CVE-2026-74698: net/mlx5e: fix BQL reset on SQ re-activation

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

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

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

net/mlx5e: fix BQL reset on SQ re-activation

mlx5e_queue_start() deactivates and re-activates all channels but closes
only the queue being restarted. mlx5e_activate_txqsq() then
unconditionally calls netdev_tx_reset_queue(), zeroing the BQL counters
of channels that kept their in-flight TX WQEs. The next completion then
over-charges and trips the BUG_ON() in dql_completed():

  kernel BUG at lib/dynamic_queue_limits.c:99!
  RIP: 0010:dql_completed+0x23d/0x280
  Call Trace:
   <IRQ>
   mlx5e_poll_tx_cq+0x668/0xa60
   mlx5e_napi_poll+0x5b/0x7b0
   net_rx_action+0x15a/0x580

Reset BQL only when the SQ has no bytes in flight (sq->cc == sq->pc).

In the case that reset is skipped, the outstanding WQEs will eventually
complete and rebalance the dql. The dql->limit is carried across the
reset.

The Linux kernel CVE team has assigned CVE-2026-74698 to this issue.


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

	Issue introduced in 6.17 with commit b2588ea40ec9472688289c1a644627c0f4a1f33f and fixed in 6.18.45 with commit 88664c48d7d1eca8e1ac92da85c89c26af741cf1
	Issue introduced in 6.17 with commit b2588ea40ec9472688289c1a644627c0f4a1f33f and fixed in 7.1.9 with commit d2897717cd222e575599d903d885c48602699800
	Issue introduced in 6.17 with commit b2588ea40ec9472688289c1a644627c0f4a1f33f and fixed in 7.2 with commit e7386770be1bf810bcd6af39d1e4bfeab3408430

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-2026-74698
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/ethernet/mellanox/mlx5/core/en_main.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/88664c48d7d1eca8e1ac92da85c89c26af741cf1
	https://git.kernel.org/stable/c/d2897717cd222e575599d903d885c48602699800
	https://git.kernel.org/stable/c/e7386770be1bf810bcd6af39d1e4bfeab3408430