dccp: support for passing MSG_TRUNC

DCCP is datagram-oriented but lacks UDP's support for MSG_TRUNC as defined in
recvmsg(2)/recv(2). Hence the following 'Hello world\0' receiver

  len = recv(fd, buf, 10, MSG_PEEK | MSG_TRUNC);

wrongly (always) returns 10, while in UDP it returns 12 as expected.
This patch adds the missing MSG_TRUNC support to recvmsg().

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 671cd1413d59..85ec1cb7fd41 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -835,6 +835,8 @@ verify_sock_status:
                         len = -EFAULT;
                         break;
                 }
+                if (flags & MSG_TRUNC)
+                        len = skb->len;
         found_fin_ok:
                 if (!(flags & MSG_PEEK))
                         sk_eat_skb(sk, skb, 0);