rxrpc: Fix checker warning

Fix the following checker warning:

../net/rxrpc/key.c:692:9: error: subtraction of different types can't work (different address spaces)

Checker is wrong in this case, but cast the pointers to unsigned long to
avoid the warning.

Whilst we're at it, reduce the assertions to WARN_ON() and return an error.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org

net/rxrpc/key.c

@@ -602,7 +602,8 @@ static long rxrpc_read(const struct key *key,
 		}
 
 		_debug("token[%u]: toksize=%u", ntoks, toksize);
-		ASSERTCMP(toksize, <=, AFSTOKEN_LENGTH_MAX);
+		if (WARN_ON(toksize > AFSTOKEN_LENGTH_MAX))
+			return -EIO;
 
 		toksizes[ntoks++] = toksize;
 		size += toksize + 4; /* each token has a length word */
@@ -679,8 +680,9 @@ static long rxrpc_read(const struct key *key,
 			return -ENOPKG;
 		}
 
-		ASSERTCMP((unsigned long)xdr - (unsigned long)oldxdr, ==,
-			  toksize);
+		if (WARN_ON((unsigned long)xdr - (unsigned long)oldxdr ==
+			    toksize))
+			return -EIO;
 	}
 
 #undef ENCODE_STR
@@ -688,8 +690,10 @@ static long rxrpc_read(const struct key *key,
 #undef ENCODE64
 #undef ENCODE
 
-	ASSERTCMP(tok, ==, ntoks);
-	ASSERTCMP((char __user *) xdr - buffer, ==, size);
+	if (WARN_ON(tok != ntoks))
+		return -EIO;
+	if (WARN_ON((unsigned long)xdr - (unsigned long)buffer != size))
+		return -EIO;
 	_leave(" = %zu", size);
 	return size;
 }