CVE-2026-72126can: isotp: use unconditional synchronize_rcu() in isotp_release()

Official description

In the Linux kernel, the following vulnerability has been resolved: can: isotp: use unconditional synchronize_rcu() in isotp_release() isotp_notify() unregisters the (RCU) CAN filters via can_rx_unregister() and clears so->bound without waiting for a grace period. isotp_release() uses so->bound to decide whether it needs to call synchronize_rcu() before cancelling so->rxtimer, so when NETDEV_UNREGISTER runs first it skips that synchronize_rcu() and can cancel the timer while an in-flight isotp_rcv() is still executing and about to re-arm it via isotp_send_fc(), leading to a use-after-free timer callback on the freed socket. sakisho-bot remarked a problem with rtnl_lock held in isotp_notify(), therefore make isotp_release() always call synchronize_rcu() before cancelling the timers, regardless of so->bound. This still closes the original race (isotp_notify() clearing so->bound without waiting for in-flight isotp_rcv() callers before isotp_release() cancels the RX timer) without adding any RCU wait to the netdevice notifier path.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/945d9894502cd9124f5d676181c542ed2000f7c0
• https://git.kernel.org/stable/c/59672aa4bcd8d32172c1ff6a179583981d6acabc
• https://git.kernel.org/stable/c/15413a082df69175c2f96aeab4c26fe1ff7cff03
• https://git.kernel.org/stable/c/6280eda96e0707264849fa7d036fed873c1f8a6d
• https://git.kernel.org/stable/c/cb6abc584a1bfab107ac003d64948a4aef1730aa
• https://git.kernel.org/stable/c/b88a511308779c225005d7994b8744561bdbafbc
• https://git.kernel.org/stable/c/b8278ff605187ef3fa0f2705e93251cce4c4f8ee
• https://git.kernel.org/stable/c/9b1a02e0d980ac6b0e36a90378f847062f81d7e4