net: dns: Fix DNS dispatcher for multiple network interfaces #79588
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When having multiple interfaces the dns dispatcher falsely flags interfaces with the same port and address_family as duplicates. This leads to problems when for example using MDNS. Signed-off-by: Carlo Kirchmeier <carlo.kirchmeier@zuehlke.com> Co-authored-by: Nils Ruf <nils.ruf@endress.com>
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| net_sin(&ctx->local_addr)->sin_port) { | ||
| dup = true; | ||
| continue; | ||
| if (ctx->sock == entry->sock) { |
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Doesn't explicit check for socket FD make other checks kind of pointless? It's not that you can have a socket that is bound to two different ports...
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We should probably check the addresses instead of socket descriptor values.
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Will this also be called for interfaces that are down or have no address assigned?
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we would compare
net_sin(&ctx->local_addr)->sin_addr.s_addr == net_sin(&entry->local_addr)->sin_addr.s_addras well as theportright? And since no two interfaces should have the same IP assigned this would also solve the issue.
It needs to be a bit more complicated as IPv6 needs to be checked too. Your example address check only validates IPv4 address.
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Will this also be called for interfaces that are
downor have no address assigned?
Please elaborate what you mean, I do not understand your question.
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Will this also be called for interfaces that are
downor have no address assigned?Please elaborate what you mean, I do not understand your question.
^ was a misconception of mine and can be ignored
But as far as i can see in the MDNS responder the function register_dispatcher and subsequently dns_dispatcher_register is called for each interface twice (once IPv4 and IPv6) and the local_addr is the same for both interfaces since it is the multicast 224.0.0.251 respectively ff02::fb. So both interfaces would have the same IP during the dispatch_register and the comparison would detect a false duplicate again right?
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Good point, the addresses would be the same in this case.
Hmm, I am trying to understand the actual issue. So you see the problem when having two network interfaces, what exactly is printed (if you enable debugging) error / warning etc. in this case?
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In short: The second interface was detected as a duplicate by the dispatcher since it had the same address family and port as the first interface (due to MDNS multicast).
@NilsRuf-EH as I will be absent the next few days could you have a look again at what the log output was in detail?
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If we have ports and family the same, then to separate them, the network interface is the only left thing that we can use.
When having multiple interfaces the dns dispatcher falsely flags interfaces with the same port and address_family as duplicates. This leads to problems when for example using MDNS.
@NilsRuf-EH thanks for pointing that out.