Google: sys-kernel/cchost-kernel-6_12, sys-kernel/cchost-kernel-6_18, sys-kernel/csql-kernel-6_12, sys-kernel/csql-kernel-6_18, sys-kernel/lakitu-kernel-6_12, sys-kernel/lakitu-kernel-6_18, sys-kernel/lakitu-nc-kernel-6_12, sys-kernel/lakitu-nc-kernel-6_18: security update to 19999.44.106

medium Tenable Cloud Security Plugin ID 475440

Description

There are packages installed that are affected by a vulnerability referenced in the following CVE:

- In the Linux kernel, the following vulnerability has been resolved: memcg: bypass the reclaim and oom
killer for dying tasks once oom_reaper is done At Meta, we are seeing instances where an OOM killed job is
stuck in the exit path for several hours. In one particular case, the job was stuck for more than 8 hours
and I had to manually remove the memory.max limits to allow the process to exit. The job was a single
process job and had ~55 GiB memory.max and zswap enabled. It had almost 0 anon in memory and ~111 GiB in
zswap compressed to ~51 GiB zswap pool (i.e. almost all of memory.current was zswap). Nothing was left on
the LRUs to reclaim. On further inspection, I observed ~20k threads of that process stuck with the
following stack: [<0>] mem_cgroup_out_of_memory+0x4e/0xa0 [<0>] charge_memcg+0x8bf/0x990 [<0>]
mem_cgroup_swapin_charge_folio+0x4e/0x80 [<0>] __read_swap_cache_async+0x10c/0x260 [<0>]
swapin_readahead+0x116/0x3f0 [<0>] do_swap_page+0x13c/0x1ce0 [<0>] handle_mm_fault+0x61d/0x11f0 [<0>]
do_user_addr_fault+0x3e7/0x6d0 [<0>] exc_page_fault+0x8f/0x110 [<0>] asm_exc_page_fault+0x22/0x30 [<0>]
__get_user_8+0x14/0x20 [<0>] futex_cleanup+0x27/0x1c0 [<0>] futex_exit_release+0x47/0x60 [<0>]
do_exit+0x107/0x940 [<0>] do_group_exit+0x81/0xa0 [<0>] get_signal+0x2b1/0x6e0 [<0>]
arch_do_signal_or_restart+0x1a/0x1c0 [<0>] exit_to_user_mode_loop+0xa8/0x1c0 [<0>]
do_syscall_64+0x152/0x250 [<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53 In addition the dmesg was filled
with "Out of memory and no killable processes..." messages. I have no idea why oom reaper was not able to
reap/unmap the process. My guess is that since oom reaper tries to acquire mmap_lock in read mode limited
number of times and then gives up, there might be a thread of that process which had mmap_lock in write
mode at that time. My initial suspicion was the futex_cleanup and kernel page fault causing infinite fault
and charge retries but that was put to rest in previous discussions happened on similar problem [1]. My
current theory is that it is just a simple slow serialization behind the oom_lock. Unlike page allocator,
memcg charge code takes the oom_lock without the "try". Though memcg oom code uses mutex_lock_killable(),
note that in the call stack get_signal() consumes SIGKILL (or sigdelset(SIGKILL)) before calling
do_group_exit(). So this mutex_lock_killable() is just a mutex_lock() here. Therefore 10s of thousands of
threads are waiting on oom_lock and one by one they get -EFAULT from get_user() in the futex cleanup code
and bails out. Discussion from [1] led to commit a75ffa26122b ("memcg, oom: do not bypass oom killer for
dying tasks") which routes dying tasks into the OOM path precisely so the oom_reaper can reap their mm and
free the memory asynchronously. But the reaper is best-effort and one-shot: if it cannot take mmap_lock
for read (e.g. a sibling thread holds it for write) it sets MMF_OOM_SKIP and never retries, leaving only
the glacial oom_lock-serialized synchronous drain. Once MMF_OOM_SKIP is set there is no more asynchronous
reclaim coming for the mm, so a dying task charging against it has nothing left to wait for: it frees its
memory only once it finishes exiting. Running reclaim and the (no-victim) OOM killer for it is then
pointless, and doing it for 10s of thousands of exiting threads is what serializes them behind oom_lock.
So before reclaim, if current is an OOM victim whose reaper is done, fail the charge. Reproduced with 20k
threads, each parking a robust futex head on its own zswapped page, OOM-group-killed while a sibling holds
mmap_lock for write so the reaper gives up and sets MMF_OOM_SKIP. Tested on next-20260728 and baseline
show ~90 seconds exit time while with the patch the exit time reduced to ~3 seconds. (CVE-2026-93241)

Solution

Update the sys-kernel/cchost-kernel-6_12 library and its related packages to version 19999.44.106 or later.

Plugin Details

Severity: Medium

ID: 475440

Version: Revision 1.1

Type: Local

Family: Google COS Security Checks

Published: 10/16/2026

Updated: 10/16/2026

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.61

Vendor

Vendor Severity: LOW

CVSS v2

Risk Factor: Low

Base Score: 1.9

Temporal Score: 1.4

Vector: CVSS2#AV:L/AC:M/Au:N/C:N/I:N/A:P

CVSS Score Source: CVE-2026-93241

CVSS v3

Risk Factor: Medium

Base Score: 5.5

Temporal Score: 4.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 9/24/2026

Reference Information

CVE: CVE-2026-93241

Detections

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