[syzbot] [bluetooth?] possible deadlock in hci_rfkill_set_block

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ce55c22ec8b2 Merge tag 'net-6.6-rc7' of git://git.kernel.o..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=17645b9d680000
kernel config: https://syzkaller.appspot.com/x/.config?x=849fe52ba7c6d78a
dashboard link: https://syzkaller.appspot.com/bug?extid=f93d183bc91522d90de9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15bcf805680000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1122c7b1680000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f6762ae43666/disk-ce55c22e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9b2c191a2c66/vmlinux-ce55c22e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/931e7d3d48a1/bzImage-ce55c22e.xz

The issue was bisected to:

commit 92d4abd66f7080075793970fc8f241239e58a9e7
Author: Arkadiusz Bokowy <arkadius...@gmail.com>
Date: Wed Sep 20 15:30:07 2023 +0000

Bluetooth: vhci: Fix race when opening vhci device

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=107ea899680000
final oops: https://syzkaller.appspot.com/x/report.txt?x=127ea899680000
console output: https://syzkaller.appspot.com/x/log.txt?x=147ea899680000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f93d18...@syzkaller.appspotmail.com
Fixes: 92d4abd66f70 ("Bluetooth: vhci: Fix race when opening vhci device")

======================================================
WARNING: possible circular locking dependency detected
6.6.0-rc6-syzkaller-00182-gce55c22ec8b2 #0 Not tainted
------------------------------------------------------
syz-executor269/5035 is trying to acquire lock:
ffff8880737b4dc0 ((work_completion)(&hdev->tx_work)){+.+.}-{0:0}, at: __flush_work+0xe9/0xac0 kernel/workqueue.c:3403

but task is already holding lock:
ffff8880737b50b8 (&hdev->req_lock){+.+.}-{3:3}, at: hci_dev_do_close net/bluetooth/hci_core.c:552 [inline]
ffff8880737b50b8 (&hdev->req_lock){+.+.}-{3:3}, at: hci_rfkill_set_block+0x12d/0x210 net/bluetooth/hci_core.c:956

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&hdev->req_lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x136/0xd60 kernel/locking/mutex.c:747
hci_dev_do_close net/bluetooth/hci_core.c:552 [inline]
hci_rfkill_set_block+0x12d/0x210 net/bluetooth/hci_core.c:956
rfkill_set_block+0x1e7/0x430 net/rfkill/core.c:346
rfkill_fop_write+0x5bb/0x790 net/rfkill/core.c:1305
vfs_write+0x286/0xaf0 fs/read_write.c:582
ksys_write+0x1a0/0x2c0 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #2 (rfkill_global_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x136/0xd60 kernel/locking/mutex.c:747
rfkill_register+0x34/0x8c0 net/rfkill/core.c:1075
hci_register_dev+0x4e3/0xa40 net/bluetooth/hci_core.c:2656
__vhci_create_device drivers/bluetooth/hci_vhci.c:437 [inline]
vhci_create_device+0x3ba/0x720 drivers/bluetooth/hci_vhci.c:478
vhci_get_user drivers/bluetooth/hci_vhci.c:535 [inline]
vhci_write+0x3c7/0x480 drivers/bluetooth/hci_vhci.c:615
call_write_iter include/linux/fs.h:1956 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x782/0xaf0 fs/read_write.c:584
ksys_write+0x1a0/0x2c0 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #1 (&data->open_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x136/0xd60 kernel/locking/mutex.c:747
vhci_send_frame+0x8e/0xf0 drivers/bluetooth/hci_vhci.c:78
hci_send_frame+0x1ef/0x370 net/bluetooth/hci_core.c:3039
hci_sched_acl_pkt net/bluetooth/hci_core.c:3651 [inline]
hci_sched_acl net/bluetooth/hci_core.c:3736 [inline]
hci_tx_work+0xed4/0x1ef0 net/bluetooth/hci_core.c:3835
process_one_work kernel/workqueue.c:2630 [inline]
process_scheduled_works+0x90f/0x1400 kernel/workqueue.c:2703
worker_thread+0xa5f/0xff0 kernel/workqueue.c:2784
kthread+0x2d3/0x370 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304

-> #0 ((work_completion)(&hdev->tx_work)){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3868 [inline]
__lock_acquire+0x39ff/0x7f70 kernel/locking/lockdep.c:5136
lock_acquire+0x1e3/0x520 kernel/locking/lockdep.c:5753
__flush_work+0x102/0xac0 kernel/workqueue.c:3403
hci_dev_close_sync+0x237/0xfe0 net/bluetooth/hci_sync.c:4982
hci_dev_do_close net/bluetooth/hci_core.c:554 [inline]
hci_rfkill_set_block+0x135/0x210 net/bluetooth/hci_core.c:956
rfkill_set_block+0x1e7/0x430 net/rfkill/core.c:346
rfkill_fop_write+0x5bb/0x790 net/rfkill/core.c:1305
vfs_write+0x286/0xaf0 fs/read_write.c:582
ksys_write+0x1a0/0x2c0 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

other info that might help us debug this:

Chain exists of:
(work_completion)(&hdev->tx_work) --> rfkill_global_mutex --> &hdev->req_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&hdev->req_lock);
lock(rfkill_global_mutex);
lock(&hdev->req_lock);
lock((work_completion)(&hdev->tx_work));

*** DEADLOCK ***

2 locks held by syz-executor269/5035:
#0: ffffffff8e794ea8 (rfkill_global_mutex){+.+.}-{3:3}, at: rfkill_fop_write+0x1a9/0x790 net/rfkill/core.c:1297
#1: ffff8880737b50b8 (&hdev->req_lock){+.+.}-{3:3}, at: hci_dev_do_close net/bluetooth/hci_core.c:552 [inline]
#1: ffff8880737b50b8 (&hdev->req_lock){+.+.}-{3:3}, at: hci_rfkill_set_block+0x12d/0x210 net/bluetooth/hci_core.c:956

stack backtrace:
CPU: 1 PID: 5035 Comm: syz-executor269 Not tainted 6.6.0-rc6-syzkaller-00182-gce55c22ec8b2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
check_noncircular+0x375/0x4a0 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3868 [inline]
__lock_acquire+0x39ff/0x7f70 kernel/locking/lockdep.c:5136
lock_acquire+0x1e3/0x520 kernel/locking/lockdep.c:5753
__flush_work+0x102/0xac0 kernel/workqueue.c:3403
hci_dev_close_sync+0x237/0xfe0 net/bluetooth/hci_sync.c:4982
hci_dev_do_close net/bluetooth/hci_core.c:554 [inline]
hci_rfkill_set_block+0x135/0x210 net/bluetooth/hci_core.c:956
rfkill_set_block+0x1e7/0x430 net/rfkill/core.c:346
rfkill_fop_write+0x5bb/0x790 net/rfkill/core.c:1305
vfs_write+0x286/0xaf0 fs/read_write.c:582
ksys_write+0x1a0/0x2c0 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f3ba6729479
Code: 48 83 c4 28 c3 e8 e7 18 00 00 0f 1f 80 00 00 00 00 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc064fec88 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f3ba6780043 RCX: 00007f3ba6729479
RDX: 0000000000000008 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 00007ffc064fecd0 R08: 000000ff00fff650 R09: 000000ff00fff650
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc064fecb8
R13: 00007f3ba67ad5b0 R14: 0000000000000000 R15: 0000000000000001
</TASK>


---
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If the bug is already fixed, let syzbot know by replying with:
#syz fix: exact-commit-title

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#syz test: git://repo/address.git branch-or-commit-hash
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#syz undup

[Hillf Danton]

On Mon, 23 Oct 2023 17:01:07 -0700

> HEAD commit: ce55c22ec8b2 Merge tag 'net-6.6-rc7' of git://git.kernel.o..
> git tree: upstream

> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1122c7b1680000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

--- x/drivers/bluetooth/hci_vhci.c
+++ y/drivers/bluetooth/hci_vhci.c
@@ -74,11 +74,7 @@ static int vhci_send_frame(struct hci_de
struct vhci_data *data = hci_get_drvdata(hdev);

memcpy(skb_push(skb, 1), &hci_skb_pkt_type(skb), 1);
-
- mutex_lock(&data->open_mutex);
skb_queue_tail(&data->readq, skb);
- mutex_unlock(&data->open_mutex);
-
wake_up_interruptible(&data->read_wait);
return 0;
}
@@ -464,7 +460,7 @@ static int __vhci_create_device(struct v
skb_put_u8(skb, 0xff);
skb_put_u8(skb, opcode);
put_unaligned_le16(hdev->id, skb_put(skb, 2));
- skb_queue_tail(&data->readq, skb);
+ skb_queue_head(&data->readq, skb);

wake_up_interruptible(&data->read_wait);
return 0;
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+f93d18...@syzkaller.appspotmail.com

Tested on:

commit: d88520ad Merge tag 'pull-nfsd-fix' of git://git.kernel..
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=159aaf83680000
kernel config: https://syzkaller.appspot.com/x/.config?x=84ec698011085fee

dashboard link: https://syzkaller.appspot.com/bug?extid=f93d183bc91522d90de9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=13ed6f33680000

Note: testing is done by a robot and is best-effort only.

[Fedor Pchelkin]

Was fixed by 769bf60e17ee ("Bluetooth: Fix deadlock in vhci_send_frame").

#syz fix: Bluetooth: Fix deadlock in vhci_send_frame