CVE-2026-74709: xsk: clear metadata pointer when no timestamp is requested

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

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

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

xsk: clear metadata pointer when no timestamp is requested

User space can change metadata flags after request processing. Rereading
them during completion can therefore make the kernel write a timestamp
that was not requested when the packet was submitted.

Clear the metadata pointer during request processing unless timestamp
completion is requested. Completion handling can then use the pointer
itself instead of rereading the flags.

On the mlx5 multi-packet WQE path metadata is evaluated per batch:
xsk_tx_metadata_request() runs only for the descriptor that starts a
session, just like the checksum offload that is applied once through the
shared WQE. Only that descriptor's pointer is reset, so completion
handling can record a timestamp for the other descriptors of the session
regardless of their own XDP_TXMD_FLAGS_TIMESTAMP bit. The write stays
inside the metadata area; the single-WQE, other zero-copy, and generic
paths reset the pointer per descriptor and are unaffected.

The Linux kernel CVE team has assigned CVE-2026-74709 to this issue.


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

	Issue introduced in 6.15 with commit ca4419f15abd19ba8be1e109661b60f9f5b6c9f0 and fixed in 6.18.45 with commit 0ba2e1eb07a826d021344e2f146b6716c58139eb
	Issue introduced in 6.15 with commit ca4419f15abd19ba8be1e109661b60f9f5b6c9f0 and fixed in 7.1.9 with commit eb4c613d4ebc3f664e70d572b8867ba114a8754e
	Issue introduced in 6.15 with commit ca4419f15abd19ba8be1e109661b60f9f5b6c9f0 and fixed in 7.2 with commit 9f60a67df8d3c862503bee62bada8e7089cba438
	Issue introduced in 6.14.2 with commit d9d736c416c9a85f84e15435ba82a177262e745b

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-2026-74709
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:
	include/net/xdp_sock.h
	net/xdp/xsk.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/0ba2e1eb07a826d021344e2f146b6716c58139eb
	https://git.kernel.org/stable/c/eb4c613d4ebc3f664e70d572b8867ba114a8754e
	https://git.kernel.org/stable/c/9f60a67df8d3c862503bee62bada8e7089cba438