* [PATCH net 1/1] net/sched: act_api: use RCU with deferred freeing for action lifecycle
@ 2026-05-30 11:55 Jamal Hadi Salim
2026-05-30 20:00 ` [syzbot ci] " syzbot ci
0 siblings, 1 reply; 2+ messages in thread
From: Jamal Hadi Salim @ 2026-05-30 11:55 UTC (permalink / raw)
To: netdev
Cc: davem, edumazet, kuba, pabeni, horms, victor, kylebot, jiri,
vladbu, linux-kernel, security, Jamal Hadi Salim
When NEWTFILTER and DELFILTER are run concurently it is possible to create a
race with an associated action.
Let's illustrate with CPU0 running NEWTFILTER and CPU1 running DELFILTER:
0: mutex_lock() <-- holds the idr lock
0: rcu_read_lock()
0: p = idr_find(idr, index) <-- action p is valid (RCU protects IDR)
0: mutex_unlock() <-- releases the idr lock
1: refcount_dec_and_mutex_lock() <-- refcnt 1->0, mutex held
1: idr_remove(idr, index) <-- Action removed from IDR
1: mutex_unlock() <-- mutex released allowing us to delete the action
1: tcf_action_cleanup(p) <-- Kfrees p immediately, no deferral
0: refcount_inc_not_zero(&p->tcfa_refcnt) <-- ouch, UAF p points to freed memory
This patch fixes the race condition between NEWTFILTER and DELTFILTER by
adding struct rcu_head to tc_action used in the deferral and introducing a
kfree_cpu() in the delete path to defer the delete.
Let's illustrate the new code path:
0: rcu_read_lock()
1: refcount_dec_and_mutex_lock() <-- refcnt 1->0, mutex held
1: idr_remove(idr, index)
1: mutex_unlock()
1: kfree_rcu(p, rcu_head) <-- defer to eventually call tcf_action_cleanup()
0: p = idr_find(idr, index)
0: refcount_inc_not_zero(&p->tcfa_refcnt) <-- refcnt 0->1 (object stay alive)
1: rcu_read_unlock() <-- release so freeing can run after grace period
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Reported-by: Kyle Zeng <kylebot@openai.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Tested-by: Kyle Zeng <kylebot@openai.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
include/net/act_api.h | 1 +
net/sched/act_api.c | 14 +++++++++++---
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/include/net/act_api.h b/include/net/act_api.h
index d11b79107930..fd2967ee08f7 100644
--- a/include/net/act_api.h
+++ b/include/net/act_api.h
@@ -45,6 +45,7 @@ struct tc_action {
struct tc_cookie __rcu *user_cookie;
struct tcf_chain __rcu *goto_chain;
u32 tcfa_flags;
+ struct rcu_head tcfa_rcu;
u8 hw_stats;
u8 used_hw_stats;
bool used_hw_stats_valid;
diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 332fd9695e54..3148142bb543 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -370,6 +370,14 @@ static void tcf_action_cleanup(struct tc_action *p)
free_tcf(p);
}
+/* RCU callback to free action after grace period */
+static void tcf_action_rcu_free(struct rcu_head *rcu)
+{
+ struct tc_action *p = container_of(rcu, struct tc_action, tcfa_rcu);
+
+ tcf_action_cleanup(p);
+}
+
static int __tcf_action_put(struct tc_action *p, bool bind)
{
struct tcf_idrinfo *idrinfo = p->idrinfo;
@@ -379,8 +387,8 @@ static int __tcf_action_put(struct tc_action *p, bool bind)
atomic_dec(&p->tcfa_bindcnt);
idr_remove(&idrinfo->action_idr, p->tcfa_index);
mutex_unlock(&idrinfo->lock);
+ call_rcu(&p->tcfa_rcu, tcf_action_rcu_free);
- tcf_action_cleanup(p);
return 1;
}
@@ -620,7 +628,7 @@ static int tcf_idr_release_unsafe(struct tc_action *p)
if (refcount_dec_and_test(&p->tcfa_refcnt)) {
idr_remove(&p->idrinfo->action_idr, p->tcfa_index);
- tcf_action_cleanup(p);
+ call_rcu(&p->tcfa_rcu, tcf_action_rcu_free);
return ACT_P_DELETED;
}
@@ -761,7 +769,7 @@ static int tcf_idr_delete_index(struct tcf_idrinfo *idrinfo, u32 index)
p->tcfa_index));
mutex_unlock(&idrinfo->lock);
- tcf_action_cleanup(p);
+ call_rcu(&p->tcfa_rcu, tcf_action_rcu_free);
module_put(owner);
return 0;
}
--
2.34.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [syzbot ci] Re: net/sched: act_api: use RCU with deferred freeing for action lifecycle
2026-05-30 11:55 [PATCH net 1/1] net/sched: act_api: use RCU with deferred freeing for action lifecycle Jamal Hadi Salim
@ 2026-05-30 20:00 ` syzbot ci
0 siblings, 0 replies; 2+ messages in thread
From: syzbot ci @ 2026-05-30 20:00 UTC (permalink / raw)
To: davem, edumazet, horms, jhs, jiri, kuba, kylebot, linux-kernel,
netdev, pabeni, security, victor, vladbu
Cc: syzbot, syzkaller-bugs
syzbot ci has tested the following series
[v1] net/sched: act_api: use RCU with deferred freeing for action lifecycle
https://lore.kernel.org/all/20260530115511.1352487-1-jhs@mojatatu.com
* [PATCH net 1/1] net/sched: act_api: use RCU with deferred freeing for action lifecycle
and found the following issues:
* BUG: sleeping function called from invalid context in __tcf_chain_put
* inconsistent lock state in tcf_mirred_release
Full report is available here:
https://ci.syzbot.org/series/526aa788-9a02-4038-b101-5daf4d3436a2
***
BUG: sleeping function called from invalid context in __tcf_chain_put
tree: net
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net.git
base: 78ef59e7a6459b16f8102e0ee1c718443323d1af
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/46884a04-6831-455e-8868-d463d6e018db/config
syz repro: https://ci.syzbot.org/findings/3fb6310c-78f8-44da-bd19-4acd582420fa/syz_repro
BUG: sleeping function called from invalid context at kernel/locking/mutex.c:623
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 23, name: ksoftirqd/1
preempt_count: 100, expected: 0
RCU nest depth: 0, expected: 0
1 lock held by ksoftirqd/1/23:
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_do_batch kernel/rcu/tree.c:2611 [inline]
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_core+0x751/0x1070 kernel/rcu/tree.c:2869
Preemption disabled at:
[<ffffffff8187d090>] softirq_handle_begin kernel/softirq.c:463 [inline]
[<ffffffff8187d090>] handle_softirqs+0xb0/0x840 kernel/softirq.c:598
CPU: 1 UID: 0 PID: 23 Comm: ksoftirqd/1 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
__might_resched+0x378/0x4d0 kernel/sched/core.c:9163
__mutex_lock_common kernel/locking/mutex.c:623 [inline]
__mutex_lock+0x11c/0x1550 kernel/locking/mutex.c:820
__tcf_chain_put+0x60/0x820 net/sched/cls_api.c:694
free_tcf net/sched/act_api.c:130 [inline]
tcf_action_cleanup net/sched/act_api.c:370 [inline]
tcf_action_rcu_free+0x39d/0x440 net/sched/act_api.c:378
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
kthread+0x389/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
=============================
[ BUG: Invalid wait context ]
syzkaller #0 Tainted: G W
-----------------------------
ksoftirqd/1/23 is trying to lock:
ffff888171e3b0b0 (&block->lock){+.+.}-{4:4}, at: __tcf_chain_put+0x60/0x820 net/sched/cls_api.c:694
other info that might help us debug this:
context-{3:3}
1 lock held by ksoftirqd/1/23:
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_do_batch kernel/rcu/tree.c:2611 [inline]
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_core+0x751/0x1070 kernel/rcu/tree.c:2869
stack backtrace:
CPU: 1 UID: 0 PID: 23 Comm: ksoftirqd/1 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_lock_invalid_wait_context kernel/locking/lockdep.c:4830 [inline]
check_wait_context kernel/locking/lockdep.c:4902 [inline]
__lock_acquire+0xec1/0x2cf0 kernel/locking/lockdep.c:5187
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a3/0x1550 kernel/locking/mutex.c:820
__tcf_chain_put+0x60/0x820 net/sched/cls_api.c:694
free_tcf net/sched/act_api.c:130 [inline]
tcf_action_cleanup net/sched/act_api.c:370 [inline]
tcf_action_rcu_free+0x39d/0x440 net/sched/act_api.c:378
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
kthread+0x389/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
BUG: sleeping function called from invalid context at kernel/locking/mutex.c:623
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/1
preempt_count: 101, expected: 0
RCU nest depth: 0, expected: 0
INFO: lockdep is turned off.
Preemption disabled at:
[<0000000000000000>] 0x0
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<IRQ>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
__might_resched+0x378/0x4d0 kernel/sched/core.c:9163
__mutex_lock_common kernel/locking/mutex.c:623 [inline]
__mutex_lock+0x11c/0x1550 kernel/locking/mutex.c:820
__tcf_chain_put+0x60/0x820 net/sched/cls_api.c:694
free_tcf net/sched/act_api.c:130 [inline]
tcf_action_cleanup net/sched/act_api.c:370 [inline]
tcf_action_rcu_free+0x39d/0x440 net/sched/act_api.c:378
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xca/0x220 kernel/softirq.c:735
irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1061
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:63
Code: 2b 7d 02 c3 cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d 03 c2 1f 00 fb f4 <e9> 7c f7 02 00 cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90
RSP: 0018:ffffc90000197e20 EFLAGS: 00000246
RAX: ffff8882a9286000 RBX: ffffffff819a857a RCX: 0000000080000001
RDX: 0000000000000001 RSI: ffffffff8c28b7c0 RDI: ffffffff819a857a
RBP: ffffc90000197f10 R08: ffff88823c6339db R09: 1ffff110478c673b
R10: dffffc0000000000 R11: ffffed10478c673c R12: 0000000000000001
R13: 1ffff1102c09e000 R14: 0000000000000001 R15: 1ffff1102c09e000
arch_safe_halt arch/x86/kernel/process.c:766 [inline]
default_idle+0x9/0x20 arch/x86/kernel/process.c:767
default_idle_call+0x72/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:199 [inline]
do_idle+0x36a/0x5f0 kernel/sched/idle.c:352
cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:451
start_secondary+0x101/0x110 arch/x86/kernel/smpboot.c:312
common_startup_64+0x13e/0x147
</TASK>
BUG: sleeping function called from invalid context at kernel/locking/mutex.c:623
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 5742, name: syz-executor
preempt_count: 100, expected: 0
RCU nest depth: 0, expected: 0
INFO: lockdep is turned off.
Preemption disabled at:
[<ffffffff8187d090>] softirq_handle_begin kernel/softirq.c:463 [inline]
[<ffffffff8187d090>] handle_softirqs+0xb0/0x840 kernel/softirq.c:598
CPU: 1 UID: 0 PID: 5742 Comm: syz-executor Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<IRQ>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
__might_resched+0x378/0x4d0 kernel/sched/core.c:9163
__mutex_lock_common kernel/locking/mutex.c:623 [inline]
__mutex_lock+0x11c/0x1550 kernel/locking/mutex.c:820
__tcf_chain_put+0x60/0x820 net/sched/cls_api.c:694
free_tcf net/sched/act_api.c:130 [inline]
tcf_action_cleanup net/sched/act_api.c:370 [inline]
tcf_action_rcu_free+0x39d/0x440 net/sched/act_api.c:378
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xca/0x220 kernel/softirq.c:735
irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1061
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:qlink_to_object mm/kasan/quarantine.c:140 [inline]
RIP: 0010:qlink_free mm/kasan/quarantine.c:145 [inline]
RIP: 0010:qlist_free_all+0x6f/0x100 mm/kasan/quarantine.c:179
Code: 49 8b 44 04 08 89 c2 83 e2 01 48 ff ca 48 09 c2 48 21 ca 0f b6 42 33 c1 e0 18 3d 00 00 00 f5 49 0f 45 d5 4c 8b 62 08 49 8b 2f <49> 63 84 24 b8 00 00 00 49 29 c7 4c 89 e7 4c 89 fe e8 4b e4 ff ff
RSP: 0018:ffffc90003e9f440 EFLAGS: 00000246
RAX: 00000000f5000000 RBX: ffffc90003e9f478 RCX: ffffea0005c84b40
RDX: ffffea0005c84b40 RSI: ffffea00044f5600 RDI: ffff88817212d150
RBP: ffff88817263e598 R08: 0000000000000000 R09: ffffffff82310b6e
R10: dffffc0000000000 R11: fffffbfff2061c3f R12: ffff888160417b40
R13: 0000000000000000 R14: 0000000000000000 R15: ffff88817212d150
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4570 [inline]
slab_alloc_node mm/slub.c:4899 [inline]
__do_kmalloc_node mm/slub.c:5295 [inline]
__kmalloc_node_noprof+0x498/0x7c0 mm/slub.c:5302
kmalloc_node_noprof include/linux/slab.h:1081 [inline]
__vmalloc_area_node mm/vmalloc.c:3857 [inline]
__vmalloc_node_range_noprof+0x5ef/0x1750 mm/vmalloc.c:4064
__vmalloc_node_noprof mm/vmalloc.c:4124 [inline]
vzalloc_noprof+0xb2/0xe0 mm/vmalloc.c:4202
alloc_counters+0x64/0x5d0 net/ipv4/netfilter/ip_tables.c:799
copy_entries_to_user net/ipv4/netfilter/ip_tables.c:821 [inline]
get_entries net/ipv4/netfilter/ip_tables.c:1022 [inline]
do_ipt_get_ctl+0xada/0x1240 net/ipv4/netfilter/ip_tables.c:1668
nf_getsockopt+0x26e/0x290 net/netfilter/nf_sockopt.c:116
ip_getsockopt+0x19e/0x230 net/ipv4/ip_sockglue.c:1777
do_sock_getsockopt+0x51d/0x7e0 net/socket.c:2487
__sys_getsockopt net/socket.c:2518 [inline]
__do_sys_getsockopt net/socket.c:2525 [inline]
__se_sys_getsockopt net/socket.c:2522 [inline]
__x64_sys_getsockopt+0x1a4/0x240 net/socket.c:2522
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0x560 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f326419e62a
Code: 48 83 ec 10 89 d2 48 63 ff 45 31 c9 6a 2a 45 31 c0 31 c9 e8 d8 99 fb ff 48 83 c4 18 c3 0f 1f 00 49 89 ca b8 37 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 06 c3 0f 1f 44 00 00 48 c7 c2 e8 ff ff ff f7
RSP: 002b:00007ffd38f686c8 EFLAGS: 00000216 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 00007ffd38f68750 RCX: 00007f326419e62a
RDX: 0000000000000041 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000000003 R08: 00007ffd38f686ec R09: ff78736871746264
R10: 00007ffd38f68750 R11: 0000000000000216 R12: 00007f32643ecac0
R13: 00007ffd38f686ec R14: 0000000000000000 R15: 00007f32643ed180
</TASK>
BUG: sleeping function called from invalid context at kernel/locking/mutex.c:623
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 23, name: ksoftirqd/1
preempt_count: 100, expected: 0
RCU nest depth: 0, expected: 0
INFO: lockdep is turned off.
Preemption disabled at:
[<ffffffff8187d090>] softirq_handle_begin kernel/softirq.c:463 [inline]
[<ffffffff8187d090>] handle_softirqs+0xb0/0x840 kernel/softirq.c:598
CPU: 1 UID: 0 PID: 23 Comm: ksoftirqd/1 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
__might_resched+0x378/0x4d0 kernel/sched/core.c:9163
__mutex_lock_common kernel/locking/mutex.c:623 [inline]
__mutex_lock+0x11c/0x1550 kernel/locking/mutex.c:820
__tcf_chain_put+0x60/0x820 net/sched/cls_api.c:694
free_tcf net/sched/act_api.c:130 [inline]
tcf_action_cleanup net/sched/act_api.c:370 [inline]
tcf_action_rcu_free+0x39d/0x440 net/sched/act_api.c:378
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
kthread+0x389/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
----------------
Code disassembly (best guess):
0: 2b 7d 02 sub 0x2(%rbp),%edi
3: c3 ret
4: cc int3
5: cc int3
6: cc int3
7: cc int3
8: cc int3
9: cc int3
a: cc int3
b: 90 nop
c: 90 nop
d: 90 nop
e: 90 nop
f: 90 nop
10: 90 nop
11: 90 nop
12: 90 nop
13: 90 nop
14: 90 nop
15: 90 nop
16: 90 nop
17: 90 nop
18: 90 nop
19: 90 nop
1a: 90 nop
1b: f3 0f 1e fa endbr64
1f: eb 07 jmp 0x28
21: 0f 00 2d 03 c2 1f 00 verw 0x1fc203(%rip) # 0x1fc22b
28: fb sti
29: f4 hlt
* 2a: e9 7c f7 02 00 jmp 0x2f7ab <-- trapping instruction
2f: cc int3
30: cc int3
31: cc int3
32: cc int3
33: cc int3
34: cc int3
35: cc int3
36: cc int3
37: cc int3
38: cc int3
39: cc int3
3a: cc int3
3b: 90 nop
3c: 90 nop
3d: 90 nop
3e: 90 nop
3f: 90 nop
***
inconsistent lock state in tcf_mirred_release
tree: net
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net.git
base: 78ef59e7a6459b16f8102e0ee1c718443323d1af
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/46884a04-6831-455e-8868-d463d6e018db/config
syz repro: https://ci.syzbot.org/findings/339567f1-aefa-440b-b74d-8584664a549d/syz_repro
================================
WARNING: inconsistent lock state
syzkaller #0 Not tainted
--------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
ksoftirqd/1/23 [HC0[0]:SC1[1]:HE1:SE0] takes:
ffffffff8fe24698 (mirred_list_lock){+.?.}-{3:3}, at: spin_lock include/linux/spinlock.h:342 [inline]
ffffffff8fe24698 (mirred_list_lock){+.?.}-{3:3}, at: tcf_mirred_release+0x2c/0x1c0 net/sched/act_mirred.c:78
{SOFTIRQ-ON-W} state was registered at:
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
spin_lock include/linux/spinlock.h:342 [inline]
mirred_device_event+0x80/0x2c0 net/sched/act_mirred.c:561
notifier_call_chain+0x1ad/0x3d0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2287 [inline]
call_netdevice_notifiers net/core/dev.c:2301 [inline]
unregister_netdevice_many_notify+0x17a5/0x22c0 net/core/dev.c:12421
ops_exit_rtnl_list net/core/net_namespace.c:187 [inline]
ops_undo_list+0x3d3/0x940 net/core/net_namespace.c:248
cleanup_net+0x56b/0x800 net/core/net_namespace.c:702
process_one_work kernel/workqueue.c:3314 [inline]
process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478
kthread+0x389/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
irq event stamp: 953728
hardirqs last enabled at (953728): [<ffffffff8bac5040>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline]
hardirqs last enabled at (953728): [<ffffffff8bac5040>] _raw_spin_unlock_irqrestore+0x30/0x80 kernel/locking/spinlock.c:198
hardirqs last disabled at (953727): [<ffffffff8bac4e9a>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:130 [inline]
hardirqs last disabled at (953727): [<ffffffff8bac4e9a>] _raw_spin_lock_irqsave+0x1a/0x60 kernel/locking/spinlock.c:166
softirqs last enabled at (953336): [<ffffffff8187fb46>] run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
softirqs last disabled at (953341): [<ffffffff8187fb46>] run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(mirred_list_lock);
<Interrupt>
lock(mirred_list_lock);
*** DEADLOCK ***
1 lock held by ksoftirqd/1/23:
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_do_batch kernel/rcu/tree.c:2611 [inline]
#0: ffffffff8e95ce00 (rcu_callback){....}-{0:0}, at: rcu_core+0x751/0x1070 kernel/rcu/tree.c:2869
stack backtrace:
CPU: 1 UID: 0 PID: 23 Comm: ksoftirqd/1 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_usage_bug+0x28b/0x2e0 kernel/locking/lockdep.c:4042
valid_state kernel/locking/lockdep.c:4056 [inline]
mark_lock_irq+0x410/0x420 kernel/locking/lockdep.c:-1
mark_lock+0x115/0x190 kernel/locking/lockdep.c:4753
mark_usage kernel/locking/lockdep.c:-1 [inline]
__lock_acquire+0x689/0x2cf0 kernel/locking/lockdep.c:5191
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
spin_lock include/linux/spinlock.h:342 [inline]
tcf_mirred_release+0x2c/0x1c0 net/sched/act_mirred.c:78
tcf_action_cleanup net/sched/act_api.c:367 [inline]
tcf_action_rcu_free+0x2bd/0x440 net/sched/act_api.c:378
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
kthread+0x389/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
***
If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syzbot@syzkaller.appspotmail.com
---
This report is generated by a bot. It may contain errors.
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2026-05-30 11:55 [PATCH net 1/1] net/sched: act_api: use RCU with deferred freeing for action lifecycle Jamal Hadi Salim
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