Summary
In the Linux kernel, the following vulnerability has been resolved: rxrpc, afs: Fix peer hash...
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_scheduled_works+0x73/0x90
worker_thread+0x1c8/0x2a0
kthread+0x19b/0x1b0
ret_from_fork+0x24/0x40
ret_from_fork_asm+0x1a/0x30
irq event stamp: 972402
hardirqs last enabled at (972402): [<ffffffff8244360e>] _raw_spin_unlock_irqrestore+0x2e/0x50
hardirqs last disabled at (972401): [<ffffffff82443328>] _raw_spin_lock_irqsave+0x18/0x60
softirqs last enabled at (972300): [<ffffffff810ffbbe>] handle_softirqs+0x3ee/0x430
softirqs last disabled at (972313): [<ffffffff810ffc54>] __irq_exit_rcu+0x44/0x110
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&rxnet->peer_hash_lock);
<Interrupt>
lock(&rxnet->peer_hash_lock);
*** DEADLOCK ***
1 lock held by swapper/1/0:
#0: ffffffff83576be0 (rcu_callback){....}-{0:0}, at: rcu_lock_acquire+0x7/0x30
stack backtrace:
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G E 6.13.0-rc5-build2+ #1223
Tainted: [E]=UNSIGNED_MODULE
Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
Call Trace:
<IRQ>
dump_stack_lvl+0x57/0x80
print_usage_bug.part.0+0x227/0x240
valid_state+0x53/0x70
mark_lock_irq+0xa5/0x2f0
mark_lock+0xf7/0x170
mark_usage+0xe1/0x180
__lock_acquire+0x544/0x990
lock_acquire.part.0+0x103/0x280
_raw_spin_lock+0x2f/0x40
rxrpc_put_peer+0xcb/0x180
afs_free_addrlist+0x46/0x90 [kafs]
rcu_do_batch+0x2d2/0x640
rcu_core+0x2f7/0x350
handle_softirqs+0x1ee/0x430
__irq_exit_rcu+0x44/0x110
irq_exit_rcu+0xa/0x30
sysvec_apic_timer_interrupt+0x7f/0xa0
</IRQ>
Impact
CVE-2025-21809 has a CVSS score of 5.5 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-21809? CVE-2025-21809 is a medium-severity security vulnerability. No fixed version is listed yet.
- How severe is CVE-2025-21809? CVE-2025-21809 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-21809? No fixed version is listed for CVE-2025-21809 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-21809 exploitable, and should I be worried? Whether CVE-2025-21809 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-21809 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.