rds: fix an integer overflow test in rds_info_getsockopt()

"len" is a signed integer. We check that len is not negative, so it goes from zero to INT_MAX. PAGE_SIZE is unsigned long so the comparison is type promoted to unsigned long. ULONG_MAX - 4095 is a higher than INT_MAX so the condition can never be true.

I don't know if this is harmful but it seems safe to limit "len" to INT_MAX - 4095.

index 9a6b4f6..140a44a 100644
@@ -176,7 +176,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
 
 	/* check for all kinds of wrapping and the like */
 	start = (unsigned long)optval;
-	if (len < 0 || len + PAGE_SIZE - 1 < len || start + len < start) {
+	if (len < 0 || len > INT_MAX - PAGE_SIZE + 1 || start + len < start) {
 		ret = -EINVAL;
 		goto out;
 	}

From: Dan Carpenter <[email protected]>
Date: Sat, 1 Aug 2015 15:33:26 +0300

Applied, thanks Dan.