CVE-2024-35846

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 cgroups 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

Affected Software

References

• https://git.kernel.org/stable/c/682886ec69d22363819a83ddddd5d66cb5c791e1
• https://git.kernel.org/stable/c/b0fdabc908a7f81d12382c87ca9e46a9c2e14042