Subject: WARNING: refcount bug in smc_release (3)

From: syzbot <[email-masked]>
Date: Tue, 08 Sep 2020 00:33:19 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    15bc20c6 Merge tag 'tty-5.9-rc3' of git://git.kernel.org/p..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=114602f2900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=978db74cb30aa994
dashboard link: https://syzkaller.appspot.com/bug?extid=8b963fe6ec74e5dac8d7
compiler:       gcc (GCC) 10.1.0-syz 20200507

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 28422 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 28422 Comm: syz-executor.3 Not tainted 5.9.0-rc2-syzkaller #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+0x18f/0x20d lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:231
 __warn.cold+0x20/0x4a kernel/panic.c:600
 report_bug+0x1bd/0x210 lib/bug.c:198
 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
 exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Code: 07 31 ff 89 de e8 97 d2 d8 fd 84 db 0f 85 36 ff ff ff e8 4a d6 d8 fd 48 c7 c7 a0 da 93 88 c6 05 43 e5 11 07 01 e8 39 e7 a9 fd <0f> 0b e9 17 ff ff ff e8 2b d6 d8 fd 0f b6 1d 28 e5 11 07 31 ff 89
RSP: 0018:ffffc90017fafdd8 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff8880477d43c0 RSI: ffffffff815dafc7 RDI: fffff52002ff5fad
RBP: 0000000000000002 R08: 0000000000000001 R09: ffff8880ae720f8b
R10: 0000000000000000 R11: 0000000000000001 R12: ffff888084ef0540
R13: ffff88800011aa80 R14: ffff888084ef0558 R15: 0000000000000000
 refcount_add include/linux/refcount.h:204 [inline]
 refcount_inc include/linux/refcount.h:241 [inline]
 sock_hold include/net/sock.h:692 [inline]
 smc_release+0x41d/0x490 net/smc/af_smc.c:180
 __sock_release+0xcd/0x280 net/socket.c:596
 sock_close+0x18/0x20 net/socket.c:1277
 __fput+0x285/0x920 fs/file_table.c:281
 task_work_run+0xdd/0x190 kernel/task_work.c:141
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:140 [inline]
 exit_to_user_mode_prepare+0x195/0x1c0 kernel/entry/common.c:167
 syscall_exit_to_user_mode+0x59/0x2b0 kernel/entry/common.c:242
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x416f01
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 1b 00 00 c3 48 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:000000000169fbe0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000005 RCX: 0000000000416f01
RDX: 0000000000000000 RSI: 000000000000097b RDI: 0000000000000004
RBP: 0000000000000001 R08: 0000000000d9297a R09: 0000000000d9297e
R10: 000000000169fcd0 R11: 0000000000000293 R12: 000000000118d940
R13: 000000000118d940 R14: ffffffffffffffff R15: 000000000118cfec
Kernel Offset: disabled
Rebooting in 86400 seconds..

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