------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28, CPU#0: syz.1.462/7117
Modules linked in:
CPU: 0 UID: 0 PID: 7117 Comm: syz.1.462 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28
Code: 06 e8 30 5b e2 fc 48 8d 3d 39 33 26 0c 67 48 0f b9 3a e8 1f 5b e2 fc 5b 5d c3 cc cc cc cc e8 13 5b e2 fc 48 8d 3d 2c 33 26 0c <67> 48 0f b9 3a e8 02 5b e2 fc 5b 5d e9 4b e5 a8 06 e8 f6 5a e2 fc
RSP: 0018:ffffc90000007c18 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88807db0c820 RCX: 0000000000000101
RDX: ffff88802ff42580 RSI: ffffffff852990fd RDI: ffffffff914fc430
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000003 R11: 0000000000000001 R12: ffff88807db0c820
R13: 8000000000000101 R14: 1ffff92000000f8d R15: ffffffff8b056440
FS:  0000000000000000(0000) GS:ffff888123b64000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1543bc2d58 CR3: 000000007c98b000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 __refcount_sub_and_test include/linux/refcount.h:400 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 sctp_transport_put+0x134/0x180 net/sctp/transport.c:476
 call_timer_fn+0x198/0x5f0 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers+0x757/0xb00 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+0x1e6/0x9d0 kernel/softirq.c:645
 __do_softirq kernel/softirq.c:679 [inline]
 invoke_softirq kernel/softirq.c:519 [inline]
 __irq_exit_rcu+0x194/0x210 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+0xa3/0xc0 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:its_return_thunk+0x0/0x10 arch/x86/lib/retpoline.S:437
Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc <c3> cc 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 e9 cb a3 a3 f5 cc
RSP: 0018:ffffc9000584f458 EFLAGS: 00000293
RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffffffff828b51c6
RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff88802ff42580
RBP: 0000000000000001 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: ffff88801f42b160
R13: 0000000000000001 R14: 0000000000000000 R15: dffffc0000000000
 rcu_read_unlock include/linux/rcupdate.h:878 [inline]
 page_table_check_clear+0x2d6/0x540 mm/page_table_check.c:89
 __page_table_check_pte_clear+0x10f/0x120 mm/page_table_check.c:155
 page_table_check_pte_clear include/linux/page_table_check.h:55 [inline]
 ptep_get_and_clear_full arch/x86/include/asm/pgtable.h:1259 [inline]
 get_and_clear_full_ptes include/linux/pgtable.h:879 [inline]
 zap_present_folio_ptes mm/memory.c:1779 [inline]
 zap_present_ptes mm/memory.c:1861 [inline]
 do_zap_pte_range mm/memory.c:1963 [inline]
 zap_pte_range mm/memory.c:2065 [inline]
 zap_pmd_range mm/memory.c:2151 [inline]
 zap_pud_range mm/memory.c:2179 [inline]
 zap_p4d_range mm/memory.c:2200 [inline]
 __zap_vma_range+0x2c43/0x48e0 mm/memory.c:2240
 unmap_vmas+0x299/0x5f0 mm/memory.c:2309
 exit_mmap+0x1ef/0xa00 mm/mmap.c:1315
 __mmput+0x12a/0x410 kernel/fork.c:1193
 mmput+0x67/0x80 kernel/fork.c:1216
 exit_mm kernel/exit.c:614 [inline]
 do_exit+0x8b1/0x2ae0 kernel/exit.c:996
 do_group_exit+0xd5/0x2a0 kernel/exit.c:1151
 get_signal+0x1ec7/0x21e0 kernel/signal.c:3039
 arch_do_signal_or_restart+0x91/0x7e0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
 exit_to_user_mode_loop+0x139/0x700 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:336 [inline]
 do_syscall_64+0x661/0x790 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7d6319e159
Code: Unable to access opcode bytes at 0x7f7d6319e12f.
RSP: 002b:00007f7d641470e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f7d63425fa8 RCX: 00007f7d6319e159
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f7d63425fa8
RBP: 00007f7d63425fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7d63426038 R14: 00007ffc0dc62350 R15: 00007ffc0dc62438
 </TASK>
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	e8 30 5b e2 fc       	call   0xfce25b35
   5:	48 8d 3d 39 33 26 0c 	lea    0xc263339(%rip),%rdi        # 0xc263345
   c:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  11:	e8 1f 5b e2 fc       	call   0xfce25b35
  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 13 5b e2 fc       	call   0xfce25b35
  22:	48 8d 3d 2c 33 26 0c 	lea    0xc26332c(%rip),%rdi        # 0xc263355
* 29:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2e:	e8 02 5b e2 fc       	call   0xfce25b35
  33:	5b                   	pop    %rbx
  34:	5d                   	pop    %rbp
  35:	e9 4b e5 a8 06       	jmp    0x6a8e585
  3a:	e8 f6 5a e2 fc       	call   0xfce25b35