CVE-2026-53197

Summary

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

xfrm: iptfs: fix ABBA deadlock in iptfs_destroy_state()

iptfs_destroy_state() calls hrtimer_cancel() while holding a spinlock that the timer callback also acquires, leading to an ABBA deadlock on SMP systems.

For the output timer (iptfs_timer):

• iptfs_destroy_state() holds x->lock, calls hrtimer_cancel()
• iptfs_delay_timer() callback takes x->lock

For the drop timer (drop_timer):

• iptfs_destroy_state() holds drop_lock, calls hrtimer_cancel()
• iptfs_drop_timer() callback takes drop_lock

Both timers use HRTIMER_MODE_REL_SOFT, so their callbacks run in softirq context. When hrtimer_cancel() is called for a soft timer that is currently executing on another CPU, hrtimer_cancel_wait_running() spins on softirq_expiry_lock – the same lock held by the softirq running the callback. If the callback is blocked waiting for the spinlock held by the caller of hrtimer_cancel(), a circular dependency forms:

CPU 0: holds lock_A -> waits for softirq_expiry_lock CPU 1: holds softirq_expiry_lock -> waits for lock_A

Fix by calling hrtimer_cancel() before acquiring the respective locks. hrtimer_cancel() is safe to call without holding any lock and will wait for any in-progress callback to complete. For the output timer, the lock is still acquired afterwards to drain the packet queue. For the drop timer, the lock/unlock pair is removed entirely since it only existed to serialize with the timer callback, which hrtimer_cancel() already guarantees.

Found by source code audit.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/a13ca53e47e500854a3b9ec18b5dc83acfec863e
• https://git.kernel.org/stable/c/822b98d354e63e8249e85473c5f3c519f3c9cecc
• https://git.kernel.org/stable/c/c8a8a75b733467b00c08b91a38dbaf207a08ed6e

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