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Date: Fri, 20 Apr 2012 02:06:48 -0700
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Marcus Meissner <meissner@...e.de>
Cc: oss-security@...ts.openwall.com, Eugene Teo <eugeneteo@...nel.sg>, "security\@kernel.org" <security@...nel.org>, Sukadev Bhattiprolu <sukadev@...ibm.com>, Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: Re: CVE request: pid namespace leak in kernel 3.0 and 3.1
Marcus Meissner <meissner@...e.de> writes:
> On Fri, Apr 20, 2012 at 09:14:58AM +0400, Pavel Emelyanov wrote:
>> On 04/20/2012 07:10 AM, Eugene Teo wrote:
>> >> So we know what is holding the pid namespace reference.
>> >>
>> >> Additional thoughts.
>> >>
>> >> Does echo 3 > /proc/sys/vm/drop_caches clear up the issue?
>> >
>> > No.
>> >
>> >> Is there a corresponding task_struct leak?
>> >
>> > Yes.
>> >
>> >> I don't have much of a clue or much concern as this seems fixed in later kernels but I am happy to suggest things to look for to help narrow this down.
>> >
>> > I'm helping to provide more information.
>>
>> Is there also a vfsmount struct leak as well? The pidns creating implies
>> kern-mount-ing of a proc and it should be released when child reaper of
>> the namespace dies.
>
> Yes, apparently (mnt_cache jumps 2*tries).
The other mnt_cache entry looks like the internal mount for the ipc
mqueue superblock/namespace.
> I diffed slabinfo before and after approx 7500 tries on a freshly rebooted machine (3.1.10), here
> are the suspicious large jumps:
Hmm. This smells like unreaped zombies, we will drop the mounts from at
least the pid namespace in release_task -> proc_flush_task which you
can't avoid if you get as far as release_task(), and release_task
is the guts of the zombie reaper. If the mounts still exist the
processes should still be visible in /proc.
Is this really steady state data? Have the zombies really been reaped?
Perhaps there is a signal deliver bug to init where it isn't noticing it
has re parented children?
Otherwise these numbers should change and go down as processes are
reaped and we can get a clue about where the bug is by looking at what
has leaked.
> -mqueue_inode_cache 1 4 896 4 1 : tunables 54 27 0 : slabdata 1 1 0
> +mqueue_inode_cache 7516 7516 896 4 1 : tunables 54 27 0 : slabdata 1879 1879 0
>
> -pid_namespace 0 0 2112 3 2 : tunables 24 12 0 : slabdata 0 0 0
> +pid_namespace 7515 7515 2112 3 2 : tunables 24 12 0 : slabdata 2505 2505 0
>
> -proc_inode_cache 591 696 632 6 1 : tunables 54 27 0 : slabdata 116 116 0
> +proc_inode_cache 8105 8124 632 6 1 : tunables 54 27 0 : slabdata 1352 1354 0
>
> -mnt_cache 45 45 256 15 1 : tunables 120 60 0 : slabdata 3 3 0
> +mnt_cache 15077 15090 256 15 1 : tunables 120 60 0 : slabdata 1006 1006 0
>
> -dentry 10840 10840 192 20 1 : tunables 120 60 0 : slabdata 542 542 0
> +dentry 26780 26880 192 20 1 : tunables 120 60 0 : slabdata 1343 1344 0
>
> -size-4096 59 59 4096 1 1 : tunables 24 12 0 : slabdata 59 59 0
> +size-4096 7577 7577 4096 1 1 : tunables 24 12 0 : slabdata 7577 7577 0
> -size-1024 665 680 1024 4 1 : tunables 54 27 0 : slabdata 170 170 0
> +size-1024 15700 15700 1024 4 1 : tunables 54 27 0 : slabdata 3925 3925 0
> -size-64 3360 3540 64 59 1 : tunables 120 60 0 : slabdata 60 60 0
> +size-64 15097 22597 64 59 1 : tunables 120 60 0 : slabdata 383 383 0
> -size-32 7892 7952 32 112 1 : tunables 120 60 0 : slabdata 71 71 0
> +size-32 23920 31472 32 112 1 : tunables 120 60 0 : slabdata 281 281 0
I hate to say it but it looks very much to me like I am looking at data
for unreaped zombies.
Eric
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