Bug 217383

Our static analysis tool finds a possible data race in the l2cap protocol
in Linux 6.3.0-rc7:

In most calling contexts, the variable sk->sk_socket is accessed
with holding the lock sk->sk_callback_lock. Here is an example:

  l2cap_sock_accept() --> Line 346 in net/bluetooth/l2cap_sock.c
      bt_accept_dequeue() --> Line 368 in net/bluetooth/l2cap_sock.c
          sock_graft() --> Line 240 in net/bluetooth/af_bluetooth.c
              write_lock_bh(&sk->sk_callback_lock); --> Line 2081 in include/net/sock.h (Lock sk->sk_callback_lock)
              sk_set_socket() --> Line 2084 in include/net/sock.h
                  sk->sk_socket = sock; --> Line 2054 in include/net/sock.h (Access sk->sk_socket)

However, in the following calling context:
 
  sco_sock_shutdown() --> Line 1227 in net/bluetooth/sco.c
      __sco_sock_close() --> Line 1243 in net/bluetooth/sco.c
          BT_DBG(..., sk->sk_socket); --> Line 431 in net/bluetooth/sco.c (Access sk->sk_socket)

the variable sk->sk_socket is accessed without holding the lock
sk->sk_callback_lock, and thus a data race may occur.

Reported-by: BassCheck <bass@buaa.edu.cn>