Bug 679262 - [RFE] kernel: kptr_restrict for hiding kernel pointers from unprivileged users [rhel-6.2]
[RFE] kernel: kptr_restrict for hiding kernel pointers from unprivileged user...
Status: CLOSED ERRATA
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: kernel (Show other bugs)
6.2
Unspecified Unspecified
high Severity high
: rc
: ---
Assigned To: Phillip Lougher
Boris Ranto
: FutureFeature
Depends On: 679261 679263
Blocks: 1300182
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Reported: 2011-02-21 23:40 EST by Eugene Teo (Security Response)
Modified: 2016-01-20 03:09 EST (History)
12 users (show)

See Also:
Fixed In Version: kernel-2.6.32-150.el6
Doc Type: Enhancement
Doc Text:
In Red Hat Enterprise Linux 6.2, due to security concerns, addresses in /proc/kallsyms and /proc/modules show all zeros when accessed by a non-root user.
Story Points: ---
Clone Of: 679261
Environment:
Last Closed: 2011-12-06 07:43:58 EST
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
CRM:
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---


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Description Eugene Teo (Security Response) 2011-02-21 23:40:52 EST
+++ This bug was initially created as a clone of Bug #679261 +++

Description of problem:
Add the %pK printk format specifier and the /proc/sys/kernel/kptr_restrict sysctl.
    
The %pK format specifier is designed to hide exposed kernel pointers, specifically via /proc interfaces.  Exposing these pointers provides an easy target for kernel write vulnerabilities, since they reveal the locations of writable structures containing easily triggerable function pointers.  The behavior of %pK depends on the kptr_restrict sysctl.
    
If kptr_restrict is set to 0, no deviation from the standard %p behavior occurs.  If kptr_restrict is set to 1, the default, if the current user (intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG (currently in the LSM tree), kernel pointers using %pK are printed as 0's. If kptr_restrict is set to 2, kernel pointers using %pK are printed as 0's regardless of privileges.  Replacing with 0's was chosen over the default "(null)", which cannot be parsed by userland %p, which expects "(nil)".

Upstream commit:
http://git.kernel.org/linus/455cd5ab305c90ffc422dd2e0fb634730942b257

Also backport:
drm: do not leak kernel addresses via /proc/dri/*/vma
http://git.kernel.org/linus/01e2f533a234dc62d16c0d3d4fb9d71cf1ce50c3

timer debug: Hide kernel addresses via %pK in /proc/timer_list
http://git.kernel.org/linus/f590308536db432e4747f562b29e5858123938e9

[PATCH v2] use %pK for /proc/kallsyms and /proc/modules
http://marc.info/?l=linux-kernel&m=129608894604282&w=2 (not upstream yet)
Comment 1 Phillip Lougher 2011-04-04 13:23:18 EDT
(In reply to comment #0)

> [PATCH v2] use %pK for /proc/kallsyms and /proc/modules
> http://marc.info/?l=linux-kernel&m=129608894604282&w=2 (not upstream yet)

Now in mainline

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=9f36e2c448007b54851e7e4fa48da97d1477a175
Comment 2 Phillip Lougher 2011-04-12 11:25:48 EDT
(In reply to comment #0)

> If kptr_restrict is set to 0, no deviation from the standard %p behavior
> occurs.  If kptr_restrict is set to 1, the default, if the current user
> (intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG
> (currently in the LSM tree), kernel pointers using %pK are printed as 0's.
>
> Upstream commit:
> http://git.kernel.org/linus/455cd5ab305c90ffc422dd2e0fb634730942b257
>

This patch requires the CAP_SYSLOG capability, added by mainline commit

http://git.kernel.org/linus/ce6ada35bdf710d16582cc4869c26722547e6f11 

options?

1. Replace CAP_SYSLOG with CAP_SYS_ADMIN
2. Add CAP_SYSLOG patch
3. reject BZ
Comment 3 Eugene Teo (Security Response) 2011-04-12 22:07:53 EDT
(In reply to comment #2)
> (In reply to comment #0)
> 
> > If kptr_restrict is set to 0, no deviation from the standard %p behavior
> > occurs.  If kptr_restrict is set to 1, the default, if the current user
> > (intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG
> > (currently in the LSM tree), kernel pointers using %pK are printed as 0's.
> >
> > Upstream commit:
> > http://git.kernel.org/linus/455cd5ab305c90ffc422dd2e0fb634730942b257
> >
> 
> This patch requires the CAP_SYSLOG capability, added by mainline commit
> 
> http://git.kernel.org/linus/ce6ada35bdf710d16582cc4869c26722547e6f11 
> 
> options?
> 
> 1. Replace CAP_SYSLOG with CAP_SYS_ADMIN
> 2. Add CAP_SYSLOG patch
> 3. reject BZ

Perhaps take option 1, and then mention about the CAP_SYSLOG patch in your patch submission for discussion.
Comment 4 Aristeu Rozanski 2011-05-18 16:07:57 EDT
Patch(es) available on kernel-2.6.32-150.el6
Comment 15 Martin Prpič 2011-11-22 04:57:56 EST
    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
In Red Hat Enterprise Linux 6.2, due to security concerns, addresses in /proc/kallsyms and /proc/modules show all zeros when accessed by a non-root user.
Comment 16 errata-xmlrpc 2011-12-06 07:43:58 EST
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2011-1530.html

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