CVE-2026-72019: macsec: don't read an unset MAC header in macsec_encrypt()

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

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

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

macsec: don't read an unset MAC header in macsec_encrypt()

macsec_encrypt() reads the Ethernet header via eth_hdr(skb)
(skb->head + skb->mac_header) to memmove() the 12 source/destination MAC
bytes forward and make room for the SecTAG.

On the AF_PACKET SOCK_RAW + PACKET_QDISC_BYPASS transmit path the skb
reaches the macsec ndo_start_xmit() with the MAC header unset, so
eth_hdr(skb) resolves to skb->head + (u16)~0 and the read is out of
bounds: a 12-byte heap over-read that is also emitted on the wire as the
frame's outer source/destination MAC. KASAN reports a slab-out-of-bounds
read in macsec_start_xmit() on 6.0; on current mainline a CONFIG_DEBUG_NET
build flags it as an unset mac header in skb_mac_header().

On the TX path the L2 header is at skb->data, so use skb_eth_hdr(), added
by commit 96cc4b69581d ("macvlan: do not assume mac_header is set in
macvlan_broadcast()") for exactly this purpose.

The Linux kernel CVE team has assigned CVE-2026-72019 to this issue.


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

	Issue introduced in 4.6 with commit c09440f7dcb304002dfced8c0fea289eb25f2da0 and fixed in 6.1.178 with commit dc9ffa1905e72f026d080880a2e4cfc42aa91000
	Issue introduced in 4.6 with commit c09440f7dcb304002dfced8c0fea289eb25f2da0 and fixed in 6.6.145 with commit f21fa533a3ed15ada74106aac4b9ddd078fc6b7a
	Issue introduced in 4.6 with commit c09440f7dcb304002dfced8c0fea289eb25f2da0 and fixed in 6.12.97 with commit e17a42199824973cd8212e95b21ffadf4114a21b
	Issue introduced in 4.6 with commit c09440f7dcb304002dfced8c0fea289eb25f2da0 and fixed in 6.18.40 with commit 2cf10d042562283ff4ae97c02d0993d4f1b5ea29
	Issue introduced in 4.6 with commit c09440f7dcb304002dfced8c0fea289eb25f2da0 and fixed in 7.1.5 with commit c39087ad0b97fc11a3b058dfc8db9fd370762cb9
	Issue introduced in 4.6 with commit c09440f7dcb304002dfced8c0fea289eb25f2da0 and fixed in 7.2-rc3 with commit f5089008f90c0a7c5520dff3934e0af00adf322d

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-2026-72019
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:
	drivers/net/macsec.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/dc9ffa1905e72f026d080880a2e4cfc42aa91000
	https://git.kernel.org/stable/c/f21fa533a3ed15ada74106aac4b9ddd078fc6b7a
	https://git.kernel.org/stable/c/e17a42199824973cd8212e95b21ffadf4114a21b
	https://git.kernel.org/stable/c/2cf10d042562283ff4ae97c02d0993d4f1b5ea29
	https://git.kernel.org/stable/c/c39087ad0b97fc11a3b058dfc8db9fd370762cb9
	https://git.kernel.org/stable/c/f5089008f90c0a7c5520dff3934e0af00adf322d