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

sctp: fix a TOCTOU race in SCTP_CMD_TIMER_START

The SCTP_CMD_TIMER_START handler checks timer_pending() before calling
timer_reduce(). The timer can expire and detach between these operations,
causing timer_reduce() to rearm the timer without taking the association
reference required for the newly armed timer.

The timer callback later unconditionally drops its association reference,
which can leave the association reference count unbalanced and result in
use-after-free during association teardown.

Use the return value of timer_reduce() to determine whether the timer was
actually armed. Take the association reference only when timer_reduce()
successfully starts a new timer, closing the race between checking the
timer state and rearming it.

This issue was reported by Nico Yip (@_cyeaa_) working with TrendAI Zero
Day Initiative.