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dns: fix workaround for systems defaulting to ipv6-only sockets

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When IPv6 nameservers are present, __res_msend_rc attempts to disable
IPV6_V6ONLY socket option to ensure that it can communicate with IPv4
nameservers (if they are present too) via IPv4-mapped IPv6 addresses.
However, this option can't be disabled on bound sockets, so setsockopt
always fails.
This commit is contained in:
Alexey Izbyshev 2023-02-25 01:07:33 +03:00 • committed by Rich Felker
parent bec42ef393
commit d0b7f9768d
1 changed files with 16 additions and 15 deletions
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31
src/network/res_msend.c
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@ -133,6 +133,22 @@ int __res_msend_rc(int nqueries, const unsigned char *const *queries,
family = AF_INET;
sl = sizeof sa.sin;
}
/* Convert any IPv4 addresses in a mixed environment to v4-mapped */
if (fd >= 0 && family == AF_INET6) {
setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
for (i=0; i<nns; i++) {
if (ns[i].sin.sin_family != AF_INET) continue;
memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
&ns[i].sin.sin_addr, 4);
memcpy(ns[i].sin6.sin6_addr.s6_addr,
"\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
ns[i].sin6.sin6_family = AF_INET6;
ns[i].sin6.sin6_flowinfo = 0;
ns[i].sin6.sin6_scope_id = 0;
}
}
sa.sin.sin_family = family;
if (fd < 0 || bind(fd, (void *)&sa, sl) < 0) {
if (fd >= 0) close(fd);
@ -152,21 +168,6 @@ int __res_msend_rc(int nqueries, const unsigned char *const *queries,
pthread_cleanup_push(cleanup, pfd);
pthread_setcancelstate(cs, 0);
/* Convert any IPv4 addresses in a mixed environment to v4-mapped */
if (family == AF_INET6) {
setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
for (i=0; i<nns; i++) {
if (ns[i].sin.sin_family != AF_INET) continue;
memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
&ns[i].sin.sin_addr, 4);
memcpy(ns[i].sin6.sin6_addr.s6_addr,
"\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
ns[i].sin6.sin6_family = AF_INET6;
ns[i].sin6.sin6_flowinfo = 0;
ns[i].sin6.sin6_scope_id = 0;
}
}
memset(alens, 0, sizeof *alens * nqueries);
retry_interval = timeout / attempts;