CVE-2026-74668: packet: use consistent hard_header_len in TX_RING send path

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

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

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

packet: use consistent hard_header_len in TX_RING send path

tpacket_snd() reads dev->hard_header_len independently for skb
allocation and header construction in tpacket_fill_skb(). Concurrent
netdevice reconfiguration can therefore make the reserved headroom
smaller than the amount later pushed, or make copylen - hard_header_len
negative.

Snapshot hard_header_len once before processing ring frames and use it
for the frame limit, headroom allocation, copy length, and skb
construction. Pass the snapshot to tpacket_fill_skb().

The separate SOCK_DGRAM consistency problem between hard_header_len and
header_ops->create is not addressed here.

The Linux kernel CVE team has assigned CVE-2026-74668 to this issue.


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

	Issue introduced in 2.6.31 with commit 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 and fixed in 6.6.152 with commit d85d2fd54e901637c81d847811e03c662aee13cd
	Issue introduced in 2.6.31 with commit 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 and fixed in 6.12.104 with commit 016763e829cac37b3234eace86fd0a4c560de4a7
	Issue introduced in 2.6.31 with commit 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 and fixed in 6.18.45 with commit 27e068d1b35dbec10a3cf268887c94407be4badc
	Issue introduced in 2.6.31 with commit 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 and fixed in 7.1.9 with commit d48ea5c9c4c34dc0df621f0e39ed3a16b644621a
	Issue introduced in 2.6.31 with commit 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 and fixed in 7.2 with commit 21b5953e7494c16a42e6cd8cf110e18d13ae4a6b

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-2026-74668
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/packet/af_packet.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/d85d2fd54e901637c81d847811e03c662aee13cd
	https://git.kernel.org/stable/c/016763e829cac37b3234eace86fd0a4c560de4a7
	https://git.kernel.org/stable/c/27e068d1b35dbec10a3cf268887c94407be4badc
	https://git.kernel.org/stable/c/d48ea5c9c4c34dc0df621f0e39ed3a16b644621a
	https://git.kernel.org/stable/c/21b5953e7494c16a42e6cd8cf110e18d13ae4a6b