net: dns: Forward all DNS packets if callback is installed still not functional #107589

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1. Cristib05

   added

   bugThe issue is a bug, or the PR is fixing a bugThe issue is a bug, or the PR is fixing a bug

   on Apr 20, 2026
2. nordicjm

   added

   area: Networking

   on Apr 20, 2026
3. zephyrbot

   assigned

   rlubos

   and

   jukkar

   on Apr 20, 2026
4. rlubos commented on Apr 20, 2026

   

   rlubos

   on Apr 20, 2026

   Contributor

   More actions

   For sure additional check for query_idx is needed before passing the packet to pkt_fw_cb.

   Perhaps some reordering could be applied to dns_validate_msg() (like checking the record count after calculating the hash/query index) to mitigate the issue, however I don't think this can be fully avoided - the hash/index cannot be calculated for malformed packets.
5. Cristib05 commented on Apr 21, 2026

   

   Cristib05

   on Apr 21, 2026

   ContributorAuthor

   More actions

   I was thinking to do those operations if packet forwarding is enabled, a DNS packet is received (dns_id > 0), outside of dns_validate_msg() function.
6. Cristib05 commented on Apr 21, 2026

   

   Cristib05

   on Apr 21, 2026

   ContributorAuthor

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   something like this, in dns_read() function:

   	ret = dns_validate_msg(ctx, &dns_msg, dns_id, &query_idx,
   			       dns_cname, query_hash);
   
   #if defined(CONFIG_DNS_RESOLVER_PACKET_FORWARDING)
   	if (ctx->pkt_fw_cb != NULL) {
   		if (ret != 0) {
   			if (*dns_id > 0 && dns_unpack_response_query(&dns_msg) == 0 ) {
   				update_query_idx(ctx, &dns_msg, dns_id, &query_idx, query_hash);
   			}
   		}
   		if (query_idx != -1) {
   			ctx->pkt_fw_cb(dns_data, data_len, ctx->queries[query_idx].user_data);
   		}
   	}
   #endif /* CONFIG_DNS_RESOLVER_PACKET_FORWARDING */
   
7. rlubos commented on Apr 21, 2026

   

   rlubos

   on Apr 21, 2026

   Contributor

   More actions

   dns_unpack_response_query

   something like this, in dns_read() function:

   	ret = dns_validate_msg(ctx, &dns_msg, dns_id, &query_idx,
   			       dns_cname, query_hash);
   
   #if defined(CONFIG_DNS_RESOLVER_PACKET_FORWARDING)
   	if (ctx->pkt_fw_cb != NULL) {
   		if (ret != 0) {
   			if (*dns_id > 0 && dns_unpack_response_query(&dns_msg) == 0 ) {
   				update_query_idx(ctx, &dns_msg, dns_id, &query_idx, query_hash);
   			}
   		}
   		if (query_idx != -1) {
   			ctx->pkt_fw_cb(dns_data, data_len, ctx->queries[query_idx].user_data);
   		}
   	}
   #endif /* CONFIG_DNS_RESOLVER_PACKET_FORWARDING */
   

   It seems it could work that way, one caveat though. When dns_validate_msg() fails we don't know whether message size has been validated yet (happens in dns_unpack_response_header()), and dns_unpack_response_query() relies on that, so additional check for msg->msg_size > DNS_MSG_HEADER_SIZE before calling that would be needed I think.
8. henrikbrixandersen

   closed this as completedin #107749on Apr 24, 2026