From: syzbot <syzbot+74071deb72339c215b2e@syzkaller.appspotmail.com>
To: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org,
luiz.dentz@gmail.com, marcel@holtmann.org,
syzkaller-bugs@googlegroups.com
Subject: [syzbot] [bluetooth?] possible deadlock in rfcomm_security_cfm
Date: Sat, 29 Aug 2026 08:29:32 -0700 [thread overview]
Message-ID: <6a92fadc.08e933ee.dbf97.008f.GAE@google.com> (raw)
Hello,
syzbot found the following issue on:
HEAD commit: cf72cbb39da8 Merge tag 'io_uring-7.3-20260828' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11b8ae25580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8c5c3949d762a91f
dashboard link: https://syzkaller.appspot.com/bug?extid=74071deb72339c215b2e
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7684a30c51dd/disk-cf72cbb3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4f401bdb1bb3/vmlinux-cf72cbb3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4379cea44543/bzImage-cf72cbb3.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+74071deb72339c215b2e@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
kworker/u9:2/5598 is trying to acquire lock:
ffffffff90f7e040 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_security_cfm+0x3f/0x4b0 net/bluetooth/rfcomm/core.c:2222
but task is already holding lock:
ffffffff90f51500 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_encrypt_cfm+0x11b/0x740 include/net/bluetooth/hci_core.h:2239
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (hci_cb_list_lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5908 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
hci_connect_cfm include/net/bluetooth/hci_core.h:2163 [inline]
hci_remote_features_evt+0x485/0x9b0 net/bluetooth/hci_event.c:3786
hci_event_func net/bluetooth/hci_event.c:7887 [inline]
hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4041
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #1 (&hdev->lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5908 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
l2cap_chan_connect+0xac/0x2050 net/bluetooth/l2cap_core.c:7266
l2cap_sock_connect+0x37a/0x770 net/bluetooth/l2cap_sock.c:255
kernel_connect+0x107/0x160 net/socket.c:3755
rfcomm_session_create net/bluetooth/rfcomm/core.c:808 [inline]
__rfcomm_dlc_open net/bluetooth/rfcomm/core.c:385 [inline]
rfcomm_dlc_open+0x838/0xac0 net/bluetooth/rfcomm/core.c:428
rfcomm_sock_connect+0x42c/0x690 net/bluetooth/rfcomm/sock.c:421
connect_socket net/socket.c:2141 [inline]
connect_socket net/socket.c:2131 [inline]
__sys_connect_file+0x146/0x1a0 net/socket.c:2166
__sys_connect+0x141/0x170 net/socket.c:2183
__do_sys_connect net/socket.c:2189 [inline]
__se_sys_connect net/socket.c:2186 [inline]
__x64_sys_connect+0x72/0xb0 net/socket.c:2186
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (rfcomm_mutex){+.+.}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5254
lock_acquire kernel/locking/lockdep.c:5908 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
rfcomm_security_cfm+0x3f/0x4b0 net/bluetooth/rfcomm/core.c:2222
hci_encrypt_cfm+0x18e/0x740 include/net/bluetooth/hci_core.h:2242
hci_encrypt_change_evt+0x3e1/0xfb0 net/bluetooth/hci_event.c:3715
hci_event_func net/bluetooth/hci_event.c:7887 [inline]
hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4041
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
other info that might help us debug this:
Chain exists of:
rfcomm_mutex --> &hdev->lock --> hci_cb_list_lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(hci_cb_list_lock);
lock(&hdev->lock);
lock(hci_cb_list_lock);
lock(rfcomm_mutex);
*** DEADLOCK ***
locks held by kworker/u9:2/5598: 4, last CPU#0:
#0: ffff88802e39e940 ((wq_completion)hci3#2){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3362
#1: ffffc9000250fd08 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3363
#2: ffff88807d7b80b8 (&hdev->lock){+.+.}-{4:4}, at: hci_encrypt_change_evt+0x83/0xfb0 net/bluetooth/hci_event.c:3627
#3: ffffffff90f51500 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_encrypt_cfm+0x11b/0x740 include/net/bluetooth/hci_core.h:2239
stack backtrace:
CPU: 0 UID: 0 PID: 5598 Comm: kworker/u9:2 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: hci3 hci_rx_work
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2059
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2191
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5254
lock_acquire kernel/locking/lockdep.c:5908 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
rfcomm_security_cfm+0x3f/0x4b0 net/bluetooth/rfcomm/core.c:2222
hci_encrypt_cfm+0x18e/0x740 include/net/bluetooth/hci_core.h:2242
hci_encrypt_change_evt+0x3e1/0xfb0 net/bluetooth/hci_event.c:3715
hci_event_func net/bluetooth/hci_event.c:7887 [inline]
hci_event_packet+0x8e9/0xcd0 net/bluetooth/hci_event.c:7938
hci_rx_work+0x451/0xfc0 net/bluetooth/hci_core.c:4041
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
---
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reply other threads:[~2026-08-29 15:29 UTC|newest]
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