CVE-2026-68290: rds: tcp: unregister sysctl before tearing down listen socket

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

rds: tcp: unregister sysctl before tearing down listen socket

rds_tcp_exit_net() frees the per-netns RDS TCP listen socket via
rds_tcp_kill_sock() before unregistering the per-netns sysctl table.  Since
rds_tcp_skbuf_handler() derives the netns from
rtn->rds_tcp_listen_sock->sk, a concurrent sysctl write can race with
netns teardown and dereference the freed socket/sk.

KASAN reports the race as:

  BUG: KASAN: slab-use-after-free in rds_tcp_skbuf_handler+0x2aa/0x2e0
  rds_tcp_skbuf_handler              net/rds/tcp.c:721
  proc_sys_call_handler              fs/proc/proc_sysctl.c
  vfs_write                          fs/read_write.c
  __x64_sys_pwrite64                 fs/read_write.c

Fix this by unregistering the RDS TCP sysctl table before calling
rds_tcp_kill_sock().  unregister_net_sysctl_table() prevents new sysctl
handlers from starting and waits for in-flight handlers to finish, so
the listen socket can then be released safely. The fix was tested
against the linked reproducer.

The Linux kernel CVE team has assigned CVE-2026-68290 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.12.10 with commit de8d6de0ee27be4b2b1e5b06f04aeacbabbba492 and fixed in 6.12.101 with commit 80fffed08dc1c10e971066941d2daa56253f1552
	Issue introduced in 6.13 with commit 7f5611cbc4871c7fb1ad36c2e5a9edad63dca95c and fixed in 6.18.42 with commit 16df2d154ec82e2f7e7585b4fa154751ba37729a
	Issue introduced in 6.13 with commit 7f5611cbc4871c7fb1ad36c2e5a9edad63dca95c and fixed in 7.1.6 with commit 3aa13fe0c1bb7bc5312f878e61523e5d8cf3f85d
	Issue introduced in 6.13 with commit 7f5611cbc4871c7fb1ad36c2e5a9edad63dca95c and fixed in 7.2-rc5 with commit 167e54c703ccd4fa028feb568b0d1002020cff86

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68290
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/rds/tcp.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/80fffed08dc1c10e971066941d2daa56253f1552
	https://git.kernel.org/stable/c/16df2d154ec82e2f7e7585b4fa154751ba37729a
	https://git.kernel.org/stable/c/3aa13fe0c1bb7bc5312f878e61523e5d8cf3f85d
	https://git.kernel.org/stable/c/167e54c703ccd4fa028feb568b0d1002020cff86