Bug 1428319 - (CVE-2017-2636) CVE-2017-2636 kernel: Race condition access to n_hdlc.tbuf causes double free in n_hdlc_release()
CVE-2017-2636 kernel: Race condition access to n_hdlc.tbuf causes double free...
Status: CLOSED ERRATA
Product: Security Response
Classification: Other
Component: vulnerability (Show other bugs)
unspecified
All Linux
high Severity high
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Assigned To: Red Hat Product Security
impact=important,public=20170307,repo...
: Security
Depends On: 1429918 1429920 1429922 1431124 1431135 1429917 1429919 1429921 1429923 1430049 1431120 1431121 1431123 1431125 1431126 1431127
Blocks: 1428323
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Reported: 2017-03-02 05:06 EST by Adam Mariš
Modified: 2017-05-16 23:18 EDT (History)
30 users (show)

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Doc Text:
A race condition flaw was found in the N_HLDC Linux kernel driver when accessing n_hdlc.tbuf list that can lead to double free. A local, unprivileged user able to set the HDLC line discipline on the tty device could use this flaw to increase their privileges on the system.
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Environment:
Last Closed: 2017-05-16 23:18:45 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description Adam Mariš 2017-03-02 05:06:46 EST
A race condition flaw was found in the N_HLDC Linux kernel driver when accessing n_hdlc.tbuf that can lead to double free.

A local, unprivileged user able to set the HDLC line discipline on the tty device could use this flaw to increase their privileges on the system.
Comment 2 Adam Mariš 2017-03-02 05:29:34 EST
Acknowledgments:

Name: Alexander Popov
Comment 3 Petr Matousek 2017-03-07 08:23:29 EST
Mitigation:

The  n_hdlc kernel module will be automatically loaded when an application  attempts to use the HDLC line discipline from userspace.  This module  can be prevented from being loaded by using the system-wide modprobe  rules. The following command, run as root, will prevent accidental or  intentional loading of the module.  Red Hat Product Security believe  this method is a robust method to prevent accidental loading of the  module, even by privileged users.

​# echo "install n_hdlc /bin/true" >> /etc/modprobe.d/disable-n_hdlc.conf

The  system will need to be restarted if the n_hdlc modules are already  loaded.  In most circumstances, the n_hdlc kernel modules will be unable to be unloaded if in use and while any current process using this line  discipline is required.

Exploiting this flaw does not require Microgate or SyncLink hardware to be in use.

If further assistance is needed, see this KCS article ( https://access.redhat.com/solutions/41278 ) or contact Red Hat Global Support Services.
Comment 4 Petr Matousek 2017-03-07 08:25:50 EST
Statement:

This issue does not affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 5.

This issue does affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 6, 7 and Red Hat Enterprise MRG 2. As this issue is rated as Important, it has been scheduled to be fixed in future updates for the respective releases.
Comment 8 Vincent Danen 2017-03-07 13:37:28 EST
Was noted and made public here: http://www.openwall.com/lists/oss-security/2017/03/07/6
Comment 9 Prasad J Pandit 2017-03-07 13:39:31 EST
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1430049]
Comment 16 errata-xmlrpc 2017-04-11 07:48:03 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6

Via RHSA-2017:0892 https://access.redhat.com/errata/RHSA-2017:0892
Comment 17 errata-xmlrpc 2017-04-12 06:54:59 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise MRG 2

Via RHSA-2017:0932 https://access.redhat.com/errata/RHSA-2017:0932
Comment 18 errata-xmlrpc 2017-04-12 06:57:51 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2017:0931 https://access.redhat.com/errata/RHSA-2017:0931
Comment 19 errata-xmlrpc 2017-04-12 09:39:10 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2017:0933 https://access.redhat.com/errata/RHSA-2017:0933
Comment 20 errata-xmlrpc 2017-04-18 05:50:15 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6.4 Advanced Update Support

Via RHSA-2017:0986 https://access.redhat.com/errata/RHSA-2017:0986
Comment 21 errata-xmlrpc 2017-04-25 05:57:41 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6.2 Advanced Update Support

Via RHSA-2017:1126 https://access.redhat.com/errata/RHSA-2017:1126
Comment 22 errata-xmlrpc 2017-04-25 05:58:51 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7.2 Extended Update Support

Via RHSA-2017:1125 https://access.redhat.com/errata/RHSA-2017:1125
Comment 23 errata-xmlrpc 2017-05-16 05:44:21 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6.5 Advanced Update Support
  Red Hat Enterprise Linux 6.5 Telco Extended Update Support

Via RHSA-2017:1232 https://access.redhat.com/errata/RHSA-2017:1232
Comment 24 errata-xmlrpc 2017-05-16 05:54:40 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6.7 Extended Update Support

Via RHSA-2017:1233 https://access.redhat.com/errata/RHSA-2017:1233

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