[Bug libc/13651] New: resolver fails if result to first query fails but second succeeds

["aurelien at aurel32 dot net" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=13651

             Bug #: 13651
           Summary: resolver fails if result to first query fails but
                    second succeeds
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: aurelien@aurel32.net
    Classification: Unclassified


Created attachment 6187
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6187
Patch to fix the issue

When using a nameserver which doesn't support IPv6, it might returns FORMERR or
NOTIMP, though it's not supposed to be the case according to the RFC. When this
corresponds to the first answer (which is usually the case as it's faster to
just return an error than doing a recursive query), resplen (that is the
returned value) ends up being 0 and resplen2 > 0. The tests in
__libc_res_nsearch() only look at resplen and totally ignore resplen2.

The attached patch fixes that by testing if resplen > 0 or resplen == 0 (that
is empty result, but no error) and resplen2 > 0.

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