Fri, 11 Sep 2015 21:42:20 +0100

On 31/08/15 22:05, Dave Chiluk wrote:
> Fixes an issue where bind mounts with shorter mount directories than the
> original mount are prioritized when running df.  The root cause of this
> is that /proc/self/mountinfo now lists the filesystem device with bind
> mounts rather than the source directory. With /etc/mtab the source
> device was listed as the originating directory so this was not an issue.
> 
> More information is available here.
> https://bugs.launchpad.net/ubuntu/+source/coreutils/+bug/1432871
> ---
>  src/df.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/src/df.c b/src/df.c
> index 2e541b9..00c77c1 100644
> --- a/src/df.c
> +++ b/src/df.c
> @@ -652,9 +652,14 @@ filter_mount_list (bool devices_only)
>                else if ((strchr (me->me_devname, '/')
>                         /* let "real" devices with '/' in the name win.  */
>                          && ! strchr (devlist->me->me_devname, '/'))
> -                       /* let a shorter mountdir win.  */
> -                       || (strlen (devlist->me->me_mountdir)
> +                       /* let a shorter mountdir win. */
> +                       /* Only if it's not a bind mount. */
> +                       || ((strlen (devlist->me->me_mountdir)
>                             > strlen (me->me_mountdir))
> +                          && (devlist->me->me_mntroot != NULL
> +                             && me->me_mntroot != NULL
> +                             && (strlen (devlist->me->me_mntroot)
> +                                 > strlen(me->me_mntroot))))

As previously mentioned, should this be >= ?

We'll need to look at tests.
This will be quite tricky given the current
avoidance of /proc/self/mountinfo in tests.
I'll look at adding a separate test for this.

thanks,
Pádraig.