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WARNING: refcount bug in call_timer_fn (4)

Status: moderation: reported on 2025/02/19 09:54
Subsystems: apparmor perf
[Documentation on labels]
Reported-by: syzbot+8b5e80cec21177f65e1b@syzkaller.appspotmail.com
First crash: 198d, last: 2d17h
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING: refcount bug in call_timer_fn net 13 1 1367d 1367d 0/29 closed as invalid on 2022/01/07 18:56
upstream WARNING: refcount bug in call_timer_fn (3) fs 13 1 298d 294d 0/29 auto-obsoleted due to no activity on 2025/02/05 18:30
upstream WARNING: refcount bug in call_timer_fn (2) acpi 13 1 392d 388d 0/29 auto-obsoleted due to no activity on 2024/11/03 21:47
linux-6.1 WARNING: refcount bug in call_timer_fn 13 1 549d 549d 0/3 auto-obsoleted due to no activity on 2024/06/09 18:08

Sample crash report:
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 6741 at lib/refcount.c:28 refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Modules linked in:
CPU: 0 UID: 0 PID: 6741 Comm: syz.0.210 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Code: 00 ae e2 8b e8 c7 78 bb fc 90 0f 0b 90 90 eb d7 e8 db da f7 fc c6 05 44 a1 c5 0a 01 90 48 c7 c7 60 ae e2 8b e8 a7 78 bb fc 90 <0f> 0b 90 90 eb b7 e8 bb da f7 fc c6 05 21 a1 c5 0a 01 90 48 c7 c7
RSP: 0018:ffffc90000007b88 EFLAGS: 00010246
RAX: 660a4f4756cc7100 RBX: 0000000000000003 RCX: ffff88805a63bc00
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000002
RBP: ffffc90000007c90 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1bfa1ec R12: 1ffff92000000f78
R13: ffff8880582c99b8 R14: ffff8880582c9820 R15: 0000000000000000
FS:  00007f0c603f66c0(0000) GS:ffff888125c1c000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005636acd1b168 CR3: 000000007c99e000 CR4: 00000000003526f0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 call_timer_fn+0x17b/0x5f0 kernel/time/timer.c:1747
 expire_timers kernel/time/timer.c:1798 [inline]
 __run_timers kernel/time/timer.c:2372 [inline]
 __run_timer_base+0x61a/0x860 kernel/time/timer.c:2384
 run_timer_base kernel/time/timer.c:2393 [inline]
 run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403
 handle_softirqs+0x283/0x870 kernel/softirq.c:579
 __do_softirq kernel/softirq.c:613 [inline]
 invoke_softirq kernel/softirq.c:453 [inline]
 __irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1050
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa8/0x110 kernel/locking/spinlock.c:194
Code: 74 05 e8 4b 87 4b f6 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4f f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 93 2e 14 f6 65 8b 05 6c 71 24 07 85 c0 74 40 48 c7 04 24 0e 36
RSP: 0018:ffffc90019d7e1a0 EFLAGS: 00000206
RAX: 660a4f4756cc7100 RBX: 0000000000000a06 RCX: 660a4f4756cc7100
RDX: 0000000000000006 RSI: ffffffff8d9b6a5f RDI: 0000000000000001
RBP: ffffc90019d7e230 R08: ffffffff8fa38037 R09: 1ffffffff1f47006
R10: dffffc0000000000 R11: fffffbfff1f47007 R12: dffffc0000000000
R13: 1ffff920033afc58 R14: ffffffff99d7a798 R15: 1ffff920033afc34
 debug_rcu_head_queue kernel/rcu/rcu.h:237 [inline]
 __call_rcu_common kernel/rcu/tree.c:3108 [inline]
 call_rcu+0xc3/0x9c0 kernel/rcu/tree.c:3243
 __destroy_inode+0x2da/0x670 fs/inode.c:371
 destroy_inode fs/inode.c:394 [inline]
 evict+0x797/0x9c0 fs/inode.c:834
 __dentry_kill+0x209/0x660 fs/dcache.c:669
 dput+0x19f/0x2b0 fs/dcache.c:911
 find_next_child+0x1e5/0x250 fs/libfs.c:600
 __simple_recursive_removal+0x10b/0x510 fs/libfs.c:617
 debugfs_remove+0x5b/0x70 fs/debugfs/inode.c:790
 ieee80211_debugfs_remove_netdev net/mac80211/debugfs_netdev.c:1021 [inline]
 ieee80211_debugfs_recreate_netdev+0xbf/0x1460 net/mac80211/debugfs_netdev.c:1034
 drv_remove_interface+0x1fa/0x590 net/mac80211/driver-ops.c:125
 ieee80211_do_stop+0x15cb/0x1fb0 net/mac80211/iface.c:709
 ieee80211_stop+0x1b1/0x240 net/mac80211/iface.c:814
 __dev_close_many+0x361/0x6f0 net/core/dev.c:1755
 __dev_close net/core/dev.c:1767 [inline]
 __dev_change_flags+0x2c7/0x6d0 net/core/dev.c:9530
 netif_change_flags+0x88/0x1a0 net/core/dev.c:9595
 do_setlink+0xc55/0x41c0 net/core/rtnetlink.c:3143
 rtnl_changelink net/core/rtnetlink.c:3761 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3920 [inline]
 rtnl_newlink+0x160b/0x1c70 net/core/rtnetlink.c:4057
 rtnetlink_rcv_msg+0x7cc/0xb70 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:729
 ____sys_sendmsg+0x505/0x830 net/socket.c:2614
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
 __sys_sendmsg net/socket.c:2700 [inline]
 __do_sys_sendmsg net/socket.c:2705 [inline]
 __se_sys_sendmsg net/socket.c:2703 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0c6218ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0c603f6038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f0c623c5fa0 RCX: 00007f0c6218ebe9
RDX: 0000000000000000 RSI: 0000200000000600 RDI: 0000000000000005
RBP: 00007f0c62211e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0c623c6038 R14: 00007f0c623c5fa0 R15: 00007ffc503fe238
 </TASK>
----------------
Code disassembly (best guess):
   0:	74 05                	je     0x7
   2:	e8 4b 87 4b f6       	call   0xf64b8752
   7:	48 c7 44 24 20 00 00 	movq   $0x0,0x20(%rsp)
   e:	00 00
  10:	9c                   	pushf
  11:	8f 44 24 20          	pop    0x20(%rsp)
  15:	f6 44 24 21 02       	testb  $0x2,0x21(%rsp)
  1a:	75 4f                	jne    0x6b
  1c:	f7 c3 00 02 00 00    	test   $0x200,%ebx
  22:	74 01                	je     0x25
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
* 2a:	e8 93 2e 14 f6       	call   0xf6142ec2 <-- trapping instruction
  2f:	65 8b 05 6c 71 24 07 	mov    %gs:0x724716c(%rip),%eax        # 0x72471a2
  36:	85 c0                	test   %eax,%eax
  38:	74 40                	je     0x7a
  3a:	48                   	rex.W
  3b:	c7                   	.byte 0xc7
  3c:	04 24                	add    $0x24,%al
  3e:	0e                   	(bad)
  3f:	36                   	ss

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/30 11:45 bpf-next 98857d111c53 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-bpf-next-kasan-gce WARNING: refcount bug in call_timer_fn
2025/04/04 21:04 bpf-next 06a22366d6a1 1c4febdb .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-bpf-next-kasan-gce WARNING: refcount bug in call_timer_fn
2025/02/15 09:42 bpf-next a4585442ade5 40a34ec9 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-bpf-next-kasan-gce WARNING: refcount bug in call_timer_fn
2025/06/19 11:00 linux-next 6e5ab6fee68d ed3e87f7 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: refcount bug in call_timer_fn
* Struck through repros no longer work on HEAD.