linux-cve-announce - CVE-2025-21629: net: reenable NETIF_F_IPV6

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Message-ID: <2025011517-CVE-2025-21629-e230@gregkh>
Date: Wed, 15 Jan 2025 14:06:27 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21629: net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets

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

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

net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets

The blamed commit disabled hardware offoad of IPv6 packets with
extension headers on devices that advertise NETIF_F_IPV6_CSUM,
based on the definition of that feature in skbuff.h:

 *   * - %NETIF_F_IPV6_CSUM
 *     - Driver (device) is only able to checksum plain
 *       TCP or UDP packets over IPv6. These are specifically
 *       unencapsulated packets of the form IPv6|TCP or
 *       IPv6|UDP where the Next Header field in the IPv6
 *       header is either TCP or UDP. IPv6 extension headers
 *       are not supported with this feature. This feature
 *       cannot be set in features for a device with
 *       NETIF_F_HW_CSUM also set. This feature is being
 *       DEPRECATED (see below).

The change causes skb_warn_bad_offload to fire for BIG TCP
packets.

[  496.310233] WARNING: CPU: 13 PID: 23472 at net/core/dev.c:3129 skb_warn_bad_offload+0xc4/0xe0

[  496.310297]  ? skb_warn_bad_offload+0xc4/0xe0
[  496.310300]  skb_checksum_help+0x129/0x1f0
[  496.310303]  skb_csum_hwoffload_help+0x150/0x1b0
[  496.310306]  validate_xmit_skb+0x159/0x270
[  496.310309]  validate_xmit_skb_list+0x41/0x70
[  496.310312]  sch_direct_xmit+0x5c/0x250
[  496.310317]  __qdisc_run+0x388/0x620

BIG TCP introduced an IPV6_TLV_JUMBO IPv6 extension header to
communicate packet length, as this is an IPv6 jumbogram. But, the
feature is only enabled on devices that support BIG TCP TSO. The
header is only present for PF_PACKET taps like tcpdump, and not
transmitted by physical devices.

For this specific case of extension headers that are not
transmitted, return to the situation before the blamed commit
and support hardware offload.

ipv6_has_hopopt_jumbo() tests not only whether this header is present,
but also that it is the only extension header before a terminal (L4)
header.

The Linux kernel CVE team has assigned CVE-2025-21629 to this issue.

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

	Issue introduced in 6.1.116 with commit a84978a9cda68f0afe3f01d476c68db21526baf1 and fixed in 6.1.124 with commit ac9cfef69565021c9e1022a493a9c40b03e2caf9
	Issue introduced in 6.6.60 with commit c69bc67c1cb211aa390bea6e512bb01b1241fefb and fixed in 6.6.70 with commit 95ccf006bbc8b59044313b8c309dcf29c546abd4
	Issue introduced in 6.12 with commit 04c20a9356f283da623903e81e7c6d5df7e4dc3c and fixed in 6.12.9 with commit d3b7a9c7597b779039a51d7b34116fbe424bf2b7
	Issue introduced in 6.12 with commit 04c20a9356f283da623903e81e7c6d5df7e4dc3c and fixed in 6.13-rc6 with commit 68e068cabd2c6c533ef934c2e5151609cf6ecc6d
	Issue introduced in 4.19.323 with commit bcefc3cd7f592a70fcbbbfd7ad1fbc69172ea78b
	Issue introduced in 5.4.285 with commit 477b35d94a21530046fe91589960732fcf2b29ed
	Issue introduced in 5.10.229 with commit a27a5c40ee4cbe00294e2c76160de5f2589061ba
	Issue introduced in 5.15.171 with commit 9f605135a5c0fe614c2b15197b9ced1e217eca59
	Issue introduced in 6.11.7 with commit 705350fbd6ed4b5d89ee045fa57a0594a72b17d7

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-2025-21629
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/core/dev.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/ac9cfef69565021c9e1022a493a9c40b03e2caf9
	https://git.kernel.org/stable/c/95ccf006bbc8b59044313b8c309dcf29c546abd4
	https://git.kernel.org/stable/c/d3b7a9c7597b779039a51d7b34116fbe424bf2b7
	https://git.kernel.org/stable/c/68e068cabd2c6c533ef934c2e5151609cf6ecc6d