As per the comment in include/linux/net.h, the recvfrom handlers
should expect msg_name to be NULL. However, bt_sock_recvmsg()
is currently not checking it, which could lead to a NULL pointer
dereference.
The following NULL pointer dereference was produced while testing
L2CAP datagram reception. Note that the kernel is tainted due to
the r8723bs module being inserted. However, it seems the fix still
applies.