[v6.1] WARNING: refcount bug in sctp_transport_put

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 882efbdd9d34 Linux 6.1.155
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10a38542580000
kernel config: https://syzkaller.appspot.com/x/.config?x=68aa5a3af1cb953a
dashboard link: https://syzkaller.appspot.com/bug?extid=f90465a2483c8fec0bc0
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ace97ceaac60/disk-882efbdd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/88315d1cd2fa/vmlinux-882efbdd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5e607a61f425/Image-882efbdd.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f90465...@syzkaller.appspotmail.com

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refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 7271 at lib/refcount.c:28 refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 7271 Comm: syz.2.687 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
pstate: 62400005 (nZCv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
pc : refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
lr : refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
sp : ffff800008017b60
x29: ffff800008017b60 x28: 1fffe0001a748379 x27: dfff800000000000
x26: ffff700001002f84 x25: dfff800000000000 x24: ffff0000f8ec6300
x23: 0000000000000001 x22: ffff0000d59a1c40 x21: 0000000000000000
x20: ffff0000f57f1820 x19: ffff800017a8a000 x18: ffff800011abbcc0
x17: 0000000000000000 x16: ffff8000082d22e0 x15: 0000000000000000
x14: 00000000ffffffff x13: 0000000000000001 x12: 0000000000ff0100
x11: ff00800008191ca8 x10: 0000000000000000 x9 : 4a7188095fac1000
x8 : 4a7188095fac1000 x7 : 0000000000000001 x6 : 0000000000000001
x5 : ffff8000080175f8 x4 : ffff8000151a4820 x3 : ffff80000852e158
x2 : 0000000000000001 x1 : 0000000000000100 x0 : 0000000000000000
Call trace:
refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
__refcount_sub_and_test include/linux/refcount.h:283 [inline]
__refcount_dec_and_test include/linux/refcount.h:315 [inline]
refcount_dec_and_test include/linux/refcount.h:333 [inline]
sctp_transport_put+0x130/0x174 net/sctp/transport.c:485
sctp_generate_reconf_event+0x258/0x328 net/sctp/sm_sideeffect.c:475
call_timer_fn+0x1b8/0x964 kernel/time/timer.c:1504
expire_timers kernel/time/timer.c:1549 [inline]
__run_timers+0x460/0x6bc kernel/time/timer.c:1820
run_timer_softirq+0x7c/0x114 kernel/time/timer.c:1833
handle_softirqs+0x318/0xc6c kernel/softirq.c:596
__do_softirq+0x14/0x20 kernel/softirq.c:630
____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:80
call_on_irq_stack+0x30/0x48 arch/arm64/kernel/entry.S:897
do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:85
invoke_softirq kernel/softirq.c:477 [inline]
__irq_exit_rcu+0x23c/0x43c kernel/softirq.c:679
irq_exit_rcu+0x14/0x84 kernel/softirq.c:691
__el1_irq arch/arm64/kernel/entry-common.c:472 [inline]
el1_interrupt+0x38/0x54 arch/arm64/kernel/entry-common.c:486
el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:491
el1h_64_irq+0x64/0x68 arch/arm64/kernel/entry.S:581
trace_lock_release include/trace/events/lock.h:69 [inline]
lock_release+0x64/0x910 kernel/locking/lockdep.c:5673
__might_fault+0xf0/0x124 mm/memory.c:5852
do_recvmmsg+0x394/0x96c net/socket.c:2880
__sys_recvmmsg net/socket.c:2953 [inline]
__do_sys_recvmmsg net/socket.c:2976 [inline]
__se_sys_recvmmsg net/socket.c:2969 [inline]
__arm64_sys_recvmmsg+0x17c/0x238 net/socket.c:2969
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
irq event stamp: 112865
hardirqs last enabled at (112864): [<ffff800008308424>] __up_console_sem+0xb4/0x100 kernel/printk/printk.c:261
hardirqs last disabled at (112865): [<ffff80001195a4d8>] el1_dbg+0x24/0x80 arch/arm64/kernel/entry-common.c:405
softirqs last enabled at (107706): [<ffff8000081a967c>] softirq_handle_end kernel/softirq.c:439 [inline]
softirqs last enabled at (107706): [<ffff8000081a967c>] handle_softirqs+0xaf8/0xc6c kernel/softirq.c:624
softirqs last disabled at (112837): [<ffff800008020164>] __do_softirq+0x14/0x20 kernel/softirq.c:630
---[ end trace 0000000000000000 ]---
vkms_vblank_simulate: vblank timer overrun


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