Bug 1610958 (CVE-2017-18344) - CVE-2017-18344 kernel: out-of-bounds access in the show_timer function in kernel/time/posix-timers.c
Summary: CVE-2017-18344 kernel: out-of-bounds access in the show_timer function in ker...
Status: CLOSED ERRATA
Alias: CVE-2017-18344
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
high
high
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard: impact=important,public=20171215,repo...
Keywords: Security
Depends On: 1613650 1613651 1613652 1613653 1613706 1613707 1613708 1613709 1613710 1613711 1613712 1613713 1613714 1613715 1613716 1613717 1613718 1613719
Blocks: 1618606 1610959
TreeView+ depends on / blocked
 
Reported: 2018-08-01 17:15 UTC by Laura Pardo
Modified: 2019-06-11 11:13 UTC (History)
50 users (show)

(edit)
The timer_create syscall implementation in kernel/time/posix-timers.c in the Linux kernel doesn't properly validate the sigevent->sigev_notify field, which leads to out-of-bounds access in the show_timer function.
Clone Of:
(edit)
Last Closed: 2019-06-10 10:34:56 UTC


Attachments (Terms of Use)
Disable opening of /proc/<pid>/timer file. (452 bytes, text/plain)
2018-08-08 05:56 UTC, Wade Mealing
no flags Details


External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2018:2948 None None None 2018-10-30 09:04 UTC
Red Hat Product Errata RHSA-2018:3083 None None None 2018-10-30 07:35 UTC
Red Hat Product Errata RHSA-2018:3096 None None None 2018-10-30 07:42 UTC
Red Hat Product Errata RHSA-2018:3459 None None None 2018-11-06 15:31 UTC
Red Hat Product Errata RHSA-2018:3540 None None None 2018-11-13 16:33 UTC
Red Hat Product Errata RHSA-2018:3586 None None None 2018-11-13 16:30 UTC
Red Hat Product Errata RHSA-2018:3590 None None None 2018-11-13 17:50 UTC
Red Hat Product Errata RHSA-2018:3591 None None None 2018-11-13 17:50 UTC

Description Laura Pardo 2018-08-01 17:15:30 UTC
A flaw was found in kernel versions before 4.14.8. The timer_create syscall implementation in kernel/time/posix-timers.c in the Linux kernel before 4.14.8 doesn't properly validate the sigevent->sigev_notify field, which leads to out-of-bounds access in the show_timer function (called when /proc/$PID/timers is read). This allows userspace applications to read arbitrary kernel memory (on a kernel built with CONFIG_POSIX_TIMERS and CONFIG_CHECKPOINT_RESTORE).

References:

http://seclists.org/oss-sec/2018/q3/76

An upstream patch:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cef31d9af908243421258f1df35a4a644604efbe

Comment 4 Wade Mealing 2018-08-08 05:54:28 UTC
Mitigation:

Attached to this bugzilla is a systemtap script that will prevent opening (and therefore reading) the /proc/<process>/timers file which is used to leak information.

The SystemTap script is relatively small and efficient, broken into 3 distinct sections as follows:

--------

probe kernel.function("proc_timers_open@fs/proc/base.c").return { 
        // this is -EACCES
	$return = -13;
        message = sprintf("CVE-2017-18344 mitigation denied access to %s to %s(%d)", file_name , execname(), pid());
        // print a warning message at KERN_INFO debug level
        printk(6, message);
}

probe begin {
        printk(6, "Mitigation for CVE-2017-18344 loaded.\n");
}


probe end {
        printk(6, "Mitigation for CVE-2017-18344 unloaded.\n");
}


---------

First, the script places a probe at the return of the kernel function “proc_timers_open” when called.   This modifies the return value to be EACCES which would return this value to userspace preventing this file from being opened.  When the /proc/<pid>/timer file is attempted to be opened, a message will be logged to the kernel log subsystem showing the process and pid of the application attempting to access the timer file.  

This file is not in widespread use at this time, although some applications may read from it to debug or understand their own timers that are set.  This mitigation will not be useful in this context.

Finally, the “probe begin” and “probe end” code blocks tell systemtap to add the supplied text to the kernel log buffer via the printk function. This creates an audit trail by registering in the system logs exactly when the mitigation is loaded and unloaded.  This will need to be compiled with guru mode (-g parameter) to compile.

This will need to be loaded at each boot to remain effective.  Red Hat Product security recommends updating to a patched kernel when it is available.

Red Hat always seeks to provide both mitigations to disable attacks as well as the actual patches to treat the flaw. To learn more about SystemTap, and how it can be used in your management of your Red Hat systems, please refer to Using SystemTap[1] or one of our videos about it within our Customer Portal[2].

1 - https://access.redhat.com/articles/17839
2 - https://access.redhat.com/search/#/?q=systemtap

Comment 5 Wade Mealing 2018-08-08 05:56 UTC
Created attachment 1474158 [details]
Disable opening of /proc/<pid>/timer file.

Comment 6 Wade Mealing 2018-08-08 08:10:44 UTC
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1613706]

Comment 8 Justin M. Forbes 2018-08-08 11:41:08 UTC
This was fixed for Fedora with the 4.14.8 stable kernel updates.

Comment 11 errata-xmlrpc 2018-10-30 07:35:35 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2018:3083 https://access.redhat.com/errata/RHSA-2018:3083

Comment 12 errata-xmlrpc 2018-10-30 07:41:43 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2018:3096 https://access.redhat.com/errata/RHSA-2018:3096

Comment 13 errata-xmlrpc 2018-10-30 09:04:15 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2018:2948 https://access.redhat.com/errata/RHSA-2018:2948

Comment 14 errata-xmlrpc 2018-11-06 15:30:49 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7.5 Extended Update Support

Via RHSA-2018:3459 https://access.redhat.com/errata/RHSA-2018:3459

Comment 15 errata-xmlrpc 2018-11-13 16:30:36 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise MRG 2

Via RHSA-2018:3586 https://access.redhat.com/errata/RHSA-2018:3586

Comment 16 errata-xmlrpc 2018-11-13 16:32:50 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7.4 Extended Update Support

Via RHSA-2018:3540 https://access.redhat.com/errata/RHSA-2018:3540

Comment 17 errata-xmlrpc 2018-11-13 17:50:12 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7.2 Advanced Update Support
  Red Hat Enterprise Linux 7.2 Update Services for SAP Solutions
  Red Hat Enterprise Linux 7.2 Telco Extended Update Support

Via RHSA-2018:3590 https://access.redhat.com/errata/RHSA-2018:3590

Comment 18 errata-xmlrpc 2018-11-13 17:50:38 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7.3 Extended Update Support

Via RHSA-2018:3591 https://access.redhat.com/errata/RHSA-2018:3591


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