libbb:/send_to_from: do not require that "to" should have the same AF. Closes 9146

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/libbb/udp_io.c b/libbb/udp_io.c
index a32af9bd2..6e3ef484e 100644
--- a/libbb/udp_io.c
+++ b/libbb/udp_io.c
@@ -70,7 +70,13 @@ send_to_from(int fd, void *buf, size_t len, int flags,
         msg.msg_flags = flags;
 
         cmsgptr = CMSG_FIRSTHDR(&msg);
-        if (to->sa_family == AF_INET && from->sa_family == AF_INET) {
+        /*
+         * Users report that to->sa_family can be AF_INET6 too,
+         * if "to" was acquired by recv_from_to(). IOW: recv_from_to()
+         * was seen showing IPv6 "from" even when the destination
+         * of received packet (our local address) was IPv4.
+         */
+        if (/* to->sa_family == AF_INET && */ from->sa_family == AF_INET) {
                 struct in_pktinfo *pktptr;
                 cmsgptr->cmsg_level = IPPROTO_IP;
                 cmsgptr->cmsg_type = IP_PKTINFO;
@@ -86,7 +92,7 @@ send_to_from(int fd, void *buf, size_t len, int flags,
                 pktptr->ipi_spec_dst = ((struct sockaddr_in*)from)->sin_addr;
         }
 # if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
-        else if (to->sa_family == AF_INET6 && from->sa_family == AF_INET6) {
+        else if (/* to->sa_family == AF_INET6 && */ from->sa_family == AF_INET6) {
                 struct in6_pktinfo *pktptr;
                 cmsgptr->cmsg_level = IPPROTO_IPV6;
                 cmsgptr->cmsg_type = IPV6_PKTINFO;