options to harden against very small EDNS bufsize or very large query packets.

git-svn-id: file:///svn/unbound/trunk@400 be551aaa-1e26-0410-a405-d3ace91eadb9

daemon/worker.c

@@ -63,6 +63,9 @@
 #include <netdb.h>
 #include <signal.h>
 
+/** Size of an UDP datagram */
+#define NORMAL_UDP_SIZE	512 /* bytes */
+
 void 
 worker_send_cmd(struct worker* worker, ldns_buffer* buffer,
 	enum worker_commands cmd)
@@ -394,14 +397,20 @@ worker_handle_service_reply(struct comm_point* c, void* arg, int error,
 
 /** check request sanity. Returns error code, 0 OK, or -1 discard. 
  * @param pkt: the wire packet to examine for sanity.
+ * @param worker: parameters for checking.
 */
 static int 
-worker_check_request(ldns_buffer* pkt)
+worker_check_request(ldns_buffer* pkt, struct worker* worker)
 {
 	if(ldns_buffer_limit(pkt) < LDNS_HEADER_SIZE) {
 		verbose(VERB_DETAIL, "request too short, discarded");
 		return -1;
 	}
+	if(ldns_buffer_limit(pkt) > NORMAL_UDP_SIZE && 
+		worker->daemon->cfg->harden_large_queries) {
+		verbose(VERB_DETAIL, "request too large, discarded");
+		return -1;
+	}
 	if(LDNS_QR_WIRE(ldns_buffer_begin(pkt))) {
 		verbose(VERB_DETAIL, "request has QR bit on, discarded");
 		return -1;
@@ -525,7 +534,7 @@ worker_handle_request(struct comm_point* c, void* arg, int error,
 		log_err("handle request called with err=%d", error);
 		return 0;
 	}
-	if((ret=worker_check_request(c->buffer)) != 0) {
+	if((ret=worker_check_request(c->buffer, worker)) != 0) {
 		verbose(VERB_ALGO, "worker check request: bad query.");
 		if(ret != -1) {
 			LDNS_QR_SET(ldns_buffer_begin(c->buffer));
@@ -571,6 +580,12 @@ worker_handle_request(struct comm_point* c, void* arg, int error,
 		attach_edns_record(c->buffer, &edns);
 		return 1;
 	}
+	if(edns.edns_present && edns.udp_size < NORMAL_UDP_SIZE &&
+		worker->daemon->cfg->harden_short_bufsize) {
+		verbose(VERB_DETAIL, "worker request: EDNS bufsize %d ignored",
+			(int)edns.udp_size);
+		edns.udp_size = NORMAL_UDP_SIZE;
+	}
 	if(edns.edns_present && edns.udp_size < LDNS_HEADER_SIZE) {
 		verbose(VERB_ALGO, "worker request: edns is too small.");
 		LDNS_QR_SET(ldns_buffer_begin(c->buffer));

doc/example.conf

@@ -128,6 +128,12 @@ server:
 	#	positive value: fetch that many targets opportunistically.
 	# Enclose the list of numbers between quotes ("").
 	# target-fetch-policy: "3 2 1 0 0"
+	
+	# Harden against very small EDNS buffer sizes. 
+	# harden_short_bufsize: no
+	
+	# Harden against unseemly large queries.
+	# harden_large_queries: no
 
 # Stub zones.
 # Create entries like below, to make all queries for 'example.com' and 

doc/unbound.conf.5

@@ -134,6 +134,14 @@ that many targets opportunistically. Enclose the list between quotes ("").
 The default is "3 2 1 0 0". Setting all zeroes, "0 0 0 0 0" gives behaviour
 closer to that of BIND 9, while setting "-1 -1 -1 -1 -1" gives behaviour 
 rumoured to be closer to that of BIND 8.
+.It \fBharden-short-bufsize:\fR <yes or no>
+Very small EDNS buffer sizes from queries are ignored. Default is off, since
+it is legal protocol wise to send these, and unbound tries to give very 
+small answers to these queries, where possible.
+.It \fBharden-large-queries:\fR <yes or no>
+Very large queries are ignored. Default is off, since it is legal protocol
+wise to send these, and could be necessary for operation if TSIG or EDNS
+payload is very large.
 .El
 
 .Ss Stub Zone Options

util/config_file.c

@@ -100,6 +100,8 @@ config_create()
 	cfg->num_ifs = 0;
 	cfg->ifs = NULL;
 	cfg->stubs = NULL;
+	cfg->harden_short_bufsize = 0;
+	cfg->harden_large_queries = 0;
 	return cfg;
 error_exit:
 	config_delete(cfg); 

util/config_file.h

@@ -110,6 +110,11 @@ struct config_file {
 	/** the stub definitions, linked list */
 	struct config_stub* stubs;
 
+	/** harden against very small edns buffer sizes */
+	int harden_short_bufsize;
+	/** harden against very large query sizes */
+	int harden_large_queries;
+
 	/** chrootdir, if not "" or chroot will be done */
 	char* chrootdir;
 	/** username to change to, if not "". */

util/configlexer.lex

@@ -128,6 +128,8 @@ infra-cache-numhosts{COLON}	{ YDOUT; return VAR_INFRA_CACHE_NUMHOSTS;}
 infra-cache-numlame{COLON}	{ YDOUT; return VAR_INFRA_CACHE_NUMLAME;}
 num-queries-per-thread{COLON}	{ YDOUT; return VAR_NUM_QUERIES_PER_THREAD;}
 target-fetch-policy{COLON}	{ YDOUT; return VAR_TARGET_FETCH_POLICY;}
+harden-short-bufsize{COLON}	{ YDOUT; return VAR_HARDEN_SHORT_BUFSIZE;}
+harden-large-queries{COLON}	{ YDOUT; return VAR_HARDEN_LARGE_QUERIES;}
 stub-zone{COLON}	{ YDOUT; return VAR_STUB_ZONE;}
 name{COLON}		{ YDOUT; return VAR_NAME;}
 stub-addr{COLON}	{ YDOUT; return VAR_STUB_ADDR;}

util/configparser.y

@@ -77,6 +77,7 @@ extern struct config_parser_state* cfg_parser;
 %token VAR_INFRA_HOST_TTL VAR_INFRA_LAME_TTL VAR_INFRA_CACHE_SLABS
 %token VAR_INFRA_CACHE_NUMHOSTS VAR_INFRA_CACHE_NUMLAME VAR_NAME
 %token VAR_STUB_ZONE VAR_STUB_HOST VAR_STUB_ADDR VAR_TARGET_FETCH_POLICY
+%token VAR_HARDEN_SHORT_BUFSIZE VAR_HARDEN_LARGE_QUERIES
 
 %%
 toplevelvars: /* empty */ | toplevelvars toplevelvar ;
@@ -104,7 +105,8 @@ content_server: server_num_threads | server_verbosity | server_port |
 	server_infra_host_ttl | server_infra_lame_ttl | 
 	server_infra_cache_slabs | server_infra_cache_numhosts |
 	server_infra_cache_numlame | stubstart contents_stub | 
-	server_target_fetch_policy
+	server_target_fetch_policy | server_harden_short_bufsize |
+	server_harden_large_queries
 	;
 stubstart: VAR_STUB_ZONE
 	{
@@ -385,6 +387,26 @@ server_target_fetch_policy: VAR_TARGET_FETCH_POLICY STRING
 		cfg_parser->cfg->target_fetch_policy = $2;
 	}
 	;
+server_harden_short_bufsize: VAR_HARDEN_SHORT_BUFSIZE STRING
+	{
+		OUTYY(("P(server_harden_short_bufsize:%s)\n", $2));
+		if(strcmp($2, "yes") != 0 && strcmp($2, "no") != 0)
+			yyerror("expected yes or no.");
+		else cfg_parser->cfg->harden_short_bufsize = 
+			(strcmp($2, "yes")==0);
+		free($2);
+	}
+	;
+server_harden_large_queries: VAR_HARDEN_LARGE_QUERIES STRING
+	{
+		OUTYY(("P(server_harden_large_queries:%s)\n", $2));
+		if(strcmp($2, "yes") != 0 && strcmp($2, "no") != 0)
+			yyerror("expected yes or no.");
+		else cfg_parser->cfg->harden_large_queries = 
+			(strcmp($2, "yes")==0);
+		free($2);
+	}
+	;
 stub_name: VAR_NAME STRING
 	{
 		OUTYY(("P(name:%s)\n", $2));