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dns: fail if ipv6 is disabled and resolv.conf has only v6 nameserves

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if resolv.conf lists no nameservers at all, the default of 127.0.0.1
is used. however, another "no nameservers" case arises where the
system has ipv6 support disabled/configured-out and resolv.conf only
contains v6 nameservers. this caused the resolver to repeat socket
operations that will necessarily fail (sending to one or more
wrong-family addresses) while waiting for a timeout.

it would be contrary to configured intent to query 127.0.0.1 in this
case, but the current behavior is not conducive to diagnosing the
configuration problem. instead, fail immediately with EAI_SYSTEM and
errno==EAFNOSUPPORT so that the configuration error is reportable.
This commit is contained in:
Rich Felker 2022-08-26 14:57:52 -04:00
parent 996b6154b2
commit a636fd630f
1 changed files with 5 additions and 0 deletions
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5
src/network/res_msend.c
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@ -72,6 +72,11 @@ int __res_msend_rc(int nqueries, const unsigned char *const *queries,
/* Handle case where system lacks IPv6 support */
if (fd < 0 && family == AF_INET6 && errno == EAFNOSUPPORT) {
for (i=0; i<nns && conf->ns[nns].family == AF_INET6; i++);
if (i==nns) {
pthread_setcancelstate(cs, 0);
return -1;
}
fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
family = AF_INET;
sl = sizeof sa.sin;