Files
linux/include/linux
Eric W. Biederman c50fd34e10 mnt: Add a per mount namespace limit on the number of mounts
commit d29216842a upstream.

CAI Qian <caiqian@redhat.com> pointed out that the semantics
of shared subtrees make it possible to create an exponentially
increasing number of mounts in a mount namespace.

    mkdir /tmp/1 /tmp/2
    mount --make-rshared /
    for i in $(seq 1 20) ; do mount --bind /tmp/1 /tmp/2 ; done

Will create create 2^20 or 1048576 mounts, which is a practical problem
as some people have managed to hit this by accident.

As such CVE-2016-6213 was assigned.

Ian Kent <raven@themaw.net> described the situation for autofs users
as follows:

> The number of mounts for direct mount maps is usually not very large because of
> the way they are implemented, large direct mount maps can have performance
> problems. There can be anywhere from a few (likely case a few hundred) to less
> than 10000, plus mounts that have been triggered and not yet expired.
>
> Indirect mounts have one autofs mount at the root plus the number of mounts that
> have been triggered and not yet expired.
>
> The number of autofs indirect map entries can range from a few to the common
> case of several thousand and in rare cases up to between 30000 and 50000. I've
> not heard of people with maps larger than 50000 entries.
>
> The larger the number of map entries the greater the possibility for a large
> number of active mounts so it's not hard to expect cases of a 1000 or somewhat
> more active mounts.

So I am setting the default number of mounts allowed per mount
namespace at 100,000.  This is more than enough for any use case I
know of, but small enough to quickly stop an exponential increase
in mounts.  Which should be perfect to catch misconfigurations and
malfunctioning programs.

For anyone who needs a higher limit this can be changed by writing
to the new /proc/sys/fs/mount-max sysctl.

Tested-by: CAI Qian <caiqian@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
[bwh: Backported to 4.4: adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-04-30 05:49:28 +02:00
..
2015-10-01 12:48:11 -07:00
2015-06-25 11:49:31 +03:00
2015-10-17 21:22:08 -07:00
2015-10-07 18:08:15 +01:00
2015-08-27 20:47:09 +01:00
2016-08-20 18:09:25 +02:00
2015-05-13 12:04:55 -05:00
2015-03-25 20:28:11 -04:00
2016-03-09 15:34:52 -08:00
2015-11-07 10:40:47 -07:00
2015-02-12 18:54:15 -08:00
2015-09-08 15:35:28 -07:00
2016-07-27 09:47:33 -07:00
2015-10-18 10:14:39 -07:00
2015-01-21 19:21:30 +01:00
2014-12-31 13:06:50 -05:00
2015-10-30 01:47:27 -04:00
2015-06-24 17:49:45 -07:00
2015-05-12 10:46:53 +02:00
2015-09-08 15:35:28 -07:00
2015-03-16 21:45:54 +11:00
2015-05-05 13:40:42 -06:00
2016-04-20 15:42:02 +09:00
2015-10-23 05:44:28 -07:00
2015-08-27 19:40:58 -04:00
2015-10-01 15:06:43 +02:00
2015-10-13 19:01:25 +02:00
2015-06-25 12:06:45 +02:00
2016-10-28 03:01:30 -04:00
2015-08-18 15:49:15 -07:00
2015-07-28 08:50:42 +01:00
2015-04-29 17:17:17 -05:00
2015-11-23 09:44:58 +01:00
2015-04-14 16:49:05 -07:00
2015-10-27 18:55:31 -07:00
2015-06-24 17:49:41 -07:00
2015-10-20 22:10:45 +08:00
2015-07-21 10:39:05 -07:00
2015-06-25 04:20:04 -04:00
2016-03-03 15:07:28 -08:00
2015-03-11 17:56:28 -04:00
2015-09-10 13:29:01 -07:00
2015-09-10 13:29:01 -07:00
2015-11-06 17:50:42 -08:00
2016-12-08 07:15:24 +01:00
2015-04-12 21:03:31 +02:00
2015-01-25 23:17:28 -05:00
2015-10-09 17:00:32 -04:00
2015-10-06 17:08:19 +02:00
2015-10-22 08:59:18 -07:00
2015-05-26 15:23:23 +02:00
2015-06-25 01:13:43 +02:00
2015-02-13 21:21:41 -08:00
2016-09-30 10:18:37 +02:00
2015-04-11 15:53:35 -04:00
2016-10-28 03:01:30 -04:00
2015-06-25 17:00:39 -07:00
2016-04-12 09:08:35 -07:00
2015-08-17 11:25:28 -07:00
2015-10-01 09:57:59 -07:00
2015-10-19 01:01:21 +02:00
2016-06-01 12:15:52 -07:00
2015-11-23 09:44:58 +01:00
2014-11-28 16:08:16 +01:00
2015-12-04 08:38:42 -07:00
2015-12-13 14:30:59 -08:00
2015-03-24 09:48:14 -07:00
2015-11-13 20:34:33 -05:00
2015-09-08 15:35:28 -07:00