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
c-ares-1.18.1-last-bad-server-response-fix.patch
Description: c-ares-1.18.1-last-bad-server-response-fix.patch
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