general protection fault in snd_timer_open

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    6980b7f6 Add linux-next specific files for 20191111
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=149fae72e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2af7db1972ec750e
dashboard link: https://syzkaller.appspot.com/bug?extid=7a0ab45b9c1dc81c9e6b
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7a0ab45b9c1dc81c9e6b@xxxxxxxxxxxxxxxxxxxxxxxxx

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 26749 Comm: syz-executor.4 Not tainted 5.4.0-rc6-next-20191111  
#0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:snd_timer_check_master sound/core/timer.c:228 [inline]
RIP: 0010:snd_timer_open+0x943/0x1150 sound/core/timer.c:326
Code: 48 89 85 58 ff ff ff 4c 89 f0 48 c1 e8 03 4c 01 e8 48 89 85 50 ff ff  
ff eb 36 e8 38 1e ee fb 48 8d 7b 78 48 89 f8 48 c1 e8 03 <42> 80 3c 28 00  
0f 85 f4 05 00 00 48 8b 43 78 49 89 dc 48 83 e8 78
RSP: 0018:ffff888057d978f8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffffffffffff88 RCX: ffffc9000e7ad000
RDX: 0000000000007655 RSI: ffffffff85855cd8 RDI: 0000000000000000
RBP: ffff888057d979c0 R08: ffff8880a180c240 R09: ffff8880a1b0f008
R10: ffffed1014361e08 R11: ffff8880a1b0f047 R12: ffff8880a8f40000
R13: dffffc0000000000 R14: ffff888097688600 R15: ffffffff00000002
FS:  00007f1c13a0a700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000075c000 CR3: 000000009f897000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 snd_seq_timer_open+0x27f/0x590 sound/core/seq/seq_timer.c:281
 queue_use+0xf1/0x270 sound/core/seq/seq_queue.c:489
 snd_seq_queue_alloc+0x2c5/0x4d0 sound/core/seq/seq_queue.c:176
 snd_seq_ioctl_create_queue+0xb0/0x330 sound/core/seq/seq_clientmgr.c:1548
 snd_seq_ioctl+0x21e/0x3e0 sound/core/seq/seq_clientmgr.c:2157
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a219
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f1c13a09c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a219
RDX: 00000000200001c0 RSI: 00000000c08c5332 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1c13a0a6d4
R13: 00000000004ceed0 R14: 00000000004d93d0 R15: 00000000ffffffff
Modules linked in:
---[ end trace fd34b5665372895c ]---
RIP: 0010:snd_timer_check_master sound/core/timer.c:228 [inline]
RIP: 0010:snd_timer_open+0x943/0x1150 sound/core/timer.c:326
Code: 48 89 85 58 ff ff ff 4c 89 f0 48 c1 e8 03 4c 01 e8 48 89 85 50 ff ff  
ff eb 36 e8 38 1e ee fb 48 8d 7b 78 48 89 f8 48 c1 e8 03 <42> 80 3c 28 00  
0f 85 f4 05 00 00 48 8b 43 78 49 89 dc 48 83 e8 78
RSP: 0018:ffff888057d978f8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffffffffffff88 RCX: ffffc9000e7ad000
RDX: 0000000000007655 RSI: ffffffff85855cd8 RDI: 0000000000000000
RBP: ffff888057d979c0 R08: ffff8880a180c240 R09: ffff8880a1b0f008
R10: ffffed1014361e08 R11: ffff8880a1b0f047 R12: ffff8880a8f40000
R13: dffffc0000000000 R14: ffff888097688600 R15: ffffffff00000002
FS:  00007f1c13a0a700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f750abec110 CR3: 000000009f897000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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