Last bad IPv6 query response can make c-ares to report resolution failure even if there is previously successful IPv4 response

[Brad House]

Appears to be a duplicate, a reply was sent out to the original:
https://lists.haxx.se/pipermail/c-ares/2022-April/000035.html

On 5/2/22 8:08 PM, Dmitry Karpov via c-ares wrote:
>
> Hi,
>
>
> I recently stepped on an issue with curl using c-ares 
> ares_getaddrinfo() with PF_UNSPEC family, when AAAA response from DNS 
> server contained some bad data resulting into ARES_EBADRESP status 
> code whereas A response was good.
>
> The problem was that when AAAA response was the last received, it made 
> c-ares to ignore previously received good A response and fail the host 
> resolution with ARES_EBADRESP status code.
> But if A response was the last received, then c-ares ignored the bad 
> AAAA response and the host resolution was successful.
>
> I looked at the c-ares code, and found the problem in the 
> host_callback() function (src\lib\ares_getaddrinfo.c: 528)
>
> static void host_callback(void *arg, int status, int timeouts,
>
>                           unsigned char *abuf, int alen)
>
> {
>
>   struct host_query *hquery = (struct host_query*)arg;
>
>   int addinfostatus = ARES_SUCCESS;
>
>   hquery->timeouts += timeouts;
>
>   hquery->remaining--;
>
>   if (status == ARES_SUCCESS)
>
>     {
>
>       addinfostatus = ares__parse_into_addrinfo(abuf, alen, 1, 
> hquery->port, hquery->ai);
>
>     }
>
>   if (!hquery->remaining)
>
>     {
>
>       if (addinfostatus != ARES_SUCCESS && addinfostatus != ARES_ENODATA)
>
>         {
>
>           /* error in parsing result e.g. no memory */
>
>           end_hquery(hquery, addinfostatus);
>
>         }
>
>       else if (hquery->ai->nodes)
>
>      …
>
> When there are no remaining queries, the ARES_EBADRESP parsing error 
> is reported immediately, even though the previous query might be 
> successful.
>
> I suggest the following fix for this problem:
>
> if (!hquery->remaining)
>
>     {
>
>       if (addinfostatus != ARES_SUCCESS && addinfostatus != ARES_ENODATA)
>
>         {
>
>           /* error in parsing result e.g. no memory */
>
>          if (addinfostatus == ARES_EBADRESP && hquery->ai->nodes)
>
>             {
>
>               /* We got a bad response from the server, but at least 
> one query
>
>                * ended with ARES_SUCCESS */
>
>               end_hquery(hquery, ARES_SUCCESS);
>
>             }
>
>           else
>
>             {
>
>               end_hquery(hquery, addinfostatus);
>
>             }
>
>         }
>
> I am also attaching a patch file with the potential fix.
>
> Thanks,
> Dmitry Karpov
>
>
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