Revert "ping: fix ping6 name resolution for hostnames with link-local…

… addresses"

This reverts commit d217170.

This removes hints.ai_family = AF_UNSPEC and check for whether the
family matches (hopefully the check itself can be removed).

Reverting allows pinging IPv4-mapped IPv6 address because getaddrinfo()
implementation in glibc supports it already, only AF_UNSPEC enforcement
from d217170 disabled effect of -4 [1]:

$ ./builddir/ping/ping -4 -c1 ::ffff:127.0.0.1
PING ::ffff:127.0.0.1 (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.061 ms

--- ::ffff:127.0.0.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.061/0.061/0.061/0.000 ms

With this change the behavior matches ping from inetutils [2] and BusyBox.

Unfortunately this will not help on musl, which probably does not
support IPv4-mapped IPv6 address (although musl wiki does not mention
anything about IPv4-mapped IPv6 address support or about any related
difference from glibc [3], but libuv issue [4] mentions missing support
by default, glibc is mentioned to use ai_flags in AI_ADDRCONFIG |
AI_V4MAPPED, but even this does not help).

Original effort from issue iputils#252 [5] PR#253 [6] intended to fix pinging
IPv6 local scope address without scope ID on raw socket. Fix d217170
enabled it on raw socket, but surprisingly it works even without it:

$ ./builddir/ping/ping -v -c1 fe80::fc54:ff:fe29:5693
./builddir/ping/ping: sock4.fd: 3 (socktype: SOCK_RAW), sock6.fd: 4 (socktype: SOCK_RAW), hints.ai_family: AF_UNSPEC

ai->ai_family: AF_INET6, ai->ai_canonname: 'fe80::fc54:ff:fe29:5693'
PING fe80::fc54:ff:fe29:5693 (fe80::fc54:ff:fe29:5693) 56 data bytes
64 bytes from fe80::fc54:ff:fe29:5693%vnet0: icmp_seq=1 ident=53558 ttl=64 time=0.066 ms

--- fe80::fc54:ff:fe29:5693 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.066/0.066/0.066/0.000 ms

This issue was later considered less important (see c4b8b44),
because it does not work on ICMP datagram socket anyway.

[1] https://lists.busybox.net/pipermail/busybox/2024-October/090985.html
[2] https://lists.busybox.net/pipermail/busybox/2024-October/090985.html
[3] https://wiki.musl-libc.org/functional-differences-from-glibc.html#Name_Resolver/DNS
[4] libuv/libuv#2225
[5] iputils#252
[6] iputils#253

Suggested-by: Vo Ya <[email protected]>
Signed-off-by: Petr Vorel <[email protected]>

ping/ping.c

@@ -677,14 +677,6 @@ main(int argc, char **argv)
 	if (rts.tclass)
 		set_socket_option(&sock6, IPPROTO_IPV6, IPV6_TCLASS, &rts.tclass, sizeof(rts.tclass));
 
-	/* getaddrinfo fails to indicate a scopeid when not used in dual-stack mode.
-	 * Work around by always using dual-stack name resolution.
-	 *
-	 * https://github.com/iputils/iputils/issues/252
-	 */
-	int target_ai_family = hints.ai_family;
-	hints.ai_family = AF_UNSPEC;
-
 	if (!strchr(target, '%') && sock6.socktype == SOCK_DGRAM &&
 		inet_pton(AF_INET6, target, buf) > 0 &&
 		(IN6_IS_ADDR_LINKLOCAL(buf) || IN6_IS_ADDR_MC_LINKLOCAL(buf))) {
@@ -703,16 +695,6 @@ main(int argc, char **argv)
 				   str_family(ai->ai_family),
 				   ai->ai_canonname ? ai->ai_canonname : "");
 
-		if (target_ai_family != AF_UNSPEC &&
-			target_ai_family != ai->ai_family) {
-			if (!ai->ai_next) {
-				/* An address was found, but not of the family we really want.
-				 * Throw the appropriate gai error.
-				 */
-				error(2, 0, "%s: %s", target, gai_strerror(EAI_ADDRFAMILY));
-			}
-			continue;
-		}
 		switch (ai->ai_family) {
 		case AF_INET:
 			ret_val = ping4_run(&rts, argc, argv, ai, &sock4);