CVE-2026-80889 can: isotp: fix timer drain order, wakeup handling and tx_gen ordering
A race condition in the Linux kernel CAN ISO-TP protocol can cause system instability or denial of service due to improper timer and state handling.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-80889?
CVE-2026-80889 is a vulnerability in Linux, published on 4 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-80889?
How do I fix CVE-2026-80889?
Apply the vendor's patch.
Is CVE-2026-80889 being exploited?
There is no known exploitation of CVE-2026-80889 in the wild and no public exploit code.
Sources
Also known as AZL-99479, BELL-CVE-2026-80889, DEBIAN-CVE-2026-80889, GHSA-r952-5653-4wq2, UBUNTU-CVE-2026-80889.