Description

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_...

Classification

CVE ID: CVE-2025-21809

Affected Products

Vendor: Linux, Linux

Product: Linux, Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.01% (probability of being exploited)

EPSS Percentile: 1.28% (scored less or equal to compared to others)

EPSS Date: 2025-03-28 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-21809
https://git.kernel.org/stable/c/10ba5a3d57af20e494e0d979d1894260989235dd
https://git.kernel.org/stable/c/0e77dd41689637ac4e1b8fe0f27541f373640855
https://git.kernel.org/stable/c/79d458c13056559d49b5e41fbc4b6890e68cf65b

Timeline