[syzbot] [sctp?] WARNING: refcount bug in sctp_generate_timeout_event (4)

[syzbot] [sctp?] WARNING: refcount bug in sctp_generate_timeout_event (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    bf1079577a11 Merge tag 'sched_ext-for-7.3-rc1-fixes' of gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17d06d9e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5e4e3a0e188a497e
dashboard link: https://syzkaller.appspot.com/bug?extid=f5baf1a1df3261c2ad8d
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c52dc60311d3/disk-bf107957.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/37591d96a65b/vmlinux-bf107957.xz
kernel image: https://storage.googleapis.com/syzbot-assets/729e80af6e39/bzImage-bf107957.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f5baf1a1df3261c2ad8d@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25, CPU#1: syz.0.2220/13955
Modules linked in:
CPU: 1 UID: 0 PID: 13955 Comm: syz.0.2220 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25
Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 6b d2 e9 fc 48 8d 3d f4 46 a7 0b 67 48 0f b9 3a eb 4a e8 58 d2 e9 fc 48 8d 3d f1 46 a7 0b <67> 48 0f b9 3a eb 37 e8 45 d2 e9 fc 48 8d 3d ee 46 a7 0b 67 48 0f
RSP: 0018:ffffc90000a18c28 EFLAGS: 00010246
RAX: ffffffff84dde548 RBX: 0000000000000002 RCX: ffff88807715be80
RDX: 0000000000000100 RSI: 0000000000000100 RDI: ffffffff90852c40
RBP: 0000000000000000 R08: ffff88807715be80 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000100 R12: dffffc0000000000
R13: 0000000000000001 R14: ffff888020fde004 R15: ffff888020fde640
FS:  00007f4a87be06c0(0000) GS:ffff888124dda000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff55dd92eb8 CR3: 000000005800b000 CR4: 0000000000350ef0
Call Trace:
 <IRQ>
 sctp_generate_timeout_event+0x1c8/0x390 net/sctp/sm_sideeffect.c:284
 call_timer_fn+0x18d/0x5f0 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+0x226/0x860 kernel/softirq.c:645
 __do_softirq kernel/softirq.c:679 [inline]
 invoke_softirq kernel/softirq.c:519 [inline]
 __irq_exit_rcu+0xcb/0x220 kernel/softirq.c:767
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:784
 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:lock_acquire+0x232/0x350 kernel/locking/lockdep.c:5913
Code: ff ff ff e8 a0 a9 40 0a f7 44 24 10 00 02 00 00 0f 84 38 ff ff ff 65 48 8b 05 f2 44 f1 11 48 3b 44 24 50 75 33 fb 48 83 c4 58 <5b> 41 5c 41 5d 41 5e 41 5f 5d e9 ba 25 6d ff cc 48 8d 3d 77 31 da
RSP: 0018:ffffc9000dabfac8 EFLAGS: 00000282
RAX: b29753db72d85c00 RBX: 0000000000000001 RCX: 8000000000000001
RDX: 00000000b866b3b2 RSI: ffffffff8e6fc28f RDI: ffffffff8c6d9380
RBP: ffff88807715be80 R08: 8c00000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: ffff888066f6e418 R12: ffff888066f6e418
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000246
 __raw_spin_lock include/linux/spinlock_api_smp.h:190 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173
 spin_lock include/linux/spinlock.h:347 [inline]
 __io_cq_lock io_uring/io_uring.c:484 [inline]
 __io_submit_flush_completions+0x85/0x10d0 io_uring/io_uring.c:1133
 io_submit_flush_completions io_uring/io_uring.h:253 [inline]
 io_submit_state_end io_uring/io_uring.c:1939 [inline]
 io_submit_sqes+0x1cec/0x2310 io_uring/io_uring.c:2063
 __do_sys_io_uring_enter io_uring/io_uring.c:2637 [inline]
 __se_sys_io_uring_enter+0x35b/0x1bb0 io_uring/io_uring.c:2586
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4a86d9e159
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:00007f4a87bdff38 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
RAX: ffffffffffffffda RBX: 0000200000000340 RCX: 00007f4a86d9e159
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000009
RBP: 0000000000000a12 R08: 0000000000000000 R09: 0000000000000008
R10: 0000000000000000 R11: 0000000000000246 R12: 0000200000000940
R13: 0000200000000948 R14: 0000000000000e26 R15: 0000000000000002
 </TASK>
----------------
Code disassembly (best guess):
   0:	eb 66                	jmp    0x68
   2:	85 db                	test   %ebx,%ebx
   4:	74 3e                	je     0x44
   6:	83 fb 01             	cmp    $0x1,%ebx
   9:	75 4c                	jne    0x57
   b:	e8 6b d2 e9 fc       	call   0xfce9d27b
  10:	48 8d 3d f4 46 a7 0b 	lea    0xba746f4(%rip),%rdi        # 0xba7470b
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 4a                	jmp    0x68
  1e:	e8 58 d2 e9 fc       	call   0xfce9d27b
  23:	48 8d 3d f1 46 a7 0b 	lea    0xba746f1(%rip),%rdi        # 0xba7471b
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 37                	jmp    0x68
  31:	e8 45 d2 e9 fc       	call   0xfce9d27b
  36:	48 8d 3d ee 46 a7 0b 	lea    0xba746ee(%rip),%rdi        # 0xba7472b
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf


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