1 files changed, 11 insertions, 6 deletions

diff --git a/libbb/udp_io.c b/libbb/udp_io.c
index e968ecb66..bde4d779f 100644
--- a/libbb/udp_io.c
+++ b/libbb/udp_io.c
@@ -36,11 +36,12 @@ send_to_from(int fd, void *buf, size_t len, int flags,
 #else
         struct iovec iov[1];
         struct msghdr msg;
-        char cbuf[sizeof(struct in_pktinfo)
+        union {
+                char cmsg[CMSG_SPACE(sizeof(struct in_pktinfo))];
 #if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
-                | sizeof(struct in6_pktinfo) /* (a|b) is poor man's max(a,b) */
+                char cmsg6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
 #endif
-        ];
+        } u;
         struct cmsghdr* cmsgptr;
 
         if (from->sa_family != AF_INET
@@ -57,15 +58,15 @@ send_to_from(int fd, void *buf, size_t len, int flags,
         iov[0].iov_base = buf;
         iov[0].iov_len = len;
 
-        memset(cbuf, 0, sizeof(cbuf));
+        memset(&u, 0, sizeof(u));
 
         memset(&msg, 0, sizeof(msg));
         msg.msg_name = (void *)(struct sockaddr *)to; /* or compiler will annoy us */
         msg.msg_namelen = tolen;
         msg.msg_iov = iov;
         msg.msg_iovlen = 1;
-        msg.msg_control = cbuf;
-        msg.msg_controllen = sizeof(cbuf);
+        msg.msg_control = &u;
+        msg.msg_controllen = sizeof(u);
         msg.msg_flags = flags;
 
         cmsgptr = CMSG_FIRSTHDR(&msg);
@@ -89,6 +90,8 @@ send_to_from(int fd, void *buf, size_t len, int flags,
                 pktptr->ipi6_addr = ((struct sockaddr_in6*)from)->sin6_addr;
         }
 #endif
+        msg.msg_controllen = cmsgptr->cmsg_len;
+
         return sendmsg(fd, &msg, flags);
 #endif
 }
@@ -109,7 +112,9 @@ recv_from_to(int fd, void *buf, size_t len, int flags,
         struct iovec iov[1];
         union {
                 char cmsg[CMSG_SPACE(sizeof(struct in_pktinfo))];
+#if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
                 char cmsg6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
+#endif
         } u;
         struct cmsghdr *cmsgptr;
         struct msghdr msg;