Bug 1297475 (CVE-2016-0728)

Summary: CVE-2016-0728 kernel: Possible use-after-free vulnerability in keyring facility
Product: [Other] Security Response Reporter: Adam Mariš <amaris>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: agordeev, ajb, alexander.strachan, alwin.warringa, anazmy, aquini, baumanmo, bhu, blc, ctowsley, dgross, dhoward, dhowells, didier.fabert, emilovanov, eric.eisenhart, esammons, fche, fdeutsch, fhrbata, gagriogi, gbailey, gnaik, hannsj_uhl, hartsjc, iboverma, jaeshin, james.eckersall, jkacur, joelsmith, jonathan.moore, jross, jsmith.fedora, kernel-mgr, kstutsma, leon, lgoncalv, liko, lwang, marcvanwageningen, matt, mcressma, mdshaikh, mguzik, mlangsdo, mmilgram, mschena, mszpak, nmurray, pdwyer, pholasek, pim, plougher, pmatouse, rcernin, redhat, riehecky, rik.theys, rvdwees, rvrbovsk, scolebrook, security-response-team, slawomir, slong, swat, syangsao, tadej.j, t.h.amundsen, timm2k, toracat, tru, vchepkov, williams, wliu, wmealing, yozone
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Fixed In Version: Doc Type: Bug Fix
Doc Text:
A use-after-free flaw was found in the way the Linux kernel's key management subsystem handled keyring object reference counting in certain error path of the join_session_keyring() function. A local, unprivileged user could use this flaw to escalate their privileges on the system.
Story Points: ---
Clone Of: Environment:
Last Closed: 2016-01-29 13:49:29 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Bug Depends On: 1296623, 1298035, 1298036, 1298037, 1298038, 1298039, 1298040, 1298931    
Bug Blocks: 1297482    
Description Flags
prototype systemtap band-aid mk. e
Proposed patch none

Description Adam Mariš 2016-01-11 15:42:09 UTC
It was reported that possible use-after-free vulnerability in keyring facility, possibly leading to local privilege escalation, was found. Function join_session_keyring in security/keys/process_keys.c holds a reference to the requested keyring, but if that keyring is the same as the one being currently used by the process, the kernel wouldn't decrease keyring->usage before returning to userspace. The usage field can be possibly overflowed causing use-after-free on the keyring object.

Introduced by:


Red Hat KCS article:

Upstream patch:

Comment 5 Wade Mealing 2016-01-13 04:49:43 UTC

Name: the Perception Point research team

Comment 6 Wade Mealing 2016-01-14 06:54:17 UTC

This issue does not affect the Linux kernels as shipped with Red Hat Enterprise Linux 5 and 6. 

Refer to https://access.redhat.com/node/2131021 for further information.

Comment 13 Frank Ch. Eigler 2016-01-19 17:25:15 UTC
Created attachment 1116284 [details]
prototype systemtap band-aid mk. e

Further investigation with larger versions of the systemtap band-aid script suggest that the larger exploit manages somehow to increment the key refcount by 2 (!!) per iteration - one of which the stap band-aid does successfully roll back.

The smaller exploit increments it by 1 per iteration, so after the band-aid application, the visible /proc/keys refcount stays static.

Comment 15 Frank Ch. Eigler 2016-01-19 19:52:32 UTC
Further experiments with the systemtap band-aid from comment #13 indicate:

- fedora22 4.2.6-200.fc22.x86_64: stap band-aid works for both exploits
  (refcounts on /proc/keys fluctuates up & down during big exploit, within
  reasonable O(10000) ranges, then keyring is gc'd at exploit interrupt)

- git linux + patch, no stap band-aid: identical behaviour

- rhel7 3.10.0-327.4.4.el7.x86_64: stap band-aid works for both exploits,
  identical behaviour

I can't explain my previous observations in comment #11; am suspecting
that the rhel7 VM being tested was already subtly corrupted during prior
testing.  The new results are post-reboot.

So, this appears to provide protection:

# debuginfo-install kernel     (or equivalent)
# stap -vgt -Gfix_p=1 -Gtrace_p=0 cve20160728e.stp

Comment 17 Wade Mealing 2016-01-20 09:53:22 UTC
Created attachment 1116563 [details]
Proposed patch

Comment 24 Vincent Danen 2016-01-21 16:50:53 UTC
External References:


Comment 25 errata-xmlrpc 2016-01-25 19:14:19 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2016:0065 https://rhn.redhat.com/errata/RHSA-2016-0065.html

Comment 26 errata-xmlrpc 2016-01-25 19:28:23 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2016:0064 https://rhn.redhat.com/errata/RHSA-2016-0064.html

Comment 29 errata-xmlrpc 2016-01-26 14:00:38 UTC
This issue has been addressed in the following products:

  MRG for RHEL-6 v.2

Via RHSA-2016:0068 https://rhn.redhat.com/errata/RHSA-2016-0068.html

Comment 30 Fedora Update System 2016-01-26 18:22:11 UTC
kernel-4.3.3-303.fc23 has been pushed to the Fedora 23 stable repository. If problems still persist, please make note of it in this bug report.

Comment 31 Fedora Update System 2016-02-01 06:25:09 UTC
kernel-4.3.4-200.fc22 has been pushed to the Fedora 22 stable repository. If problems still persist, please make note of it in this bug report.

Comment 32 errata-xmlrpc 2016-02-02 17:03:15 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7.1 EUS - Server and Compute Node Only

Via RHSA-2016:0103 https://rhn.redhat.com/errata/RHSA-2016-0103.html