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: NEW
Product: Security Response
Classification: Other
Component: vulnerability (Show other bugs)
unspecified
All Linux
high Severity high
: ---
: ---
Assigned To: Red Hat Product Security
impact=important,public=20170307,repo...
: Security
Depends On: 1429917 1429918 1429919 1429920 1429921 1429922 1429923 1431120 1431121 1431123 1431124 1431125 1431126 1431127 1431135 1430049
Blocks: 1428323
  Show dependency treegraph
 
Reported: 2017-03-02 05:06 EST by Adam Mariš
Modified: 2017-03-22 01:25 EDT (History)
30 users (show)

See Also:
Fixed In Version:
Doc Type: If docs needed, set a value
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.
Story Points: ---
Clone Of:
Environment:
Last Closed:
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
CRM:
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---


Attachments (Terms of Use)

  None (edit)
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 12 Vincent Danen 2017-03-08 14:25:43 EST
External References:

https://access.redhat.com/security/vulnerabilities/CVE-2017-2636

Note You need to log in before you can comment on or make changes to this bug.