5.5

CVE-2024-35846

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

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
Daten sind bereitgestellt durch National Vulnerability Database (NVD)
Linux ≫ Linux Kernel Version >= 6.8 < 6.8.9
Linux ≫ Linux Kernel Version6.9 Updaterc1
Linux ≫ Linux Kernel Version6.9 Updaterc2
Linux ≫ Linux Kernel Version6.9 Updaterc3
Linux ≫ Linux Kernel Version6.9 Updaterc4
Linux ≫ Linux Kernel Version6.9 Updaterc5
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EPSS Metriken
Typ Quelle Score Percentile
EPSS FIRST.org 0.19% 0.087
CVSS Metriken
Quelle Base Score Exploit Score Impact Score Vector String
nvd@nist.gov 5.5 1.8 3.6
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE-476 NULL Pointer Dereference

The product dereferences a pointer that it expects to be valid but is NULL.

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