BUG: unable to handle kernel NULL pointer dereference in snd_seq_ioctl

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 6741c4bb389d Merge tag 'mips_fixes_4.17_2' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14dac977800000
kernel config: https://syzkaller.appspot.com/x/.config?x=982e2df1b9e60b02
dashboard link: https://syzkaller.appspot.com/bug?extid=3b76465cd552e6f65af2
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [alsa-...@alsa-project.org danie...@google.com
gre...@linuxfoundation.org kees...@chromium.org
linux-...@vger.kernel.org pe...@perex.cz ti...@suse.com
vi...@zeniv.linux.org.uk]

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+3b7646...@syzkaller.appspotmail.com

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD 1cfd19067 P4D 1cfd19067 PUD 1c83be067 PMD 0
Oops: 0002 [#1] SMP KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 16973 Comm: syz-executor7 Not tainted 4.17.0-rc6+ #62
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:_copy_from_user+0x100/0x150 lib/usercopy.c:12
RSP: 0018:ffff88018554fa80 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 00000000000000a8 RCX: ffffffff83538c60
RDX: 0000000000000001 RSI: 00000000000000a8 RDI: ffff88018554fb00
RBP: ffff88018554fab0 R08: ffffed0030aa9f75 R09: ffffed0030aa9f75
R10: ffffed0030aa9f74 R11: ffff88018554fba7 R12: 0000000020418ff8
R13: 0000000020418f50 R14: ffff88018554fb00 R15: 00007ffffffff000
FS: 00007fd068bdb700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000001d95ca000 CR4: 00000000001426f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
copy_from_user include/linux/uaccess.h:147 [inline]
snd_seq_ioctl+0x1e8/0x440 sound/core/seq/seq_clientmgr.c:2139
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
__do_sys_ioctl fs/ioctl.c:708 [inline]
__se_sys_ioctl fs/ioctl.c:706 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455a09
RSP: 002b:00007fd068bdac68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd068bdb6d4 RCX: 0000000000455a09
RDX: 0000000020418f50 RSI: 00000000c0a85320 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 000000000000030a R14: 00000000006f8990 R15: 0000000000000000
Code: 4d 85 e4 75 38 e8 e1 a3 25 fe 4c 89 e0 48 83 c4 08 5b 41 5c 41 5d 41
5e 41 5f 5d c3 e8 ca a3 25 fe 89 de 4c 89 f7 e8 c0 00 62 fe <00> 00 00 00
00 00 00 00 e8 83 0c 19 04 41 89 c4 eb b4 e8 a9 a3
RIP: _copy_from_user+0x100/0x150 lib/usercopy.c:12 RSP: ffff88018554fa80
CR2: 0000000000000000
---[ end trace 0a627160c7d4eb3e ]---


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.