rxrpc: add rxrpc_sock_set_min_security_level

Add a helper to directly set the RXRPC_MIN_SECURITY_LEVEL sockopt from
kernel space without going through a fake uaccess.

Thanks to David Howells for the documentation updates.

Signed-off-by: Christoph Hellwig <[e-mail]>
Acked-by: David Howells <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/rxrpc.rst

···
 	 Encrypted checksum plus packet padded and first eight bytes of packet
 	 encrypted - which includes the actual packet length.
 
-     (c) RXRPC_SECURITY_ENCRYPTED
+     (c) RXRPC_SECURITY_ENCRYPT
 
 	 Encrypted checksum plus entire packet padded and encrypted, including
 	 actual packet length.
···
      This issues a request_key() to get the key representing the security
      context.  The minimum security level can be set::
 
-	unsigned int sec = RXRPC_SECURITY_ENCRYPTED;
+	unsigned int sec = RXRPC_SECURITY_ENCRYPT;
 	setsockopt(client, SOL_RXRPC, RXRPC_MIN_SECURITY_LEVEL,
 		   &sec, sizeof(sec));
 
···
      This sets the maximum lifespan on a call to hard_timeout (which is in
      jiffies).  In the event of the timeout occurring, the call will be
      aborted and -ETIME or -ETIMEDOUT will be returned.
+
+ (#) Apply the RXRPC_MIN_SECURITY_LEVEL sockopt to a socket from within in the
+     kernel::
+
+       int rxrpc_sock_set_min_security_level(struct sock *sk,
+					     unsigned int val);
+
+     This specifies the minimum security level required for calls on this
+     socket.
 
 
 Configurable Parameters

fs/afs/rxrpc.c

···
 {
 	struct sockaddr_rxrpc srx;
 	struct socket *socket;
-	unsigned int min_level;
 	int ret;
 
 	_enter("");
···
 	srx.transport.sin6.sin6_family	= AF_INET6;
 	srx.transport.sin6.sin6_port	= htons(AFS_CM_PORT);
 
-	min_level = RXRPC_SECURITY_ENCRYPT;
-	ret = kernel_setsockopt(socket, SOL_RXRPC, RXRPC_MIN_SECURITY_LEVEL,
-				(void *)&min_level, sizeof(min_level));
+	ret = rxrpc_sock_set_min_security_level(socket->sk,
+						RXRPC_SECURITY_ENCRYPT);
 	if (ret < 0)
 		goto error_2;
 

include/net/af_rxrpc.h

···
 void rxrpc_kernel_set_max_life(struct socket *, struct rxrpc_call *,
 			       unsigned long);
 
+int rxrpc_sock_set_min_security_level(struct sock *sk, unsigned int val);
+
 #endif /* _NET_RXRPC_H */

net/rxrpc/af_rxrpc.c

···
 	return ret;
 }
 
+int rxrpc_sock_set_min_security_level(struct sock *sk, unsigned int val)
+{
+	if (sk->sk_state != RXRPC_UNBOUND)
+		return -EISCONN;
+	if (val > RXRPC_SECURITY_MAX)
+		return -EINVAL;
+	lock_sock(sk);
+	rxrpc_sk(sk)->min_sec_level = val;
+	release_sock(sk);
+	return 0;
+}
+EXPORT_SYMBOL(rxrpc_sock_set_min_security_level);
+
 /*
  * set RxRPC socket options
  */