[PATCH v2] Bluetooth: hci_core: fix suspicious RCU usage in hci_conn_drop()

[Yunseong Kim]

Protection from the queuing operation is achieved with an RCU read lock
to avoid calling 'queue_delayed_work()' after 'cancel_delayed_work()',
but this does not apply to 'hci_conn_drop()'.

commit deee93d13d38 ("Bluetooth: use hdev->workqueue when queuing
 hdev->{cmd,ncmd}_timer works")

The situation described raises concerns about suspicious RCU usage in a
corrupted context.

CPU 1                   CPU 2
 hci_dev_do_reset()
  synchronize_rcu()      hci_conn_drop()
  drain_workqueue()       <-- no RCU read protection during queuing. -->
                           queue_delayed_work()

It displays a warning message like the following

Bluetooth: hci0: unexpected cc 0x0c38 length: 249 > 2
=============================
WARNING: suspicious RCU usage
6.10.0-rc6-01340-gf14c0bb78769 #5 Not tainted
-----------------------------
net/mac80211/util.c:4000 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
2 locks held by syz-executor/798:
 #0: ffff800089a3de50 (rtnl_mutex){+.+.}-{4:4},
    at: rtnl_lock+0x28/0x40 net/core/rtnetlink.c:79

stack backtrace:
CPU: 0 PID: 798 Comm: syz-executor Not tainted
  6.10.0-rc6-01340-gf14c0bb78769 #5
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace.part.0+0x1b8/0x1d0 arch/arm64/kernel/stacktrace.c:317
 dump_backtrace arch/arm64/kernel/stacktrace.c:323 [inline]
 show_stack+0x34/0x50 arch/arm64/kernel/stacktrace.c:324
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xf0/0x170 lib/dump_stack.c:114
 dump_stack+0x20/0x30 lib/dump_stack.c:123
 lockdep_rcu_suspicious+0x204/0x2f8 kernel/locking/lockdep.c:6712
 ieee80211_check_combinations+0x71c/0x828 [mac80211]
 ieee80211_check_concurrent_iface+0x494/0x700 [mac80211]
 ieee80211_open+0x140/0x238 [mac80211]
 __dev_open+0x270/0x498 net/core/dev.c:1474
 __dev_change_flags+0x47c/0x610 net/core/dev.c:8837
 dev_change_flags+0x98/0x170 net/core/dev.c:8909
 devinet_ioctl+0xdf0/0x18d0 net/ipv4/devinet.c:1177
 inet_ioctl+0x34c/0x388 net/ipv4/af_inet.c:1003
 sock_do_ioctl+0xe4/0x240 net/socket.c:1222
 sock_ioctl+0x4cc/0x740 net/socket.c:1341
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl fs/ioctl.c:893 [inline]
 __arm64_sys_ioctl+0x184/0x218 fs/ioctl.c:893
 __invoke_syscall arch/arm64/kernel/syscall.c:34 [inline]
 invoke_syscall+0x90/0x2e8 arch/arm64/kernel/syscall.c:48
 el0_svc_common.constprop.0+0x200/0x2a8 arch/arm64/kernel/syscall.c:131
 el0_svc+0x48/0xc0 arch/arm64/kernel/entry-common.c:712
 el0t_64_sync_handler+0x120/0x130 arch/arm64/kernel/entry-common.c:730
 el0t_64_sync+0x190/0x198 arch/arm64/kernel/entry.S:598

This patch attempts to fix that issue with the same convention.

Cc: stable@xxxxxxxxxxxxxxx # v6.1+
Fixes: deee93d13d38 ("Bluetooth: use hdev->workqueue when queuing hdev->{cmd,ncmd}_timer works")
Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
Tested-by: Yunseong Kim <yskelg@xxxxxxxxx>
Signed-off-by: Yunseong Kim <yskelg@xxxxxxxxx>
---
 include/net/bluetooth/hci_core.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index 31020891fc68..111509dc1a23 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -1572,8 +1572,13 @@ static inline void hci_conn_drop(struct hci_conn *conn)
 		}
 
 		cancel_delayed_work(&conn->disc_work);
-		queue_delayed_work(conn->hdev->workqueue,
-				   &conn->disc_work, timeo);
+
+		rcu_read_lock();
+		if (!hci_dev_test_flag(conn->hdev, HCI_CMD_DRAIN_WORKQUEUE)) {
+			queue_delayed_work(conn->hdev->workqueue,
+							   &conn->disc_work, timeo);
+		}
+		rcu_read_unlock();
 	}
 }
 
-- 
2.45.2