r11495@Kushana: nickm | 2006-12-11 19:11:14 -0500

More evdns: tab fixes.  Dont make users worry about flags.  Set truncated flag correctly when generating responses, rather than just bailing out.


svn:r9084

doc/TODO

@@ -92,6 +92,7 @@ N - DNS improvements
     . Asynchronous DNS
       o Document and rename SearchDomains, ResolvConf options
       D Make API closer to getaddrinfo()
+      - Teach evdns about ipv6.
       - Teach evdns to be able to listen for requests to be processed.
         . Design interface.
           - Rename stuff; current names suck.
@@ -105,6 +106,8 @@ N - DNS improvements
           o Queue responses when we see EAGAIN
           o Retry responses after a while
           o Be efficient about labels.
+          o Fix the interface for flags and flag handling.
+          o Generate truncated responses correctly.
           - Comment everything.
           - Clean up XXXX items
           - Test

src/or/eventdns.c

@@ -1064,6 +1064,8 @@ request_parse(u8 *packet, int length, struct evdns_server_port *port, struct soc
 	GET16(additional);
 
 	if (flags & 0x8000) return -1; // Must not be an answer.
+	if (flags & 0x7800) return -1; // only standard queries are supported
+	flags &= 0x0300; // Only TC and RD get preserved.
 
 	server_req = malloc(sizeof(struct server_request));
 	if (server_req == NULL) return -1;
@@ -1384,7 +1386,7 @@ dnsname_to_labels(u8 *const buf, size_t buf_len, off_t j,
 
 #define APPEND16(x) do {                           \
         if (j + 2 > (off_t)buf_len)				   \
-            return (-2);                           \
+            goto overflow;                         \
         _t = htons(x);                             \
         memcpy(buf + j, &_t, 2);                   \
         j += 2;                                    \
@@ -1429,6 +1431,8 @@ dnsname_to_labels(u8 *const buf, size_t buf_len, off_t j,
 	// in which case the zero is already there
 	if (!j || buf[j-1]) buf[j++] = 0;
 	return j;
+ overflow:
+	return (-2);
 }
 
 // Finds the length of a dns request for a DNS name of the given
@@ -1454,13 +1458,12 @@ evdns_request_data_build(const char *const name, const int name_len, const u16 t
 
 #define APPEND32(x) do {                           \
         if (j + 4 > (off_t)buf_len)                \
-            return (-1);                           \
+            goto overflow;                         \
         _t32 = htonl(x);                           \
         memcpy(buf + j, &_t32, 4);                 \
         j += 4;                                    \
     } while (0)
 
-
 	APPEND16(trans_id);
 	APPEND16(0x0100);  // standard query, recusion needed
 	APPEND16(1);  // one question
@@ -1477,6 +1480,8 @@ evdns_request_data_build(const char *const name, const int name_len, const u16 t
 	APPEND16(class);
 
 	return (int)j;
+ overflow:
+	return (-1);
 }
 
 // exported function
@@ -1615,16 +1620,24 @@ evdns_request_add_cname_reply(struct evdns_server_request *req, const char *name
 }
 
 static int
-evdns_request_response_format(struct server_request *req, int flags)
+evdns_request_response_format(struct server_request *req, int err)
 {
 	unsigned char buf[1500];
 	size_t buf_len = sizeof(buf);
-	off_t j = 0;
+	off_t j = 0, r;
 	u16 _t;
 	u32 _t32;
 	int i;
+	u16 flags;
 	struct dnslabel_table table;
 
+    if (err < 0 || err > 15) return -1;
+
+	/* Set response bit and error code; copy OPCODE and RD fields from
+	 * question; copy RA and AA if set by caller. */
+	flags = req->base.flags;
+	flags |= (0x8000 | err);
+
 	dnslabel_table_init(&table); // XXXX need to call dnslable_table_clear.
 	APPEND16(req->trans_id);
 	APPEND16(flags);
@@ -1643,7 +1656,7 @@ evdns_request_response_format(struct server_request *req, int flags)
 		APPEND16(req->base.questions[i]->class);
 	}
 
-	/* Add answer-like sections. */
+	/* Add answer, authority, and additional sections. */
 	for (i=0; i<3; ++i) {
 		struct server_request_item *item;
 		if (i==0)
@@ -1653,9 +1666,10 @@ evdns_request_response_format(struct server_request *req, int flags)
 		else
 			item = req->additional;
 		while (item) {
-			j = dnsname_to_labels(buf, buf_len, j, item->name, strlen(item->name), &table);
-			if (j < 0)
-				return (int) j;
+			r = dnsname_to_labels(buf, buf_len, j, item->name, strlen(item->name), &table);
+			if (r < 0)
+				goto overflow;
+			j = r;
 
 			APPEND16(item->type);
 			APPEND16(item->class);
@@ -1664,15 +1678,16 @@ evdns_request_response_format(struct server_request *req, int flags)
 				off_t len_idx = j, name_start;
 				j += 2;
 				name_start = j;
-				j = dnsname_to_labels(buf, buf_len, j, item->data, strlen(item->data), &table);
-				if (j < 0)
-					return (int) j;
+				r = dnsname_to_labels(buf, buf_len, j, item->data, strlen(item->data), &table);
+				if (r < 0)
+					goto overflow;
+				j = r;
 				_t = htons( (j-name_start) );
 				memcpy(buf+len_idx, &_t, 2);
 			} else {
 				APPEND16(item->datalen);
 				if (j+item->datalen > (off_t)buf_len)
-					return -1;
+					goto overflow;
 				memcpy(buf+j, item->data, item->datalen);
 				j += item->datalen;
 			}
@@ -1680,11 +1695,20 @@ evdns_request_response_format(struct server_request *req, int flags)
 		}
 	}
 
-	req->response_len = j;
-	if (!(req->response = malloc(req->response_len)))
-		return -1;
-	memcpy(req->response, buf, req->response_len);
+	if (j > 512) {
+overflow:
+		j = 512;
+		buf[3] |= 0x02; /* set the truncated bit. */
+	}
 
+	req->response_len = j;
+
+	if (!(req->response = malloc(req->response_len))) {
+		evdns_server_request_free_answers(req);
+		dnslabel_clear(&table);
+		return -1;
+	}
+	memcpy(req->response, buf, req->response_len);
 	evdns_server_request_free_answers(req);
 	dnslabel_clear(&table);
 	return 0;
@@ -1692,13 +1716,13 @@ evdns_request_response_format(struct server_request *req, int flags)
 
 // exported function
 int
-evdns_request_respond(struct evdns_server_request *_req, int flags)
+evdns_request_respond(struct evdns_server_request *_req, int err)
 {
 	struct server_request *req = TO_SERVER_REQUEST(_req);
 	struct evdns_server_port *port = req->port;
 	int r;
 	if (!req->response) {
-		if ((r = evdns_request_response_format(req, flags))<0)
+		if ((r = evdns_request_response_format(req, err))<0)
 			return r;
 	}
 
@@ -2933,7 +2957,7 @@ evdns_server_callback(struct evdns_server_request *req, void *data)
 		}
 	}
 
-	r = evdns_request_respond(req, 0x8000);
+	r = evdns_request_respond(req, 0);
 	if (r<0)
 		printf("eeek, couldn't send reply.\n");
 }

src/or/eventdns.h

@@ -113,7 +113,7 @@ int evdns_request_add_aaaa_reply(struct evdns_server_request *req, const char *n
 int evdns_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl);
 int evdns_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl);
 
-int evdns_request_respond(struct evdns_server_request *req, int flags);
+int evdns_request_respond(struct evdns_server_request *req, int err);
 int evdns_request_drop(struct evdns_server_request *req);
 
 #endif  // !EVENTDNS_H