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
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