The final routing for ipv4 packets may be done with the IP address
from the message header not that from the address buffer.
If the addresses are different FLOWI_FLAG_KNOWN_NH must be set so
that a temporary 'struct rtable' entry is created to send the message.
However the allocate + free (under RCU) is relatively expensive
and can be avoided by a quick check shows the addresses match.
Signed-off-by: David Laight <david.lai...@aculab.com>
---
This makes a considerable difference when we are sending a lot
of RTP streams from a raw socket.
IP_HDRINCL has to be set so that the calculated UDP checksum is right.
net/ipv4/raw.c | 30 ++++++++++++++++++++++++++++--
1 file changed, 28 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 3183413..0a81376 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -495,6 +495,27 @@ static int raw_getfrag(void *from, char *to, int offset,
int len, int odd,
return ip_generic_getfrag(rfv->msg, to, offset, len, odd, skb);
}
+static bool raw_msg_addr_matches(struct msghdr *msg, __be32 daddr)
+{
+ const struct iovec *iov;
+ __be32 msg_daddr;
+
+ /* Check common case of user buffer with header in the first fragment.
+ * If we return false the message is still sent.
+ */
+
+ if (!iter_is_iovec(&msg->msg_iter))
+ return false;
+ iov = msg->msg_iter.iov;
+ if (!iov || iov->iov_len < 20)
+ return false;
+
+ if (get_user(msg_daddr, (__be32 __user *)(iov->iov_base + 16)))
+ return false;
+
+ return daddr == msg_daddr;
+}
+
static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
struct inet_sock *inet = inet_sk(sk);
@@ -626,9 +647,14 @@ static int raw_sendmsg(struct sock *sk, struct msghdr
*msg, size_t len)
flowi4_init_output(&fl4, ipc.oif, ipc.sockc.mark, tos,
RT_SCOPE_UNIVERSE,
hdrincl ? IPPROTO_RAW : sk->sk_protocol,
- inet_sk_flowi_flags(sk) |
- (hdrincl ? FLOWI_FLAG_KNOWN_NH : 0),
+ inet_sk_flowi_flags(sk),
daddr, saddr, 0, 0, sk->sk_uid);
+ /* The final message routing may be done with the destination address
+ * in the user-supplied ipv4 header. If this differs from 'daddr' then
+ * a temporary destination table entry has to be created.
+ */
+ if (hdrincl && !raw_msg_addr_matches(msg, daddr))
+ fl4.flowi4_flags |= FLOWI_FLAG_KNOWN_NH;
if (!hdrincl) {
rfv.msg = msg;
--
1.8.1.2
-
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