[syzbot] [sctp?] WARNING: refcount bug in sctp_association_hold

[syzbot] [sctp?] WARNING: refcount bug in sctp_association_hold

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    c1f49dea2b8f Merge tag 'mm-hotfixes-stable-2026-04-19-00-1..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15de0e6a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=507c1c0a12a79510
dashboard link: https://syzkaller.appspot.com/bug?extid=61bdf856ff699245c643
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: i386

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-c1f49dea.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/98ce9fed1a97/vmlinux-c1f49dea.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b02e163ec959/bzImage-c1f49dea.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+61bdf856ff699245c643@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x111/0x130 lib/refcount.c:25, CPU#0: swapper/0/0
Modules linked in:
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:refcount_warn_saturate+0x111/0x130 lib/refcount.c:25
Code: 06 e8 e3 e8 11 fd 48 8d 3d 8c d6 ef 0b 67 48 0f b9 3a e8 d2 e8 11 fd 5b 5d c3 cc cc cc cc e8 c6 e8 11 fd 48 8d 3d 7f d6 ef 0b <67> 48 0f b9 3a e8 b5 e8 11 fd 5b 5d e9 0e de a2 06 48 89 df e8 a6
RSP: 0000:ffffc90000007bd8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff888075d2e004 RCX: ffffffff84f6dc0b
RDX: ffffffff8e4955c0 RSI: ffffffff84f6dcba RDI: ffffffff90e6b340
RBP: 0000000000000002 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000002 R11: 0000000000000000 R12: ffff888075d2e004
R13: 0000000000000002 R14: ffff88804fd3cbd0 R15: ffff888050620000
FS:  0000000000000000(0000) GS:ffff8880970ee000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000080066018 CR3: 000000004c3cc000 CR4: 0000000000352ef0
Call Trace:
 <IRQ>
 __refcount_add include/linux/refcount.h:289 [inline]
 __refcount_inc include/linux/refcount.h:366 [inline]
 refcount_inc include/linux/refcount.h:383 [inline]
 sctp_association_hold+0x9f/0xb0 net/sctp/associola.c:843
 sctp_generate_timeout_event+0x292/0x3f0 net/sctp/sm_sideeffect.c:284
 call_timer_fn+0x19a/0x640 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers+0x75f/0xaf0 kernel/time/timer.c:2374
 __run_timer_base kernel/time/timer.c:2386 [inline]
 __run_timer_base kernel/time/timer.c:2378 [inline]
 run_timer_base+0x114/0x190 kernel/time/timer.c:2395
 run_timer_softirq+0x1a/0x50 kernel/time/timer.c:2405
 handle_softirqs+0x1ea/0xa00 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x162/0x210 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+0xa3/0xc0 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:steal_cookie_task kernel/sched/core.c:6401 [inline]
RIP: 0010:sched_core_balance+0x3fd/0xea0 kernel/sched/core.c:6422
Code: 7e 48 48 89 4c 24 40 e8 61 df c2 09 48 8b 4c 24 40 e9 3a 01 00 00 49 8d 7f 48 e8 4e df c2 09 e8 79 76 3a 00 fb 80 7c 24 30 00 <0f> 85 92 00 00 00 8d 4d 01 48 63 d1 49 39 d4 73 48 83 f9 08 74 41
RSP: 0000:ffffffff8e407b80 EFLAGS: 00000246
RAX: 000000000046d04f RBX: ffff88802b23b3c8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8df51613 RDI: ffffffff8c1c0200
RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000001
R13: dffffc0000000000 R14: ffff88802b33b380 R15: ffff88802b23b380
 do_balance_callbacks kernel/sched/core.c:5017 [inline]
 __balance_callbacks+0x21d/0x6e0 kernel/sched/core.c:5073
 __schedule+0x31b9/0x6820 kernel/sched/core.c:7191
 schedule_idle+0x54/0x80 kernel/sched/core.c:7308
 do_idle+0x2dd/0x590 kernel/sched/idle.c:381
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:451
 rest_init+0x251/0x260 init/main.c:762
 start_kernel+0x484/0x490 init/main.c:1220
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0x12b/0x130 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x148
 </TASK>
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	e8 e3 e8 11 fd       	call   0xfd11e8e8
   5:	48 8d 3d 8c d6 ef 0b 	lea    0xbefd68c(%rip),%rdi        # 0xbefd698
   c:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  11:	e8 d2 e8 11 fd       	call   0xfd11e8e8
  16:	5b                   	pop    %rbx
  17:	5d                   	pop    %rbp
  18:	c3                   	ret
  19:	cc                   	int3
  1a:	cc                   	int3
  1b:	cc                   	int3
  1c:	cc                   	int3
  1d:	e8 c6 e8 11 fd       	call   0xfd11e8e8
  22:	48 8d 3d 7f d6 ef 0b 	lea    0xbefd67f(%rip),%rdi        # 0xbefd6a8
* 29:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2e:	e8 b5 e8 11 fd       	call   0xfd11e8e8
  33:	5b                   	pop    %rbx
  34:	5d                   	pop    %rbp
  35:	e9 0e de a2 06       	jmp    0x6a2de48
  3a:	48 89 df             	mov    %rbx,%rdi
  3d:	e8                   	.byte 0xe8
  3e:	a6                   	cmpsb  %es:(%rdi),%ds:(%rsi)


---
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