CVE-2025-21809 — rxrpc, afs: Fix peer hash locking vs RCU callback

Affected: Linux

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

rxrpc, afs: Fix peer hash locking vs RCU callback

In its address list, afs now retains pointers to and refs on one or more rxrpc_peer objects. The address list is freed under RCU and at this time, it puts the refs on those peers.

Now, when an rxrpc_peer object runs out of refs, it gets removed from the peer hash table and, for that, rxrpc has to take a spinlock. However, it is now being called from afs's RCU cleanup, which takes place in BH context - but it is just taking an ordinary spinlock.

The put may also be called from non-BH context, and so there exists the possibility of deadlock if the BH-based RCU cleanup happens whilst the hash spinlock is held. This led to the attached lockdep complaint.

Fix this by changing spinlocks of rxnet->peer_hash_lock back to BH-disabling locks.

================================ WARNING: inconsistent lock state 6.13.0-rc5-build2+ #1223 Tainted: G E -------------------------------- inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. swapper/1/0 [HC0[0]:SC1[1]:HE1:SE0] takes: ffff88810babe228 (&rxnet->peer_hash_lock){+.?.}-{3:3}, at: rxrpc_put_peer+0xcb/0x180 {SOFTIRQ-ON-W} state was registered at: mark_usage+0x164/0x180 __lock_acquire+0x544/0x990 lock_acquire.part.0+0x103/0x280 _raw_spin_lock+0x2f/0x40 rxrpc_peer_keepalive_worker+0x144/0x440 process_one_work+0x486/0x7c0 process_sc…

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CVE-2025-21809 — rxrpc, afs: Fix peer hash locking vs RCU callback