BUG: general protection fault in hci_uart_tty_ioctl

[Yu Hao]

Hello,

We found the following issue using syzkaller on Linux v6.2.0.

In function `hci_uart_tty_ioctl`, there is a race condition
between HCIUARTSETPROTO and HCIUARTGETPROTO.
HCI_UART_PROTO_SET is set before `hu->proto` is set.
Thus it may dereference a null pointer.

The full report including the Syzkaller reproducer & C reproducer:
https://gist.github.com/ZHYfeng/a3e3ff2bdfea5ed5de5475f0b54d55cb

The brief report is below:

Syzkaller hit 'general protection fault in hci_uart_tty_ioctl' bug.

general protection fault, probably for non-canonical address
0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 PID: 8770 Comm: syz-executor.0 Not tainted 6.2.0 #4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:hci_uart_tty_ioctl+0x244/0xc20 drivers/bluetooth/hci_ldisc.c:774
Code: df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 cf 08 00 00 48 8b 9b
b8 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 <0f> b6
04 02 84 c0 74 08 3c 03 0f 8e 5f 08 00 00 44 8b 23 e9 14 ff
RSP: 0018:ffffc900022a7d10 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff8710057c
RDX: 0000000000000000 RSI: ffff888046df8000 RDI: ffff88801cf510b8
RBP: 0000000000000001 R08: 0000000000000001 R09: ffffed10039ea204
R10: ffff88801cf5101f R11: ffffed10039ea203 R12: ffff8880204eb000
R13: 0000000000000000 R14: ffffffffffffffe7 R15: 00000000800401c0
FS:  00007f203e7dd700(0000) GS:ffff88802ca00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005587ec7f32d8 CR3: 000000004629e000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 tty_ioctl+0xac0/0x1420 drivers/tty/tty_io.c:2784
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x198/0x210 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f203f0902fd
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f203e7dcc58 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f203f1bc020 RCX: 00007f203f0902fd
RDX: 0000000000000000 RSI: 00000000800455c9 RDI: 0000000000000003
RBP: 00007f203f0fec89 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffee4615aef R14: 00007ffee4615ca0 R15: 00007f203e7dcdc0
 </TASK>