Bug 1224595 (CVE-2024-35846)

Summary: VUL-0: CVE-2024-35846: kernel: mm: zswap: fix shrinker NULL crash with cgroup_disable=memory
Product: [Novell Products] SUSE Security Incidents Reporter: SMASH SMASH <smash_bz>
Component: IncidentsAssignee: Security Team bot <security-team>
Status: RESOLVED INVALID QA Contact: Security Team bot <security-team>
Severity: Normal    
Priority: P3 - Medium CC: gabriele.sonnu, jlee, mkoutny
Version: unspecified   
Target Milestone: ---   
Hardware: Other   
OS: Other   
URL: https://smash.suse.de/issue/406451/
Whiteboard: CVSSv3.1:SUSE:CVE-2024-35846:5.5:(AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Found By: Security Response Team Services Priority:
Business Priority: Blocker: ---
Marketing QA Status: --- IT Deployment: ---

Description SMASH SMASH 2024-05-20 15:29:55 UTC 
In the Linux kernel, the following vulnerability has been resolved:

mm: zswap: fix shrinker NULL crash with cgroup_disable=memory

Christian reports a NULL deref in zswap that he bisected down to the zswap
shrinker.  The issue also cropped up in the bug trackers of libguestfs [1]
and the Red Hat bugzilla [2].

The problem is that when memcg is disabled with the boot time flag, the
zswap shrinker might get called with sc->memcg == NULL.  This is okay in
many places, like the lruvec operations.  But it crashes in
memcg_page_state() - which is only used due to the non-node accounting of
cgroup's the zswap memory to begin with.

Nhat spotted that the memcg can be NULL in the memcg-disabled case, and I
was then able to reproduce the crash locally as well.

[1] https://github.com/libguestfs/libguestfs/issues/139
[2] https://bugzilla.redhat.com/show_bug.cgi?id=2275252

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2024-35846
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2024/CVE-2024-35846.mbox
https://git.kernel.org/stable/c/b0fdabc908a7f81d12382c87ca9e46a9c2e14042
https://git.kernel.org/stable/c/682886ec69d22363819a83ddddd5d66cb5c791e1
https://www.cve.org/CVERecord?id=CVE-2024-35846
https://bugzilla.redhat.com/show_bug.cgi?id=2281270
Comment 1 Joey Lee 2024-05-21 08:50:13 UTC 
https://www.suse.com/security/cve/CVE-2024-35846.html
cvss 5.5
Comment 3 Gabriele Sonnu 2024-06-10 12:28:04 UTC 
All done, closing.