general protection fault in rfcomm_dlc_open

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    cd86972a Merge branch 'tcp-undo-congestion'
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=127331dca00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=429a5a550a968ac7
dashboard link: https://syzkaller.appspot.com/bug?extid=7cd22aae14e82bcf8379
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+7cd22aae14e82bcf8379@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: 31668 Comm: syz-executor.5 Not tainted 5.1.0-rc6+ #163
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:rfcomm_dlc_get net/bluetooth/rfcomm/core.c:360 [inline]
RIP: 0010:__rfcomm_dlc_open net/bluetooth/rfcomm/core.c:396 [inline]
RIP: 0010:rfcomm_dlc_open+0x28a/0xd60 net/bluetooth/rfcomm/core.c:431
Code: 9d 50 ff ff ff 74 67 e8 14 b6 16 fb 48 8d bb 44 01 00 00 48 b9 00 00  
00 00 00 fc ff df 48 89 f8 48 89 fa 48 c1 e8 03 83 e2 07 <0f> b6 04 08 38  
d0 7f 08 84 c0 0f 85 e6 09 00 00 0f b6 b3 44 01 00
RSP: 0018:ffff888068067c88 EFLAGS: 00010206
RAX: 0620fbe76423b6ea RBX: 3107df3b211db60f RCX: dffffc0000000000
RDX: 0000000000000003 RSI: ffffffff8659d70c RDI: 3107df3b211db753
RBP: ffff888068067d60 R08: ffff8880a7f1e3c0 R09: fffffbfff12898a5
R10: ffff888068067c78 R11: ffffffff8944c527 R12: ffff888085e7f0c0
R13: ffff88809b3b2300 R14: 1ffff1100d00cf97 R15: 000000008659d603
FS:  00007f9e3b56f700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000073c000 CR3: 000000006895d000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 rfcomm_sock_connect+0x38a/0x4b0 net/bluetooth/rfcomm/sock.c:416
 __sys_connect+0x266/0x330 net/socket.c:1828
 __do_sys_connect net/socket.c:1839 [inline]
 __se_sys_connect net/socket.c:1836 [inline]
 __x64_sys_connect+0x73/0xb0 net/socket.c:1836
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x458da9
Code: ad b8 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 b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f9e3b56ec78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458da9
RDX: 000000000000000e RSI: 0000000020000080 RDI: 0000000000000004
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9e3b56f6d4
R13: 00000000004bf18a R14: 00000000004d0218 R15: 00000000ffffffff
Modules linked in:
---[ end trace cac206debc49dd35 ]---
RIP: 0010:rfcomm_dlc_get net/bluetooth/rfcomm/core.c:360 [inline]
RIP: 0010:__rfcomm_dlc_open net/bluetooth/rfcomm/core.c:396 [inline]
RIP: 0010:rfcomm_dlc_open+0x28a/0xd60 net/bluetooth/rfcomm/core.c:431
Code: 9d 50 ff ff ff 74 67 e8 14 b6 16 fb 48 8d bb 44 01 00 00 48 b9 00 00  
00 00 00 fc ff df 48 89 f8 48 89 fa 48 c1 e8 03 83 e2 07 <0f> b6 04 08 38  
d0 7f 08 84 c0 0f 85 e6 09 00 00 0f b6 b3 44 01 00
RSP: 0018:ffff888068067c88 EFLAGS: 00010206
RAX: 0620fbe76423b6ea RBX: 3107df3b211db60f RCX: dffffc0000000000
RDX: 0000000000000003 RSI: ffffffff8659d70c RDI: 3107df3b211db753
RBP: ffff888068067d60 R08: ffff8880a7f1e3c0 R09: fffffbfff12898a5
R10: ffff888068067c78 R11: ffffffff8944c527 R12: ffff888085e7f0c0
R13: ffff88809b3b2300 R14: 1ffff1100d00cf97 R15: 000000008659d603
FS:  00007f9e3b56f700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000006895d000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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