net: sunrpc: Fix off-by-one issues in 'rpc_ntop6'

Fix off-by-one issues in 'rpc_ntop6':
- 'snprintf' returns the number of characters which would have been
written if enough space had been available, excluding the terminating
null byte. Thus, a return value of 'sizeof(scopebuf)' means that the
last character was dropped.
- 'strcat' adds a terminating null byte to the string, thus if len ==
buflen, the null byte is written past the end of the buffer.

Signed-off-by: Fedor Tokarev <[e-mail]>
Signed-off-by: Anna Schumaker <[e-mail]>

net/sunrpc/addr.c

···
 
 	rc = snprintf(scopebuf, sizeof(scopebuf), "%c%u",
 			IPV6_SCOPE_DELIMITER, sin6->sin6_scope_id);
-	if (unlikely((size_t)rc > sizeof(scopebuf)))
+	if (unlikely((size_t)rc >= sizeof(scopebuf)))
 		return 0;
 
 	len += rc;
-	if (unlikely(len > buflen))
+	if (unlikely(len >= buflen))
 		return 0;
 
 	strcat(buf, scopebuf);