CVE-2025-68169

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

netpoll: Fix deadlock in memory allocation under spinlock

Fix a AA deadlock in refill_skbs() where memory allocation while holding

skb_pool->lock can trigger a recursive lock acquisition attempt.

The deadlock scenario occurs when the system is under severe memory

pressure:

1. refill_skbs() acquires skb_pool->lock (spinlock)

2. alloc_skb() is called while holding the lock

3. Memory allocator fails and calls slab_out_of_memory()

4. This triggers printk() for the OOM warning

5. The console output path calls netpoll_send_udp()

6. netpoll_send_udp() attempts to acquire the same skb_pool->lock

7. Deadlock: the lock is already held by the same CPU

Call stack:

refill_skbs()

spin_lock_irqsave(&skb_pool->lock) <- lock acquired

__alloc_skb()

kmem_cache_alloc_node_noprof()

slab_out_of_memory()

printk()

console_flush_all()

netpoll_send_udp()

skb_dequeue()

spin_lock_irqsave(&skb_pool->lock) <- deadlock attempt

This bug was exposed by commit 248f6571fd4c51 ("netpoll: Optimize skb

refilling on critical path") which removed refill_skbs() from the

critical path (where nested printk was being deferred), letting nested

printk being called from inside refill_skbs()

Refactor refill_skbs() to never allocate memory while holding

the spinlock.

Another possible solution to fix this problem is protecting the

refill_skbs() from nested printks, basically calling

printk_deferred_{enter,exit}() in refill_skbs(), then, any nested

pr_warn() would be deferred.

I prefer this approach, given I _think_ it might be a good idea to move

the alloc_skb() from GFP_ATOMIC to GFP_KERNEL in the future, so, having

the alloc_skb() outside of the lock will be necessary step.

There is a possible TOCTOU issue when checking for the pool length, and

queueing the new allocated skb, but, this is not an issue, given that

an extra SKB in the pool is harmless and it will be eventually used.