------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 6783 at lib/refcount.c:25 refcount_warn_saturate+0x13a/0x1d0 lib/refcount.c:25
Modules linked in:
CPU: 0 UID: 0 PID: 6783 Comm: syz.2.263 Not tainted 6.14.0-syzkaller-g9bae8f4f2168 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
RIP: 0010:refcount_warn_saturate+0x13a/0x1d0 lib/refcount.c:25
Code: 00 6a a1 8c e8 07 88 7d fc 90 0f 0b 90 90 eb b9 e8 cb 67 be fc c6 05 3a e3 44 0b 01 90 48 c7 c7 60 6a a1 8c e8 e7 87 7d fc 90 <0f> 0b 90 90 eb 99 e8 ab 67 be fc c6 05 1b e3 44 0b 01 90 48 c7 c7
RSP: 0018:ffffc90000007b28 EFLAGS: 00010246
RAX: f4de809b98aa7600 RBX: ffff8880738bc004 RCX: ffff88802665da00
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000002 R08: ffffffff81827a12 R09: fffffbfff1d7a978
R10: dffffc0000000000 R11: fffffbfff1d7a978 R12: dffffc0000000000
R13: 0000000000000002 R14: ffff88802a051440 R15: ffff8880738bc000
FS:  00007f7af0ba46c0(0000) GS:ffff888124f96000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00002000000000c0 CR3: 000000007c37c000 CR4: 00000000003526f0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 sctp_generate_timeout_event+0x1ca/0x360 net/sctp/sm_sideeffect.c:284
 call_timer_fn+0x189/0x650 kernel/time/timer.c:1789
 expire_timers kernel/time/timer.c:1840 [inline]
 __run_timers kernel/time/timer.c:2414 [inline]
 __run_timer_base+0x66e/0x8e0 kernel/time/timer.c:2426
 run_timer_base kernel/time/timer.c:2435 [inline]
 run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2445
 handle_softirqs+0x2d6/0x9b0 kernel/softirq.c:579
 __do_softirq kernel/softirq.c:613 [inline]
 invoke_softirq kernel/softirq.c:453 [inline]
 __irq_exit_rcu+0xfb/0x220 kernel/softirq.c:680
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1049
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:arch_check_zapped_pte+0x3a/0xb0 arch/x86/mm/pgtable.c:890
Code: 7c c6 53 00 48 83 c3 20 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 c9 ef bd 00 4c 8b 3b <48> bb 00 00 00 00 20 00 00 00 48 89 de 4c 21 fe 31 ff e8 1f cb 53
RSP: 0018:ffffc9000306f240 EFLAGS: 00000246
RAX: 1ffff110066e0804 RBX: ffff888033704020 RCX: dffffc0000000000
RDX: ffffc9000ccc4000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc9000306f610 R08: ffffffff8211d084 R09: 1ffffd4000394330
R10: dffffc0000000000 R11: fffff94000394331 R12: ffffea0001ca1980
R13: dffffc0000000000 R14: 8000000072866007 R15: 00000000180400fb
 zap_present_folio_ptes mm/memory.c:1518 [inline]
 zap_present_ptes mm/memory.c:1586 [inline]
 do_zap_pte_range mm/memory.c:1687 [inline]
 zap_pte_range mm/memory.c:1731 [inline]
 zap_pmd_range mm/memory.c:1823 [inline]
 zap_pud_range mm/memory.c:1852 [inline]
 zap_p4d_range mm/memory.c:1873 [inline]
 unmap_page_range+0x20d7/0x44d0 mm/memory.c:1894
 unmap_vmas+0x3ce/0x5f0 mm/memory.c:1984
 exit_mmap+0x2bc/0xde0 mm/mmap.c:1284
 __mmput+0x115/0x420 kernel/fork.c:1379
 copy_process+0x2891/0x3d10 kernel/fork.c:2693
 kernel_clone+0x242/0x930 kernel/fork.c:2844
 __do_sys_clone kernel/fork.c:2987 [inline]
 __se_sys_clone kernel/fork.c:2971 [inline]
 __x64_sys_clone+0x268/0x2e0 kernel/fork.c:2971
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7aefd8d169
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:00007f7af0ba3fe8 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f7aeffa5fa0 RCX: 00007f7aefd8d169
RDX: 00002000000000c0 RSI: 0000000000000000 RDI: 0000000082001000
RBP: 00007f7aefe0e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f7aeffa5fa0 R15: 00007ffe033b7728
 </TASK>
----------------
Code disassembly (best guess), 4 bytes skipped:
   0:	48 83 c3 20          	add    $0x20,%rbx
   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 c9 ef bd 00       	call   0xbdefec
  23:	4c 8b 3b             	mov    (%rbx),%r15
* 26:	48 bb 00 00 00 00 20 	movabs $0x2000000000,%rbx <-- trapping instruction
  2d:	00 00 00
  30:	48 89 de             	mov    %rbx,%rsi
  33:	4c 21 fe             	and    %r15,%rsi
  36:	31 ff                	xor    %edi,%edi
  38:	e8                   	.byte 0xe8
  39:	1f                   	(bad)
  3a:	cb                   	lret
  3b:	53                   	push   %rbx