[moderation] [sctp?] WARNING: refcount bug in sctp_generate_timeout_event (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0db4941d9dae bpf: Use rcu_read_lock_dont_migrate in bpf_sk..
git tree: bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=172af92f980000
kernel config: https://syzkaller.appspot.com/x/.config?x=1e0e0bf7e51565cd
dashboard link: https://syzkaller.appspot.com/bug?extid=8518025f28c371e68e3c
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [da...@davemloft.net edum...@google.com ho...@kernel.org ku...@kernel.org linux-...@vger.kernel.org linux...@vger.kernel.org lucie...@gmail.com marcelo...@gmail.com net...@vger.kernel.org pab...@redhat.com]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/692372caac28/disk-0db4941d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5518b9303204/vmlinux-0db4941d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/606bc80ec5b8/bzImage-0db4941d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+851802...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 7563 at lib/refcount.c:25 refcount_warn_saturate+0xfa/0x1d0 lib/refcount.c:25
Modules linked in:
CPU: 1 UID: 0 PID: 7563 Comm: syz.3.521 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:refcount_warn_saturate+0xfa/0x1d0 lib/refcount.c:25
Code: 00 00 e8 c9 fb 2f fd 5b 41 5e e9 11 dc ba 06 cc e8 bb fb 2f fd c6 05 87 a1 f8 0a 01 90 48 c7 c7 00 b2 bf 8b e8 f7 19 f3 fc 90 <0f> 0b 90 90 eb d7 e8 9b fb 2f fd c6 05 68 a1 f8 0a 01 90 48 c7 c7
RSP: 0018:ffffc90000a08b48 EFLAGS: 00010246
RAX: 7c4c1f86041de100 RBX: 0000000000000002 RCX: ffff88802da23c80
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000002
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1bfa244 R12: dffffc0000000000
R13: 0000000000000001 R14: ffff888054308004 R15: ffff8880543083c0
FS: 00007f399e4b86c0(0000) GS:ffff888125e27000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f399e497d58 CR3: 0000000032fde000 CR4: 00000000003526f0
Call Trace:
<IRQ>
sctp_generate_timeout_event+0x1c8/0x360 net/sctp/sm_sideeffect.c:284
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:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:723
irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1052 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1052
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:schedule_debug kernel/sched/core.c:5885 [inline]
RIP: 0010:__schedule+0x1b3/0x4cc0 kernel/sched/core.c:6806
Code: f6 48 8b 1b 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 48 89 df e8 24 ce dc f6 48 81 3b 9d 6e ac 57 <0f> 85 b7 18 00 00 45 85 ed 7f 54 49 8d 5e 18 48 89 d8 48 c1 e8 03
RSP: 0018:ffffc90005536be0 EFLAGS: 00000246
RAX: 1ffff92000aa6000 RBX: ffffc90005530000 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: ffffffff8bc060c0 RDI: ffffffff8bc06080
RBP: ffffc90005536df0 R08: ffffffff8f9db437 R09: 1ffffffff1f3b686
R10: dffffc0000000000 R11: fffffbfff1f3b687 R12: ffff888125e27000
R13: 0000000000000001 R14: ffff88802da23c80 R15: 1ffff110170e7568
preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7256
irqentry_exit+0x6f/0x90 kernel/entry/common.c:211
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:lock_acquire+0x175/0x360 kernel/locking/lockdep.c:5872
Code: 00 00 00 00 9c 8f 44 24 30 f7 44 24 30 00 02 00 00 0f 85 cd 00 00 00 f7 44 24 08 00 02 00 00 74 01 fb 65 48 8b 05 5b 1b f3 10 <48> 3b 44 24 58 0f 85 f2 00 00 00 48 83 c4 60 5b 41 5c 41 5d 41 5e
RSP: 0018:ffffc90005536f78 EFLAGS: 00000206
RAX: 7c4c1f86041de100 RBX: 0000000000000000 RCX: 7c4c1f86041de100
RDX: 0000000000000000 RSI: ffffffff8d9cc7dc RDI: ffffffff8bc060e0
RBP: ffffffff8216d87d R08: 0000000000000000 R09: ffffffff8216d87d
R10: ffffc90005536c08 R11: fffff52000aa6d83 R12: 0000000000000000
R13: ffffffff8e255de0 R14: 0000000000000001 R15: 0000000000000246
fs_reclaim_acquire+0x99/0x100 mm/page_alloc.c:4286
might_alloc include/linux/sched/mm.h:318 [inline]
slab_pre_alloc_hook mm/slub.c:4897 [inline]
slab_alloc_node mm/slub.c:5221 [inline]
kmem_cache_alloc_node_noprof+0x48/0x710 mm/slub.c:5297
kmalloc_reserve+0xbd/0x290 net/core/skbuff.c:579
__alloc_skb+0x142/0x2d0 net/core/skbuff.c:670
alloc_skb include/linux/skbuff.h:1383 [inline]
nlmsg_new include/net/netlink.h:1055 [inline]
netlink_ack+0x146/0xa50 net/netlink/af_netlink.c:2489
netlink_rcv_skb+0x28c/0x470 net/netlink/af_netlink.c:2558
nfnetlink_rcv+0x282/0x2590 net/netfilter/nfnetlink.c:669
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:727 [inline]
__sock_sendmsg+0x219/0x270 net/socket.c:742
____sys_sendmsg+0x505/0x830 net/socket.c:2630
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684
__sys_sendmsg net/socket.c:2716 [inline]
__do_sys_sendmsg net/socket.c:2721 [inline]
__se_sys_sendmsg net/socket.c:2719 [inline]
__x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f399d58eec9
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:00007f399e4b8038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f399d7e5fa0 RCX: 00007f399d58eec9
RDX: 0000000000000000 RSI: 0000200000000000 RDI: 000000000000000c
RBP: 00007f399d611f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f399d7e6038 R14: 00007f399d7e5fa0 R15: 00007fff5f9ffbb8
</TASK>
----------------
Code disassembly (best guess):
0: f6 48 8b 1b testb $0x1b,-0x75(%rax)
4: 48 89 d8 mov %rbx,%rax
7: 48 c1 e8 03 shr $0x3,%rax
b: 48 b9 00 00 00 00 00 movabs $0xdffffc0000000000,%rcx
12: fc ff df
15: 80 3c 08 00 cmpb $0x0,(%rax,%rcx,1)
19: 74 08 je 0x23
1b: 48 89 df mov %rbx,%rdi
1e: e8 24 ce dc f6 call 0xf6dcce47
23: 48 81 3b 9d 6e ac 57 cmpq $0x57ac6e9d,(%rbx)
* 2a: 0f 85 b7 18 00 00 jne 0x18e7 <-- trapping instruction
30: 45 85 ed test %r13d,%r13d
33: 7f 54 jg 0x89
35: 49 8d 5e 18 lea 0x18(%r14),%rbx
39: 48 89 d8 mov %rbx,%rax
3c: 48 c1 e8 03 shr $0x3,%rax


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