daemon: fix IPv6 address corruption in lookup_hostname()

getaddrinfo() is called with AF_UNSPEC hints, so it may return IPv6
results. However, the code unconditionally casts ai_addr to
sockaddr_in and passes AF_INET to inet_ntop(). On IPv6-only hosts,
this reads from the wrong struct offset, producing garbage IP
addresses.

Fix this by checking ai_family and extracting the address pointer
into a local variable before calling inet_ntop() once with the
correct family. Die on unexpected address families.

Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/daemon.c b/daemon.c
index 0a7b1aae44..80fa0226d8 100644
--- a/daemon.c
+++ b/daemon.c
@@ -674,9 +674,20 @@ static void lookup_hostname(struct hostinfo *hi)
 
 		gai = getaddrinfo(hi->hostname.buf, NULL, &hints, &ai);
 		if (!gai) {
-			struct sockaddr_in *sin_addr = (void *)ai->ai_addr;
+			void *addr;
 
-			inet_ntop(AF_INET, &sin_addr->sin_addr,
+			if (ai->ai_family == AF_INET) {
+				struct sockaddr_in *sa = (void *)ai->ai_addr;
+				addr = &sa->sin_addr;
+			} else if (ai->ai_family == AF_INET6) {
+				struct sockaddr_in6 *sa6 = (void *)ai->ai_addr;
+				addr = &sa6->sin6_addr;
+			} else {
+				die("unexpected address family: %d",
+				    ai->ai_family);
+			}
+
+			inet_ntop(ai->ai_family, addr,
 				  addrbuf, sizeof(addrbuf));
 			strbuf_addstr(&hi->ip_address, addrbuf);