CVE-2026-74436: rxrpc: serialize kernel accept preallocation with socket teardown

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

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

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

rxrpc: serialize kernel accept preallocation with socket teardown

rxrpc_kernel_charge_accept() reads rx->backlog without any
socket/backlog synchronization and passes that raw pointer into
rxrpc_service_prealloc_one(). A concurrent rxrpc_discard_prealloc()
sets rx->backlog = NULL and frees the backlog rings, so a kernel
preallocation worker can keep using a freed struct rxrpc_backlog
while updating *_backlog_head/tail and array slots.

Serialize the state check and backlog lookup with the socket lock,
and reject kernel preallocation once teardown has disabled
listening or discarded the service backlog.

The Linux kernel CVE team has assigned CVE-2026-74436 to this issue.


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

	Issue introduced in 4.9 with commit 00e907127e6f86d0f9b122d9b4347a8aa09a8b61 and fixed in 6.6.148 with commit 0337cdba0c477f176c0459bed012109453184573
	Issue introduced in 4.9 with commit 00e907127e6f86d0f9b122d9b4347a8aa09a8b61 and fixed in 6.12.101 with commit dfa0b2bbc5e50119f89c6b5407faa5ed86dfa7c5
	Issue introduced in 4.9 with commit 00e907127e6f86d0f9b122d9b4347a8aa09a8b61 and fixed in 6.18.40 with commit 35a967ff8b24db09ee429c39c5b5e6571639997d
	Issue introduced in 4.9 with commit 00e907127e6f86d0f9b122d9b4347a8aa09a8b61 and fixed in 7.1.5 with commit 1741378a7a83dfd8e53a9196730df709b903cd33
	Issue introduced in 4.9 with commit 00e907127e6f86d0f9b122d9b4347a8aa09a8b61 and fixed in 7.2-rc1 with commit dc175389b18c29a5303ee83169ec653adfae3e17

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-2026-74436
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/rxrpc/call_accept.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/0337cdba0c477f176c0459bed012109453184573
	https://git.kernel.org/stable/c/dfa0b2bbc5e50119f89c6b5407faa5ed86dfa7c5
	https://git.kernel.org/stable/c/35a967ff8b24db09ee429c39c5b5e6571639997d
	https://git.kernel.org/stable/c/1741378a7a83dfd8e53a9196730df709b903cd33
	https://git.kernel.org/stable/c/dc175389b18c29a5303ee83169ec653adfae3e17