Re: [syzbot] [bluetooth?] possible deadlock in rfcomm_dlc_exists

From: syzbot
Date: Fri Mar 31 2023 - 04:16:39 EST

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in rfcomm_dev_ioctl

======================================================
WARNING: possible circular locking dependency detected
6.3.0-rc4-next-20230330-syzkaller-dirty #0 Not tainted
------------------------------------------------------
syz-executor.0/5603 is trying to acquire lock:
ffff88801e179130 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1697 [inline]
ffff88801e179130 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: __rfcomm_create_dev net/bluetooth/rfcomm/tty.c:417 [inline]
ffff88801e179130 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: rfcomm_create_dev net/bluetooth/rfcomm/tty.c:488 [inline]
ffff88801e179130 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: rfcomm_dev_ioctl+0x9ca/0x1cb0 net/bluetooth/rfcomm/tty.c:590

but task is already holding lock:
ffffffff8e35cc88 (rfcomm_ioctl_mutex){+.+.}-{3:3}, at: rfcomm_create_dev net/bluetooth/rfcomm/tty.c:487 [inline]
ffffffff8e35cc88 (rfcomm_ioctl_mutex){+.+.}-{3:3}, at: rfcomm_dev_ioctl+0x8a2/0x1cb0 net/bluetooth/rfcomm/tty.c:590

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (rfcomm_ioctl_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x12f/0x1350 kernel/locking/mutex.c:747
rfcomm_create_dev net/bluetooth/rfcomm/tty.c:487 [inline]
rfcomm_dev_ioctl+0x8a2/0x1cb0 net/bluetooth/rfcomm/tty.c:590
rfcomm_sock_ioctl+0xb7/0xe0 net/bluetooth/rfcomm/sock.c:880
sock_do_ioctl+0xcc/0x230 net/socket.c:1199
sock_ioctl+0x1f8/0x680 net/socket.c:1316
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+0x197/0x210 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3108 [inline]
check_prevs_add kernel/locking/lockdep.c:3227 [inline]
validate_chain kernel/locking/lockdep.c:3842 [inline]
__lock_acquire+0x2f21/0x5df0 kernel/locking/lockdep.c:5074
lock_acquire.part.0+0x11c/0x370 kernel/locking/lockdep.c:5691
lock_sock_nested+0x3a/0xf0 net/core/sock.c:3474
lock_sock include/net/sock.h:1697 [inline]
__rfcomm_create_dev net/bluetooth/rfcomm/tty.c:417 [inline]
rfcomm_create_dev net/bluetooth/rfcomm/tty.c:488 [inline]
rfcomm_dev_ioctl+0x9ca/0x1cb0 net/bluetooth/rfcomm/tty.c:590
rfcomm_sock_ioctl+0xb7/0xe0 net/bluetooth/rfcomm/sock.c:880
sock_do_ioctl+0xcc/0x230 net/socket.c:1199
sock_ioctl+0x1f8/0x680 net/socket.c:1316
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+0x197/0x210 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(rfcomm_ioctl_mutex);
lock(sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM);
lock(rfcomm_ioctl_mutex);
lock(sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM);

*** DEADLOCK ***

1 lock held by syz-executor.0/5603:
#0: ffffffff8e35cc88 (rfcomm_ioctl_mutex){+.+.}-{3:3}, at: rfcomm_create_dev net/bluetooth/rfcomm/tty.c:487 [inline]
#0: ffffffff8e35cc88 (rfcomm_ioctl_mutex){+.+.}-{3:3}, at: rfcomm_dev_ioctl+0x8a2/0x1cb0 net/bluetooth/rfcomm/tty.c:590

stack backtrace:
CPU: 0 PID: 5603 Comm: syz-executor.0 Not tainted 6.3.0-rc4-next-20230330-syzkaller-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2188
check_prev_add kernel/locking/lockdep.c:3108 [inline]
check_prevs_add kernel/locking/lockdep.c:3227 [inline]
validate_chain kernel/locking/lockdep.c:3842 [inline]
__lock_acquire+0x2f21/0x5df0 kernel/locking/lockdep.c:5074
lock_acquire.part.0+0x11c/0x370 kernel/locking/lockdep.c:5691
lock_sock_nested+0x3a/0xf0 net/core/sock.c:3474
lock_sock include/net/sock.h:1697 [inline]
__rfcomm_create_dev net/bluetooth/rfcomm/tty.c:417 [inline]
rfcomm_create_dev net/bluetooth/rfcomm/tty.c:488 [inline]
rfcomm_dev_ioctl+0x9ca/0x1cb0 net/bluetooth/rfcomm/tty.c:590
rfcomm_sock_ioctl+0xb7/0xe0 net/bluetooth/rfcomm/sock.c:880
sock_do_ioctl+0xcc/0x230 net/socket.c:1199
sock_ioctl+0x1f8/0x680 net/socket.c:1316
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+0x197/0x210 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f94d848c0f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f94d911c168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f94d85ac050 RCX: 00007f94d848c0f9
RDX: 0000000020000100 RSI: 00000000400452c8 RDI: 0000000000000006
RBP: 00007f94d84e7b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffef88f28bf R14: 00007f94d911c300 R15: 0000000000022000
</TASK>


Tested on:

commit: a6d9e303 Add linux-next specific files for 20230330
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14b657d5c80000
kernel config: https://syzkaller.appspot.com/x/.config?x=aceb117f7924508e
dashboard link: https://syzkaller.appspot.com/bug?extid=b69a625d06e8ece26415
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch: https://syzkaller.appspot.com/x/patch.diff?x=1741d1cdc80000