ipv6: honor IPV6_PKTINFO with v4 mapped addresses on sendmsg

In case we decide in udp6_sendmsg to send the packet down the ipv4
udp_sendmsg path because the destination is either of family AF_INET or
the destination is an ipv4 mapped ipv6 address, we don't honor the
maybe specified ipv4 mapped ipv6 address in IPV6_PKTINFO.

We simply can check for this option in ip_cmsg_send because no calls to
ipv6 module functions are needed to do so.

Reported-by: Gert Doering <gert@space.net>
Cc: Tore Anderson <tore@fud.no>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 1 deletions

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 580dd96666e0..0968b28c4cf3 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -186,7 +186,8 @@ void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(ip_cmsg_recv);
 
-int ip_cmsg_send(struct net *net, struct msghdr *msg, struct ipcm_cookie *ipc)
+int ip_cmsg_send(struct net *net, struct msghdr *msg, struct ipcm_cookie *ipc,
+                 bool allow_ipv6)
 {
         int err, val;
         struct cmsghdr *cmsg;
@@ -194,6 +195,22 @@ int ip_cmsg_send(struct net *net, struct msghdr *msg, struct ipcm_cookie *ipc)
         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg)) {
                 if (!CMSG_OK(msg, cmsg))
                         return -EINVAL;
+#if defined(CONFIG_IPV6)
+                if (allow_ipv6 &&
+                    cmsg->cmsg_level == SOL_IPV6 &&
+                    cmsg->cmsg_type == IPV6_PKTINFO) {
+                        struct in6_pktinfo *src_info;
+
+                        if (cmsg->cmsg_len < CMSG_LEN(sizeof(*src_info)))
+                                return -EINVAL;
+                        src_info = (struct in6_pktinfo *)CMSG_DATA(cmsg);
+                        if (!ipv6_addr_v4mapped(&src_info->ipi6_addr))
+                                return -EINVAL;
+                        ipc->oif = src_info->ipi6_ifindex;
+                        ipc->addr = src_info->ipi6_addr.s6_addr32[3];
+                        continue;
+                }
+#endif
                 if (cmsg->cmsg_level != SOL_IP)
                         continue;
                 switch (cmsg->cmsg_type) {