WARNING: refcount bug in smc_release

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    406715df fq_codel: do not include <linux/jhash.h>
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=174f27f7600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5f15f8f0e3274b14
dashboard link: https://syzkaller.appspot.com/bug?extid=4c063e6dea39e4b79f29
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16a04def600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17e456df600000

The bug was bisected to:

commit 50717a37db032ce783f50685a73bb2ac68471a5a
Author: Ursula Braun <ubraun@xxxxxxxxxxxxx>
Date:   Fri Apr 12 10:57:23 2019 +0000

    net/smc: nonblocking connect rework

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=147c5954e00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=167c5954e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=127c5954e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4c063e6dea39e4b79f29@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 50717a37db03 ("net/smc: nonblocking connect rework")

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 8688 at lib/refcount.c:190  
refcount_sub_and_test_checked lib/refcount.c:190 [inline]
WARNING: CPU: 0 PID: 8688 at lib/refcount.c:190  
refcount_sub_and_test_checked+0x1d0/0x200 lib/refcount.c:180
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 8688 Comm: syz-executor713 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 panic+0x2e3/0x75c kernel/panic.c:221
 __warn.cold+0x2f/0x35 kernel/panic.c:582
 report_bug+0x289/0x300 lib/bug.c:195
 fixup_bug arch/x86/kernel/traps.c:179 [inline]
 fixup_bug arch/x86/kernel/traps.c:174 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
 invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028
RIP: 0010:refcount_sub_and_test_checked lib/refcount.c:190 [inline]
RIP: 0010:refcount_sub_and_test_checked+0x1d0/0x200 lib/refcount.c:180
Code: 1d 24 69 7e 06 31 ff 89 de e8 bc ba 2e fe 84 db 75 94 e8 73 b9 2e fe  
48 c7 c7 00 ae e6 87 c6 05 04 69 7e 06 01 e8 18 fc ff fd <0f> 0b e9 75 ff  
ff ff e8 54 b9 2e fe e9 6e ff ff ff 48 89 df e8 d7
RSP: 0018:ffff88808bb6fcb0 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815cb796 RDI: ffffed101176df88
RBP: ffff88808bb6fd48 R08: ffff8880993b2200 R09: fffffbfff14f0746
R10: fffffbfff14f0745 R11: ffffffff8a783a2f R12: 00000000ffffffff
R13: 0000000000000001 R14: ffff88808bb6fd20 R15: 0000000000000000
 refcount_dec_and_test_checked+0x1b/0x20 lib/refcount.c:220
 sock_put include/net/sock.h:1729 [inline]
 smc_release+0x236/0x3e0 net/smc/af_smc.c:194
 __sock_release+0xce/0x280 net/socket.c:590
 sock_close+0x1e/0x30 net/socket.c:1268
 __fput+0x2ff/0x890 fs/file_table.c:280
 ____fput+0x16/0x20 fs/file_table.c:313
 task_work_run+0x145/0x1c0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:163
 prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
 do_syscall_64+0x65f/0x760 arch/x86/entry/common.c:300
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x401fb0
Code: 01 f0 ff ff 0f 83 40 0d 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f  
44 00 00 83 3d 7d 8b 2d 00 00 75 14 b8 03 00 00 00 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 14 0d 00 00 c3 48 83 ec 08 e8 7a 02 00 00
RSP: 002b:00007fff583762f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000401fb0
RDX: 0000000000000017 RSI: 0000000000000006 RDI: 0000000000000003
RBP: 0000000000010b24 R08: 0000000000000004 R09: 0000000500000000
R10: 0000000020000240 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000004031e0 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


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