net: dns: Convert the query and answer to small case letters

Because we might get answers in capital letters, convert the answer
to small case letters and also make sure we send query in small case
latters. This makes sure that our query_hash is properly calculated
regardless of how the resolver gets the data.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

subsys/net/lib/dns/resolve.c

@@ -19,6 +19,7 @@ LOG_MODULE_REGISTER(net_dns_resolve, CONFIG_DNS_RESOLVER_LOG_LEVEL);
 #include <string.h>
 #include <errno.h>
 #include <stdlib.h>
+#include <ctype.h>
 
 #include <zephyr/sys/crc.h>
 #include <zephyr/net/net_ip.h>
@@ -653,7 +654,7 @@ int dns_validate_msg(struct dns_resolve_context *ctx,
 	struct dns_addrinfo info = { 0 };
 	uint32_t ttl; /* RR ttl, so far it is not passed to caller */
 	uint8_t *src, *addr;
-	const char *query_name;
+	char *query_name;
 	int address_size;
 	/* index that points to the current answer being analyzed */
 	int answer_ptr;
@@ -743,6 +744,13 @@ int dns_validate_msg(struct dns_resolve_context *ctx,
 
 			query_name = dns_msg->msg + dns_msg->query_offset;
 
+			/* Convert the query name to small case so that our
+			 * hash checker can find it.
+			 */
+			for (size_t i = 0, n = strlen(query_name); i < n; i++) {
+				query_name[i] = tolower(query_name[i]);
+			}
+
 			/* Add \0 and query type (A or AAAA) to the hash */
 			*query_hash = crc16_ansi(query_name,
 						 strlen(query_name) + 1 + 2);
@@ -955,6 +963,7 @@ static int dns_write(struct dns_resolve_context *ctx,
 	int server_addr_len;
 	uint16_t dns_id, len;
 	int ret, sock, family;
+	char *query_name;
 
 	sock = ctx->servers[server_idx].sock;
 	family = ctx->servers[server_idx].dns_server.sa_family;
@@ -971,11 +980,20 @@ static int dns_write(struct dns_resolve_context *ctx,
 		return -EINVAL;
 	}
 
+	query_name = buf + DNS_MSG_HEADER_SIZE;
+
+	/* Convert the query name to small case so that our
+	 * hash checker can find it later when we get the answer.
+	 */
+	for (int i = 0; i < dns_qname->len; i++) {
+		query_name[i] = tolower(query_name[i]);
+	}
+
 	/* Add \0 and query type (A or AAAA) to the hash. Note that
 	 * the dns_qname->len contains the length of \0
 	 */
 	ctx->queries[query_idx].query_hash =
-		crc16_ansi(buf + DNS_MSG_HEADER_SIZE, dns_qname->len + 2);
+		crc16_ansi(query_name, dns_qname->len + 2);
 
 	if (hop_limit > 0) {
 		if (IS_ENABLED(CONFIG_NET_IPV6) && family == AF_INET6) {