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.
Haven't tried, should be 100%.
Steps to Reproduce:
I can prepare a malicious frontend if necessary.
Created attachment 302934 [details]
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.
This issue is enhanced by the CVE-2008-1952 (another size limit check added).
Public paper about exploitation of this flaw:
This was addressed via:
Red Hat Enterprise Linux version 5 (RHSA-2008:0194)
RHEL Virtualization version 5 (RHSA-2008:0194)