CVE-2026-89549: sunrpc: route to a populated pool in svc_pool_for_cpu()

CVE-2026-89549: sunrpc: route to a populated pool in svc_pool_for_cpu()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

sunrpc: route to a populated pool in svc_pool_for_cpu()

svc_set_num_threads() spreads the requested threads evenly across the
service's pools (base = nrservs / sv_nrpools).  When a service runs
fewer threads than it has pools -- e.g. an nfsd configured with fewer
threads than the host has NUMA nodes while running in "pernode" or
"percpu" mode -- the trailing pools are left with no threads at all.

svc_xprt_enqueue() selects a pool from the CPU servicing the transport,
queues the transport on that pool's sp_xprts, and only wakes a thread
from the same pool.  Each thread services exclusively its own pool, so a
transport that lands on a threadless pool is enqueued on sp_xprts and
never picked up: the connection hangs indefinitely.

Have svc_pool_for_cpu() skip pools that currently have no threads,
falling back to the next populated pool.  This trades NUMA locality for
a guarantee that the work is actually serviced.  sp_nrthreads is only
updated under the service mutex; the lockless read here is a best-effort
routing hint, so annotate it with data_race().

The Linux kernel CVE team has assigned CVE-2026-89549 to this issue.


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

	Issue introduced in 2.6.19 with commit bfd241600a3b0db4fe43c859f1460d0a958d924a and fixed in 6.12.109 with commit 011479cf9a7657d4a3e7cc42a784ac63df594170
	Issue introduced in 2.6.19 with commit bfd241600a3b0db4fe43c859f1460d0a958d924a and fixed in 6.18.50 with commit 9d04d64ad192439835ed9884d767353061c3ed6f
	Issue introduced in 2.6.19 with commit bfd241600a3b0db4fe43c859f1460d0a958d924a and fixed in 7.2.4 with commit 8f766d2d0b4dabf54f8b35812df2b4f481d13316
	Issue introduced in 2.6.19 with commit bfd241600a3b0db4fe43c859f1460d0a958d924a and fixed in 7.3-rc1 with commit f6310491c4cdb88af73aa551ec9df1f10a90c709

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-2026-89549
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/sunrpc/svc.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/011479cf9a7657d4a3e7cc42a784ac63df594170
	https://git.kernel.org/stable/c/9d04d64ad192439835ed9884d767353061c3ed6f
	https://git.kernel.org/stable/c/8f766d2d0b4dabf54f8b35812df2b4f481d13316
	https://git.kernel.org/stable/c/f6310491c4cdb88af73aa551ec9df1f10a90c709