CVE-2026-80889: can: isotp: fix timer drain order, wakeup handling and tx_gen ordering

CVE-2026-80889: can: isotp: fix timer drain order, wakeup handling and tx_gen ordering

[Greg Kroah-Hartman]

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

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

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

can: isotp: fix timer drain order, wakeup handling and tx_gen ordering

This patch is a follow-up to commit cf070fe33bfb ("can: isotp: serialize
TX state transitions under so->rx_lock") which addresses following
sashiko-bot findings:

- isotp_sendmsg(): drain so->txfrtimer first so a stale callback can't
  re-arm echotimer after the claim

- isotp_release(): wake so->wait after forcing ISOTP_SHUTDOWN so a
  sleeping sendmsg() claim isn't stranded

- isotp_sendmsg(): have both wait_event_interruptible() calls in
  isotp_sendmsg() also wake on ISOTP_SHUTDOWN and do not return claim to
  IDLE to avoid corrupting a concurrent isotp_release() process.

- isotp_sendmsg(): handle potential claim of a new transfer when
  the wait_event_interruptible() call returns in CAN_ISOTP_WAIT_TX_DONE
  mode. Don't touch timers and states of the new transfer if a new thread
  incremented so->tx_gen before getting the lock at err_event_drop.

- isotp_sendmsg(): handle a stuck can_send() and omit timer and state
  changes if a new transfer was claimed. wait_tx_done() returns the error
  recorded in so->tx_result[], tagged with the caller's own generation.

- isotp_tx_timeout(): on a claimed timeout, record the ECOMM error for
  the timed-out transfer's own generation in so->tx_result[]; sk->sk_err
  is raised unconditionally, same as every other error path here.

- isotp_tx_gen_done()/isotp_tx_timeout(): always read tx.state (acquire)
  before tx_gen - the reverse order let a weakly ordered CPU pair a fresh
  tx.state with a stale tx_gen/tx_result slot.

- isotp_sendmsg(): wait_tx_done: drain sk_err via sock_error() once we
  have read the result from so->tx_result[], so an already-reported error
  doesn't stay latched for a later poll()/SO_ERROR.

Also align the remaining lock-free so->tx.state/rx.state/cfecho accesses
and use skb->hash as unique loopback echo frame indicator.

The Linux kernel CVE team has assigned CVE-2026-80889 to this issue.


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

	Issue introduced in 5.10.265 with commit bbedeb67a9a684f2fb78c55bd3662c400526715e and fixed in 5.10.267 with commit 8acab9fc66d6f426c36968c91a979f70784945a7
	Issue introduced in 5.15.216 with commit 377a8f500704da42ed86a4541ed930e9dcfdb2ea and fixed in 5.15.218 with commit af7e25c649ed68cbad07f8185af0f31b892cbf29
	Issue introduced in 6.1.183 with commit 6da8119e8dd542194103139812d1a4b7dcd1aedd and fixed in 6.1.185 with commit 2753722612d8824d3910096f93059f669009b0f0
	Issue introduced in 6.6.148 with commit 0b05eca9589f609e2491b528dccf683168a4cda8 and fixed in 6.6.151 with commit bf5c4a8b24acb12739ebb9aea5510b007e4f5239
	Issue introduced in 6.12.101 with commit a7d90e7b5e75d7406c889fe36e9a61ee364a00cb and fixed in 6.12.103 with commit deca7746b57d982cd4f0301f4443f56780c4a048
	Issue introduced in 6.18.40 with commit 37beb16e08cae94cc05840c7274225e3b0b38ae7 and fixed in 6.18.44 with commit 10be509fa8fd95d1e47d40d1f68b0b26dfe9d572
	Issue introduced in 7.1.5 with commit 4f1fdf1a1c317bcac0c6b6c8e12642c9983de1ca and fixed in 7.1.8 with commit 35c62ac98d06669aa3f0f38b7829eaca929a611e

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-2026-80889
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/can/isotp.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/8acab9fc66d6f426c36968c91a979f70784945a7
	https://git.kernel.org/stable/c/af7e25c649ed68cbad07f8185af0f31b892cbf29
	https://git.kernel.org/stable/c/2753722612d8824d3910096f93059f669009b0f0
	https://git.kernel.org/stable/c/bf5c4a8b24acb12739ebb9aea5510b007e4f5239
	https://git.kernel.org/stable/c/deca7746b57d982cd4f0301f4443f56780c4a048
	https://git.kernel.org/stable/c/10be509fa8fd95d1e47d40d1f68b0b26dfe9d572
	https://git.kernel.org/stable/c/35c62ac98d06669aa3f0f38b7829eaca929a611e
	https://git.kernel.org/stable/c/050f010f920da17c1044a4f174766ad553e770b6