net: dns: Check that dispatcher table is not overflowing

Add CHECKIF() checks that verify that dispatcher table is
not overflowing.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>

subsys/net/lib/dns/dispatcher.c

@@ -255,6 +255,11 @@ int dns_dispatcher_register(struct dns_socket_dispatcher *ctx)
  entry->pair = ctx;
 
  for (int i = 0; i < ctx->fds_len; i++) {
+ CHECKIF(ctx->fds[i].fd >= ARRAY_SIZE(dispatch_table)) {
+ ret = -ERANGE;
+ goto out;
+ }
+
  if (dispatch_table[ctx->fds[i].fd].ctx == NULL) {
  dispatch_table[ctx->fds[i].fd].ctx = ctx;
  }
@@ -287,6 +292,11 @@ int dns_dispatcher_register(struct dns_socket_dispatcher *ctx)
  ctx->pair = NULL;
 
  for (int i = 0; i < ctx->fds_len; i++) {
+ CHECKIF(ctx->fds[i].fd >= ARRAY_SIZE(dispatch_table)) {
+ ret = -ERANGE;
+ goto out;
+ }
+
  if (dispatch_table[ctx->fds[i].fd].ctx == NULL) {
  dispatch_table[ctx->fds[i].fd].ctx = ctx;
  }
@@ -308,17 +318,25 @@ int dns_dispatcher_register(struct dns_socket_dispatcher *ctx)
 
 int dns_dispatcher_unregister(struct dns_socket_dispatcher *ctx)
 {
+ int ret = 0;
+
  k_mutex_lock(&lock, K_FOREVER);
 
  (void)sys_slist_find_and_remove(&sockets, &ctx->node);
 
  for (int i = 0; i < ctx->fds_len; i++) {
+ CHECKIF(ctx->fds[i].fd >= ARRAY_SIZE(dispatch_table)) {
+ ret = -ERANGE;
+ goto out;
+ }
+
  dispatch_table[ctx->fds[i].fd].ctx = NULL;
  }
 
+out:
  k_mutex_unlock(&lock);
 
- return 0;
+ return ret;
 }
 
 void dns_dispatcher_init(void)