net: implement IP_RECVTOS for IP_PKTOPTIONS

Currently, it is not easily possible to get TOS/DSCP value of packets from
an incoming TCP stream. The mechanism is there, IP_PKTOPTIONS getsockopt
with IP_RECVTOS set, the same way as incoming TTL can be queried. This is
not actually implemented for TOS, though.

This patch adds this functionality, both for IPv4 (IP_PKTOPTIONS) and IPv6
(IPV6_2292PKTOPTIONS). For IPv4, like in the IP_RECVTTL case, the value of
the TOS field is stored from the other party's ACK.

This is needed for proxies which require DSCP transparency. One such example
is at http://zph.bratcheda.org/.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 0 deletions

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 9125529dab95..ca50d9f9f8c1 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1289,6 +1289,10 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
                         int hlim = inet->mc_ttl;
                         put_cmsg(&msg, SOL_IP, IP_TTL, sizeof(hlim), &hlim);
                 }
+                if (inet->cmsg_flags & IP_CMSG_TOS) {
+                        int tos = inet->rcv_tos;
+                        put_cmsg(&msg, SOL_IP, IP_TOS, sizeof(tos), &tos);
+                }
                 len -= msg.msg_controllen;
                 return put_user(len, optlen);
         }