Bug 443078 (CVE-2008-1943)

Summary: CVE-2008-1943 PVFB backend fails to validate frontend's framebuffer description
Product: [Other] Security Response Reporter: Markus Armbruster <armbru>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact: Martin Jenner <mjenner>
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: bburns, benl, berrange, mgahagan, security-response-team, xen-maint
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2010-12-23 17:46:21 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 443376, 443377, 443585    
Bug Blocks:    
Attachments:
Description Flags
Proposed fix none

Description Markus Armbruster 2008-04-18 15:12:17 UTC 
Description of problem:
The PVFB backend is a user space program running as root in dom0.  A buggy or
malicious frontend can describe its shared framebuffer to it in a way that makes
it map an arbitrary amount of guest memory, malloc an arbitrarily large internal
buffer, or copy arbitrary memory to that buffer.  A domU running a malicious
frontend can abuse the former two for a denial of service attack against dom0. 
It can abuse all three to terminate or crash the backend.  If there's anything
in the backend's address space that gets tickled the wrong way by being read,
the last one is more serious, but I'm not aware of anything like that.

Version-Release number of selected component (if applicable):
I believe all versions are vulnerable to the first two abuses, and all versions
since 3.0.3-45.el5 are additionally vulnerable to the third one.

How reproducible:
Haven't tried, should be 100%.

Steps to Reproduce:
I can prepare a malicious frontend if necessary.
Comment 1 Markus Armbruster 2008-04-18 20:00:21 UTC 
Created attachment 302934 [details]
Proposed fix

The fix makes the backend validate the framebuffer description presented by the
frontend on its shared page on initialization.	Code executing after
initialization is not touched.

All frontends we've shipped so far present the same, fixed set of parameters,
which validates fine.
Comment 6 Jan Lieskovsky 2008-05-21 18:01:52 UTC 
This issue is enhanced by the CVE-2008-1952 (another size limit check added).
Comment 7 Tomas Hoger 2008-10-15 14:39:55 UTC 
Public paper about exploitation of this flaw:

http://marc.info/?l=dailydave&m=122407972124773&w=2
http://invisiblethingslab.com/pub/xenfb-adventures-10.pdf
Comment 8 Vincent Danen 2010-12-23 17:46:21 UTC 
This was addressed via:

Red Hat Enterprise Linux version 5 (RHSA-2008:0194)
RHEL Virtualization version 5 (RHSA-2008:0194)