dhcp: get_option_uint32/16 only accept options with correct len

RFC8925 mentions "The client MUST ignore the IPv6-Only Preferred option
if the length field value is not 4."

Author: taoyl-g

src/dhcp.c

@@ -304,7 +304,7 @@ get_option_uint32(struct dhcpcd_ctx *ctx,
 	uint32_t d;
 
 	p = get_option(ctx, bootp, bootp_len, option, &len);
-	if (!p || len < (ssize_t)sizeof(d))
+	if (!p || len != (ssize_t)sizeof(d))
 		return -1;
 	memcpy(&d, p, sizeof(d));
 	if (i)
@@ -321,7 +321,7 @@ get_option_uint16(struct dhcpcd_ctx *ctx,
 	uint16_t d;
 
 	p = get_option(ctx, bootp, bootp_len, option, &len);
-	if (!p || len < (ssize_t)sizeof(d))
+	if (!p || len != (ssize_t)sizeof(d))
 		return -1;
 	memcpy(&d, p, sizeof(d));
 	if (i)