reject message with different values in multiple Content-Length header field

If multiple headers occur, usually the last header would have authority;
however the section 3.3.3 of RFC 7230 states that:

If a message is received without Transfer-Encoding and with
either multiple Content-Length header fields having differing
field-values or ..., then the message framing is invalid and the
recipient MUST treat it as an unrecoverable error.

For example:
If there are 2 headers, for example, "Content-Length: 42" and "Content-Length: 52",
then current shim httpboot.c will accept the last one which is "Content-Length": 52".
This is not correct.

This patch allows multiple values if they are the same, but rejects message
if any different value is found. In function receive_http_response() of httpboot.c,
each received duplicate Content-Length field must be checked whether its value is
different. If it is, then this message is invalid.

Signed-off-by: Dennis Tseng <dennis.tseng@suse.com>

Author: dennis-tseng99

httpboot.c

@@ -562,7 +562,7 @@ receive_http_response(EFI_HTTP_PROTOCOL *http, VOID **buffer, UINT64 *buf_size)
 	EFI_HTTP_RESPONSE_DATA response;
 	EFI_HTTP_STATUS_CODE http_status;
 	BOOLEAN response_done;
-	UINTN i, downloaded;
+	UINTN i, j, downloaded;
 	CHAR8 rx_buffer[9216];
 	EFI_STATUS efi_status;
 	EFI_STATUS event_status;
@@ -619,6 +619,15 @@ receive_http_response(EFI_HTTP_PROTOCOL *http, VOID **buffer, UINT64 *buf_size)
 		if (!strcasecmp(rx_message.Headers[i].FieldName,
 				(CHAR8 *)"Content-Length")) {
 			*buf_size = ascii_to_int(rx_message.Headers[i].FieldValue);
+			for(j = 0; j < i; j++) {
+				if (!strcasecmp(rx_message.Headers[i].FieldName,
+						(CHAR8 *)"Content-Length")) {
+					if (*buf_size != ascii_to_int(rx_message.Headers[j].FieldValue)) {
+						perror(L"Content-Length is invalid\n");
+						goto error;
+					}
+				}
+			}
 		}
 	}