linux-cve-announce - CVE-2025-71128: erspan: Initialize options

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Message-ID: <2026011451-CVE-2025-71128-3c25@gregkh>
Date: Wed, 14 Jan 2026 16:07:52 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-71128: erspan: Initialize options_len before referencing options.

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

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

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

erspan: Initialize options_len before referencing options.

The struct ip_tunnel_info has a flexible array member named
options that is protected by a counted_by(options_len)
attribute.

The compiler will use this information to enforce runtime bounds
checking deployed by FORTIFY_SOURCE string helpers.

As laid out in the GCC documentation, the counter must be
initialized before the first reference to the flexible array
member.

After scanning through the files that use struct ip_tunnel_info
and also refer to options or options_len, it appears the normal
case is to use the ip_tunnel_info_opts_set() helper.

Said helper would initialize options_len properly before copying
data into options, however in the GRE ERSPAN code a partial
update is done, preventing the use of the helper function.

Before this change the handling of ERSPAN traffic in GRE tunnels
would cause a kernel panic when the kernel is compiled with
GCC 15+ and having FORTIFY_SOURCE configured:

memcpy: detected buffer overflow: 4 byte write of buffer size 0

Call Trace:
 <IRQ>
 __fortify_panic+0xd/0xf
 erspan_rcv.cold+0x68/0x83
 ? ip_route_input_slow+0x816/0x9d0
 gre_rcv+0x1b2/0x1c0
 gre_rcv+0x8e/0x100
 ? raw_v4_input+0x2a0/0x2b0
 ip_protocol_deliver_rcu+0x1ea/0x210
 ip_local_deliver_finish+0x86/0x110
 ip_local_deliver+0x65/0x110
 ? ip_rcv_finish_core+0xd6/0x360
 ip_rcv+0x186/0x1a0

Reported-at: https://launchpad.net/bugs/2129580

The Linux kernel CVE team has assigned CVE-2025-71128 to this issue.

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

	Issue introduced in 6.15 with commit bb5e62f2d547c4de6d1b144cbce2373a76c33f18 and fixed in 6.18.4 with commit b282b2a9eed848587c1348abdd5d83fa346a2743
	Issue introduced in 6.15 with commit bb5e62f2d547c4de6d1b144cbce2373a76c33f18 and fixed in 6.19-rc4 with commit 35ddf66c65eff93fff91406756ba273600bf61a3

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-2025-71128
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/ipv4/ip_gre.c
	net/ipv6/ip6_gre.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/b282b2a9eed848587c1348abdd5d83fa346a2743
	https://git.kernel.org/stable/c/35ddf66c65eff93fff91406756ba273600bf61a3