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Bug 1356471 - (CVE-2016-6213) CVE-2016-6213 kernel: Overflowing kernel mount table using shared bind mount
CVE-2016-6213 kernel: Overflowing kernel mount table using shared bind mount
Status: NEW
Product: Security Response
Classification: Other
Component: vulnerability (Show other bugs)
unspecified
All Linux
low Severity low
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Assigned To: Red Hat Product Security
impact=low,public=20160713,reported=2...
: Security
Depends On: 1322495 1356472
Blocks: 1332565 1356474
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Reported: 2016-07-14 04:09 EDT by Adam Mariš
Modified: 2018-08-28 18:07 EDT (History)
36 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
It was found that in Linux kernel the mount table expands by a power-of-two with each bind mount command. If a system is configured to allow non-privileged user to do bind mounts, or allows to do so in a container or unprivileged mount namespace, then non-privileged user is able to cause a local DoS by overflowing the mount table, which causes a deadlock for the whole system.
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RHEL 7.3 requirements from Atomic Host:
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External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2017:1842 normal SHIPPED_LIVE Important: kernel security, bug fix, and enhancement update 2017-08-01 14:22:09 EDT
Red Hat Product Errata RHSA-2017:2077 normal SHIPPED_LIVE Important: kernel-rt security, bug fix, and enhancement update 2017-08-01 14:13:37 EDT

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Description Adam Mariš 2016-07-14 04:09:18 EDT 
It was found that in Linux kernel the mount table expands by a power-of-two with each bind mount command. If a system is configured to allow non-privileged user to do bind mounts, or allows to do so in a container or unprivileged mount namespace, then non-privileged user is able to cause a local DoS by overflowing the mount table, which causes a deadlock for the whole system.

CVE request:

http://seclists.org/oss-sec/2016/q3/56

Proofs:

http://seclists.org/oss-sec/2016/q3/65

http://seclists.org/oss-sec/2016/q3/75

Discussions:

https://lkml.org/lkml/2013/6/17/143
Comment 1 Adam Mariš 2016-07-14 04:09:39 EDT 
Acknowledgments:

Name: Qian Cai (Red Hat)
Comment 2 Adam Mariš 2016-07-14 04:10:10 EDT 
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1356472]
Comment 3 Josh Boyer 2016-07-14 09:08:54 EDT 
It seems there is some debate on whether the CVE is actually something the kernel needs to fix.  I'll hold off a bit on this one.
Comment 4 Adam Mariš 2016-07-15 02:58:43 EDT 
Another reproducer using Docker:

http://seclists.org/oss-sec/2016/q3/65
Comment 5 Andrej Nemec 2016-07-18 02:55:03 EDT 
Another reproducer which doesn't use Docker, but it needs user namespaces to be enabled:

http://seclists.org/oss-sec/2016/q3/75
Comment 6 Andrew Vagin 2016-07-21 20:05:46 EDT 
I've reported this problem two years ago
https://lkml.org/lkml/2013/6/20/709
Comment 7 Kir Kolyshkin 2016-07-28 14:02:27 EDT 
(In reply to Andrew Vagin from comment #6)
> I've reported this problem two years ago
> https://lkml.org/lkml/2013/6/20/709

It's actually three years ago.
Comment 9 Vladis Dronov 2016-08-30 09:50:21 EDT 
Statement:

This issue does not affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 5, 6, 7 and MRG-2 as of now due to the absence of unprivileged mount name spaces support.

Nevertheless, the unprivileged mount name spaces might be added to a future RHEL-7 version as a supported feature, so future Linux kernel updates for the respective releases might address this issue.
Comment 10 Andrew Vagin 2016-09-01 19:00:57 EDT 
https://lkml.org/lkml/2016/8/28/269
Comment 11 errata-xmlrpc 2017-08-01 15:08:48 EDT 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2017:2077 https://access.redhat.com/errata/RHSA-2017:2077
Comment 12 errata-xmlrpc 2017-08-02 03:47:42 EDT 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2017:1842 https://access.redhat.com/errata/RHSA-2017:1842
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