CVE-2026-99192: net: bcmgenet: unshare the skb before writing the control block

CVE-2026-99192: net: bcmgenet: unshare the skb before writing the control block

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

net: bcmgenet: unshare the skb before writing the control block

bcmgenet stores first_cb, last_cb and bytes_sent in the skb control
block and reads them back on completion to free the skb and credit BQL.
ether_setup() leaves IFF_TX_SKB_SHARING set, so the stack can resubmit
a shared skb that is still in the ring. The next transmit overwrites
last_cb, so the earlier slots complete without crediting their bytes
and BQL stalls the queue until the watchdog resets it.

Unshare the skb before writing the control block.

Reproduce with pktgen in clone_skb mode, which hands the driver the same
skb while earlier copies are still in the ring:

  modprobe pktgen
  pg=/proc/net/pktgen
  echo "add_device eth0" > $pg/kpktgend_0
  echo "dst_mac AA:BB:CC:DD:EE:FF" > $pg/eth0
  echo "dst 192.0.2.1" > $pg/eth0
  echo "clone_skb 8" > $pg/eth0
  echo "count 0" > $pg/eth0
  echo start > $pg/pgctrl &
  sleep 5
  echo stop > $pg/pgctrl
  wait
  cat /sys/class/net/eth0/queues/tx-0/byte_queue_limits/inflight

inflight stays nonzero on the now idle queue. clone_skb 0 leaves it at
zero.

The Linux kernel CVE team has assigned CVE-2026-99192 to this issue.


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

	Issue introduced in 4.13 with commit f48bed16a756f5bc0244acd581f61968f7d7c2a4 and fixed in 6.18.59 with commit 40c04abcbc34e3afe338f41dae851ecbd72852ac
	Issue introduced in 4.13 with commit f48bed16a756f5bc0244acd581f61968f7d7c2a4 and fixed in 7.2.13 with commit 7939ad3b4db9eadf45a64f0524f38337a9494672
	Issue introduced in 4.13 with commit f48bed16a756f5bc0244acd581f61968f7d7c2a4 and fixed in 7.3 with commit 89771ce4f8f67dcffae561b2ccac95c0f6e3aa01
	Issue introduced in 3.16.50 with commit fb4ca2b4bc6712a6ad635df5b9b41131846589f9

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-2026-99192
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/broadcom/genet/bcmgenet.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/40c04abcbc34e3afe338f41dae851ecbd72852ac
	https://git.kernel.org/stable/c/7939ad3b4db9eadf45a64f0524f38337a9494672
	https://git.kernel.org/stable/c/89771ce4f8f67dcffae561b2ccac95c0f6e3aa01