linux-cve-announce - CVE-2025-38067: rseq: Fix segfault on registration when rseq

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Message-ID: <2025061837-CVE-2025-38067-b173@gregkh>
Date: Wed, 18 Jun 2025 11:34:02 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38067: rseq: Fix segfault on registration when rseq_cs is non-zero

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

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

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

rseq: Fix segfault on registration when rseq_cs is non-zero

The rseq_cs field is documented as being set to 0 by user-space prior to
registration, however this is not currently enforced by the kernel. This
can result in a segfault on return to user-space if the value stored in
the rseq_cs field doesn't point to a valid struct rseq_cs.

The correct solution to this would be to fail the rseq registration when
the rseq_cs field is non-zero. However, some older versions of glibc
will reuse the rseq area of previous threads without clearing the
rseq_cs field and will also terminate the process if the rseq
registration fails in a secondary thread. This wasn't caught in testing
because in this case the leftover rseq_cs does point to a valid struct
rseq_cs.

What we can do is clear the rseq_cs field on registration when it's
non-zero which will prevent segfaults on registration and won't break
the glibc versions that reuse rseq areas on thread creation.

The Linux kernel CVE team has assigned CVE-2025-38067 to this issue.

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

	Fixed in 6.14.9 with commit 2df285dab00fa03a3ef939b6cb0d0d0aeb0791db
	Fixed in 6.15 with commit fd881d0a085fc54354414aed990ccf05f282ba53

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-2025-38067
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:
	kernel/rseq.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/2df285dab00fa03a3ef939b6cb0d0d0aeb0791db
	https://git.kernel.org/stable/c/fd881d0a085fc54354414aed990ccf05f282ba53