syzbot
possible deadlock in ip_check_mc_rcu
Status:
upstream: reported on 2026/08/26 11:55
Subsystems:
net
Labels:
prio:high
[Documentation on labels]
Reported-by: syzbot+a5a07d2f6a71972dc5ed@syzkaller.appspotmail.com
First crash: 42d, last: 42d
Sample crash report:
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.4.3416/18916 is trying to acquire lock:
ffff888042dfe6b0 (&im->lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:348 [inline]
ffff888042dfe6b0 (&im->lock){+.-.}-{3:3}, at: ip_check_mc_rcu+0x448/0x670 net/ipv4/igmp.c:2869
but task is already holding lock:
ffff8880331d08b0 (&im->lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:348 [inline]
ffff8880331d08b0 (&im->lock){+.-.}-{3:3}, at: igmpv3_send_cr net/ipv4/igmp.c:727 [inline]
ffff8880331d08b0 (&im->lock){+.-.}-{3:3}, at: igmp_ifc_timer_expire+0x852/0x10b0 net/ipv4/igmp.c:843
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&im->lock);
lock(&im->lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
9 locks held by syz.4.3416/18916:
#0: ffffffff9057afc0 (&ops->srcu#2){.+.+}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff9057afc0 (&ops->srcu#2){.+.+}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#0: ffffffff9057afc0 (&ops->srcu#2){.+.+}-{0:0}, at: rtnl_link_ops_get+0x23/0x250 net/core/rtnetlink.c:595
#1: ffffffff9002c240 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
#1: ffffffff9002c240 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:366 [inline]
#1: ffffffff9002c240 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0xc10/0x1c30 net/core/rtnetlink.c:4194
#2: ffffffff8eb4bfa0 (console_lock){+.+.}-{0:0}, at: console_trylock_spinning kernel/printk/printk.c:2026 [inline]
#2: ffffffff8eb4bfa0 (console_lock){+.+.}-{0:0}, at: vprintk_emit+0x2cf/0x560 kernel/printk/printk.c:2478
#3: ffffffff8ea33838 (console_srcu){....}-{0:0}, at: rcu_try_lock_acquire include/linux/rcupdate.h:305 [inline]
#3: ffffffff8ea33838 (console_srcu){....}-{0:0}, at: srcu_read_lock_nmisafe include/linux/srcu.h:428 [inline]
#3: ffffffff8ea33838 (console_srcu){....}-{0:0}, at: console_srcu_read_lock kernel/printk/printk.c:291 [inline]
#3: ffffffff8ea33838 (console_srcu){....}-{0:0}, at: console_flush_one_record kernel/printk/printk.c:3246 [inline]
#3: ffffffff8ea33838 (console_srcu){....}-{0:0}, at: console_flush_all+0x123/0xaf0 kernel/printk/printk.c:3343
#4: ffffc90000a08cc0 ((&in_dev->mr_ifc_timer)){+.-.}-{0:0}, at: call_timer_fn+0xd4/0x5e0 kernel/time/timer.c:1745
#5: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#5: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#5: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: igmpv3_send_cr net/ipv4/igmp.c:689 [inline]
#5: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: igmp_ifc_timer_expire+0x28/0x10b0 net/ipv4/igmp.c:843
#6: ffff8880331d08b0 (&im->lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:348 [inline]
#6: ffff8880331d08b0 (&im->lock){+.-.}-{3:3}, at: igmpv3_send_cr net/ipv4/igmp.c:727 [inline]
#6: ffff8880331d08b0 (&im->lock){+.-.}-{3:3}, at: igmp_ifc_timer_expire+0x852/0x10b0 net/ipv4/igmp.c:843
#7: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#7: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#7: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: xfrm_policy_get_afinfo+0x30/0x1b0 net/xfrm/xfrm_policy.c:263
#8: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#8: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#8: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: ip_route_output_key_hash+0xd8/0x2a0 net/ipv4/route.c:2701
stack backtrace:
CPU: 1 UID: 0 PID: 18916 Comm: syz.4.3416 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
<IRQ>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
check_deadlock kernel/locking/lockdep.c:3093 [inline]
validate_chain kernel/locking/lockdep.c:3895 [inline]
__lock_acquire+0x24df/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:150 [inline]
_raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:182
spin_lock_bh include/linux/spinlock.h:348 [inline]
ip_check_mc_rcu+0x448/0x670 net/ipv4/igmp.c:2869
__mkroute_output net/ipv4/route.c:2600 [inline]
ip_route_output_key_hash_rcu+0xe7f/0x2720 net/ipv4/route.c:2872
ip_route_output_key_hash+0x18d/0x2a0 net/ipv4/route.c:2702
xfrm4_get_saddr+0xb6/0x170 net/ipv4/xfrm4_policy.c:57
xfrm_get_saddr net/xfrm/xfrm_policy.c:2472 [inline]
xfrm_tmpl_resolve_one net/xfrm/xfrm_policy.c:2508 [inline]
xfrm_tmpl_resolve net/xfrm/xfrm_policy.c:2567 [inline]
xfrm_resolve_and_create_bundle+0x6df/0x3070 net/xfrm/xfrm_policy.c:2865
xfrm_bundle_lookup net/xfrm/xfrm_policy.c:3100 [inline]
xfrm_lookup_with_ifid+0x576/0x1b40 net/xfrm/xfrm_policy.c:3231
xfrm_lookup net/xfrm/xfrm_policy.c:3330 [inline]
xfrm_lookup_route+0x3c/0x1c0 net/xfrm/xfrm_policy.c:3341
ip_route_output_ports include/net/route.h:213 [inline]
igmpv3_newpack+0x2a7/0x1190 net/ipv4/igmp.c:402
add_grhead+0x70/0x340 net/ipv4/igmp.c:473
add_grec+0x1123/0x13e0 net/ipv4/igmp.c:607
igmpv3_send_cr net/ipv4/igmp.c:744 [inline]
igmp_ifc_timer_expire+0x93e/0x10b0 net/ipv4/igmp.c:843
call_timer_fn+0x192/0x5e0 kernel/time/timer.c:1748
expire_timers kernel/time/timer.c:1799 [inline]
__run_timers kernel/time/timer.c:2374 [inline]
__run_timer_base+0x652/0x8b0 kernel/time/timer.c:2386
run_timer_base kernel/time/timer.c:2395 [inline]
run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2405
handle_softirqs+0x225/0x840 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:1062 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1062
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:console_flush_one_record arch/x86/include/asm/irqflags.h:-1 [inline]
RIP: 0010:console_flush_all+0x7d2/0xaf0 kernel/printk/printk.c:3343
Code: ff ff e8 71 2d 21 00 90 0f 0b 90 e9 9c fc ff ff e8 63 2d 21 00 e8 3e b0 29 0a 48 85 db 74 c0 e8 54 2d 21 00 fb 48 8b 5c 24 18 <48> 8b 44 24 28 42 80 3c 20 00 4d 8d 77 58 74 08 4c 89 f7 e8 e6 b9
RSP: 0018:ffffc90002fe6840 EFLAGS: 00000283
RAX: ffffffff81a544ec RBX: ffffc90002fe69a0 RCX: 0000000000080000
RDX: ffffc9000db64000 RSI: 0000000000043066 RDI: 0000000000043067
RBP: ffffc90002fe6950 R08: ffffffff905775f7 R09: 1ffffffff20aeebe
R10: dffffc0000000000 R11: fffffbfff20aeebf R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: ffffffff8f46ec20
__console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
console_unlock+0xd1/0x1c0 kernel/printk/printk.c:3413
vprintk_emit+0x485/0x560 kernel/printk/printk.c:2479
_printk+0xdd/0x130 kernel/printk/printk.c:2504
vlan_vid0_add net/8021q/vlan.c:347 [inline]
vlan_device_event+0x13e6/0x1580 net/8021q/vlan.c:388
notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2291 [inline]
call_netdevice_notifiers net/core/dev.c:2305 [inline]
__dev_notify_flags+0x31e/0x510 net/core/dev.c:9798
rtnl_configure_link+0x2f5/0x510 net/core/rtnetlink.c:3712
rtnl_newlink_create+0x343/0x7b0 net/core/rtnetlink.c:3957
__rtnl_newlink net/core/rtnetlink.c:4078 [inline]
rtnl_newlink+0x166d/0x1c30 net/core/rtnetlink.c:4195
rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7112
netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x7bb/0x940 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
__sock_sendmsg net/socket.c:790 [inline]
____sys_sendmsg+0x54e/0x850 net/socket.c:2684
___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
__sys_sendmsg net/socket.c:2770 [inline]
__do_sys_sendmsg net/socket.c:2775 [inline]
__se_sys_sendmsg net/socket.c:2773 [inline]
__x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2773
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff1f559de59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff1f37f6028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007ff1f5825fa0 RCX: 00007ff1f559de59
RDX: 0000000000000000 RSI: 0000200000000080 RDI: 0000000000000006
RBP: 00007ff1f5633e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff1f5826038 R14: 00007ff1f5825fa0 R15: 00007ffdfbb2bc38
</TASK>
GRED: Unable to relocate VQ 0x0 after dequeue, screwing up backlog
----------------
Code disassembly (best guess), 1 bytes skipped:
0: ff ljmp (bad)
1: e8 71 2d 21 00 call 0x212d77
6: 90 nop
7: 0f 0b ud2
9: 90 nop
a: e9 9c fc ff ff jmp 0xfffffcab
f: e8 63 2d 21 00 call 0x212d77
14: e8 3e b0 29 0a call 0xa29b057
19: 48 85 db test %rbx,%rbx
1c: 74 c0 je 0xffffffde
1e: e8 54 2d 21 00 call 0x212d77
23: fb sti
24: 48 8b 5c 24 18 mov 0x18(%rsp),%rbx
* 29: 48 8b 44 24 28 mov 0x28(%rsp),%rax <-- trapping instruction
2e: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1)
33: 4d 8d 77 58 lea 0x58(%r15),%r14
37: 74 08 je 0x41
39: 4c 89 f7 mov %r14,%rdi
3c: e8 .byte 0xe8
3d: e6 b9 out %al,$0xb9
Struck through repros no longer work on HEAD.