* [syzbot] [bluetooth?] possible deadlock in l2cap_chan_connect (2)
@ 2026-10-06 16:19 syzbot
2026-10-07 4:49 ` Hillf Danton
0 siblings, 1 reply; 2+ messages in thread
From: syzbot @ 2026-10-06 16:19 UTC (permalink / raw)
To: linux-bluetooth, linux-kernel, luiz.dentz, marcel, syzkaller-bugs
Hello,
syzbot found the following issue on:
HEAD commit: 2c3418fffa9d Merge tag 'keys-v7.3-rc7' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ca6ff5580000
kernel config: https://syzkaller.appspot.com/x/.config?x=929e4854a828f434
dashboard link: https://syzkaller.appspot.com/bug?extid=1fed874be1d7e459b5a3
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101e6f25580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13cfbff5580000
Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-2c3418ff.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1818dc9d2f44/vmlinux-2c3418ff.xz
kernel image: https://storage.googleapis.com/syzbot-assets/52ad1b5b053d/bzImage-2c3418ff.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1fed874be1d7e459b5a3@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/5921 is trying to acquire lock:
ffff88802d8700b8 (&hdev->lock){+.+.}-{4:4}, at: l2cap_chan_connect+0xac/0x2110 net/bluetooth/l2cap_core.c:7289
but task is already holding lock:
ffffffff90f83f60 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_dlc_open+0x92/0xac0 net/bluetooth/rfcomm/core.c:426
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (rfcomm_mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
rfcomm_security_cfm+0x3f/0x4b0 net/bluetooth/rfcomm/core.c:2223
hci_auth_cfm include/net/bluetooth/hci_core.h:2203 [inline]
hci_auth_complete_evt+0x811/0x1180 net/bluetooth/hci_event.c:3554
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:4087
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
process_scheduled_works kernel/workqueue.c:3479 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
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 (hci_cb_list_lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
hci_connect_cfm include/net/bluetooth/hci_core.h:2164 [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:4087
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
process_scheduled_works kernel/workqueue.c:3479 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
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
-> #0 (&hdev->lock){+.+.}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
l2cap_chan_connect+0xac/0x2110 net/bluetooth/l2cap_core.c:7289
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:419
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
other info that might help us debug this:
Chain exists of:
&hdev->lock --> hci_cb_list_lock --> rfcomm_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(rfcomm_mutex);
lock(hci_cb_list_lock);
lock(rfcomm_mutex);
lock(&hdev->lock);
*** DEADLOCK ***
locks held by syz.0.17/5921: 1, last CPU#3:
#0: ffffffff90f83f60 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_dlc_open+0x92/0xac0 net/bluetooth/rfcomm/core.c:426
stack backtrace:
CPU: 3 UID: 0 PID: 5921 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
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:2087
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
l2cap_chan_connect+0xac/0x2110 net/bluetooth/l2cap_core.c:7289
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:419
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
RIP: 0033:0x7fa5d1b9e199
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc664cdb68 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007fa5d1e25fa0 RCX: 00007fa5d1b9e199
RDX: 000000000000000a RSI: 0000200000000040 RDI: 0000000000000004
RBP: 00007fa5d1c358e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa5d1e25fac R14: 00007fa5d1e25fa0 R15: 00007fa5d1e25fa0
</TASK>
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot will keep track of this issue. See:
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If the report is already addressed, let syzbot know by replying with:
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If you want syzbot to run the reproducer, reply with:
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If you want to overwrite report's subsystems, reply with:
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If you want to undo deduplication, reply with:
#syz undup
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [syzbot] [bluetooth?] possible deadlock in l2cap_chan_connect (2)
2026-10-06 16:19 [syzbot] [bluetooth?] possible deadlock in l2cap_chan_connect (2) syzbot
@ 2026-10-07 4:49 ` Hillf Danton
0 siblings, 0 replies; 2+ messages in thread
From: Hillf Danton @ 2026-10-07 4:49 UTC (permalink / raw)
To: syzbot; +Cc: linux-kernel, syzkaller-bugs
> Date: Tue, 06 Oct 2026 09:19:25 -0700
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 2c3418fffa9d Merge tag 'keys-v7.3-rc7' of git://git.kernel..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17ca6ff5580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=929e4854a828f434
> dashboard link: https://syzkaller.appspot.com/bug?extid=1fed874be1d7e459b5a3
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101e6f25580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13cfbff5580000
#syz test
--- x/net/bluetooth/rfcomm/core.c
+++ y/net/bluetooth/rfcomm/core.c
@@ -42,6 +42,7 @@ static int channel_mtu = -1;
static struct task_struct *rfcomm_thread;
+static DEFINE_MUTEX(rfcomm_cb_mutex);
static DEFINE_MUTEX(rfcomm_mutex);
#define rfcomm_lock() mutex_lock(&rfcomm_mutex)
#define rfcomm_unlock() mutex_unlock(&rfcomm_mutex)
@@ -701,7 +702,9 @@ static struct rfcomm_session *rfcomm_ses
return NULL;
}
+ mutex_lock(&rfcomm_cb_mutex);
list_add(&s->list, &session_list);
+ mutex_unlock(&rfcomm_cb_mutex);
return s;
}
@@ -743,6 +746,7 @@ static struct rfcomm_session *rfcomm_ses
{
struct rfcomm_dlc *d, *n;
+ mutex_lock(&rfcomm_cb_mutex);
s->state = BT_CLOSED;
BT_DBG("session %p state %ld err %d", s, s->state, err);
@@ -754,7 +758,9 @@ static struct rfcomm_session *rfcomm_ses
}
rfcomm_session_clear_timer(s);
- return rfcomm_session_del(s);
+ s = rfcomm_session_del(s);
+ mutex_unlock(&rfcomm_cb_mutex);
+ return s;
}
static struct rfcomm_session *rfcomm_session_create(bdaddr_t *src,
@@ -2220,11 +2226,11 @@ static void rfcomm_security_cfm(struct h
BT_DBG("conn %p status 0x%02x encrypt 0x%02x", conn, status, encrypt);
- rfcomm_lock();
+ mutex_lock(&rfcomm_cb_mutex);
s = rfcomm_session_get(&conn->hdev->bdaddr, &conn->dst);
if (!s) {
- rfcomm_unlock();
+ mutex_unlock(&rfcomm_cb_mutex);
return;
}
@@ -2258,7 +2264,7 @@ static void rfcomm_security_cfm(struct h
set_bit(RFCOMM_AUTH_REJECT, &d->flags);
}
- rfcomm_unlock();
+ mutex_unlock(&rfcomm_cb_mutex);
rfcomm_schedule();
}
--
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-10-07 4:52 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
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2026-10-06 16:19 [syzbot] [bluetooth?] possible deadlock in l2cap_chan_connect (2) syzbot
2026-10-07 4:49 ` Hillf Danton
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