Re: [syzbot] INFO: task hung in hci_req_sync

[Pavel Skripkin <paskripkin@gmail.com>]

On 8/12/21 9:13 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    c9194f32bfd9 Merge tag 'ext4_for_linus_stable' of git://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1488f59e300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=343fd21f6f4da2d6
> dashboard link: https://syzkaller.appspot.com/bug?extid=be2baed593ea56c6a84c
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15b5afc6300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15fcd192300000
> 
> Bisection is inconclusive: the issue happens on the oldest tested release.
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17dce4fa300000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=143ce4fa300000
> console output: https://syzkaller.appspot.com/x/log.txt?x=103ce4fa300000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+be2baed593ea56c6a84c@syzkaller.appspotmail.com
> 
> INFO: task syz-executor446:8489 blocked for more than 143 seconds.
>        Not tainted 5.14.0-rc4-syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz-executor446 state:D stack:28712 pid: 8489 ppid:  8452 flags:0x00000000
> Call Trace:
>   context_switch kernel/sched/core.c:4683 [inline]
>   __schedule+0x93a/0x26f0 kernel/sched/core.c:5940
>   schedule+0xd3/0x270 kernel/sched/core.c:6019
>   schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6078
>   __mutex_lock_common kernel/locking/mutex.c:1036 [inline]
>   __mutex_lock+0x7b6/0x10a0 kernel/locking/mutex.c:1104
>   hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
>   hci_inquiry+0x6f4/0x9e0 net/bluetooth/hci_core.c:1357
>   hci_sock_ioctl+0x1a7/0x910 net/bluetooth/hci_sock.c:1060
>   sock_do_ioctl+0xcb/0x2d0 net/socket.c:1094
>   sock_ioctl+0x477/0x6a0 net/socket.c:1221
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:1069 [inline]
>   __se_sys_ioctl fs/ioctl.c:1055 [inline]
>   __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
>   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+0x44/0xae
> RIP: 0033:0x446449
> RSP: 002b:00007f36ab8342e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000004cb400 RCX: 0000000000446449
> RDX: 00000000200000c0 RSI: 00000000800448f0 RDI: 0000000000000004
> RBP: 00000000004cb40c R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000003
> R13: 0000000000000004 R14: 00007f36ab8346b8 R15: 00000000004cb408
> INFO: task syz-executor446:8491 blocked for more than 143 seconds.
>        Not tainted 5.14.0-rc4-syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz-executor446 state:D stack:28176 pid: 8491 ppid:  8452 flags:0x00000004
> Call Trace:
>   context_switch kernel/sched/core.c:4683 [inline]
>   __schedule+0x93a/0x26f0 kernel/sched/core.c:5940
>   schedule+0xd3/0x270 kernel/sched/core.c:6019
>   schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6078
>   __mutex_lock_common kernel/locking/mutex.c:1036 [inline]
>   __mutex_lock+0x7b6/0x10a0 kernel/locking/mutex.c:1104
>   hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
>   hci_inquiry+0x6f4/0x9e0 net/bluetooth/hci_core.c:1357
>   hci_sock_ioctl+0x1a7/0x910 net/bluetooth/hci_sock.c:1060
>   sock_do_ioctl+0xcb/0x2d0 net/socket.c:1094
>   sock_ioctl+0x477/0x6a0 net/socket.c:1221
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:1069 [inline]
>   __se_sys_ioctl fs/ioctl.c:1055 [inline]
>   __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
>   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+0x44/0xae
> RIP: 0033:0x446449
> RSP: 002b:00007f36ab8342e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000004cb400 RCX: 0000000000446449
> RDX: 00000000200000c0 RSI: 00000000800448f0 RDI: 0000000000000004
> RBP: 00000000004cb40c R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
> R13: 0000000000000004 R14: 00007f36ab8346b8 R15: 00000000004cb408
> 
> Showing all locks held in the system:
> 6 locks held by kworker/u4:0/8:
> 1 lock held by khungtaskd/1635:
>   #0: ffffffff8b97c180 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6446
> 1 lock held by in:imklog/8352:
>   #0: ffff888033e1d4f0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:974
> 1 lock held by syz-executor446/8486:
>   #0: ffff8880349c4ff0 (&hdev->req_lock){+.+.}-{3:3}, at: hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
> 1 lock held by syz-executor446/8489:
>   #0: ffff8880349c4ff0 (&hdev->req_lock){+.+.}-{3:3}, at: hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
> 1 lock held by syz-executor446/8491:
>   #0: ffff8880349c4ff0 (&hdev->req_lock){+.+.}-{3:3}, at: hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
> 

Looks like too big timeout is passed from ioctl:


C repro:

     *(uint16_t*)0x200000c0 = 0;
     *(uint16_t*)0x200000c2 = 0;
     memcpy((void*)0x200000c4, "\xf0\x08\xa7", 3);
     *(uint8_t*)0x200000c7 = 0x81;	<- ir.length
     *(uint8_t*)0x200000c8 = 0;
     syscall(__NR_ioctl, r[0], 0x800448f0, 0x200000c0ul);


Then ir.length * msecs_to_jiffies(2000) timeout is passed to
hci_req_sync(). Task will stuck here

	err = wait_event_interruptible_timeout(hdev->req_wait_q,
			hdev->req_status != HCI_REQ_PEND, timeout);

for 258 seconds (I guess, it's because of test environment, but, maybe, 
we should add sanity check for timeout value)



With regards,
Pavel Skripkin