From: Eric Dumazet <edumazet@google.com>

On Tue, 2012-10-30 at 09:58 +0100, Steven Barth wrote:

Hi,

I recently noticed that there might be an unexpected behavior in the 
handling of IPV6_PKTINFO for RAW-sockets. It seems that the given 
destination interface is ignored.

I just reproduced this on 3.7.0-rc3 vanilla but some quick tests with 
2.6.32 and 3.5 distro-kernels on different machines showed the same.

I've noticed this first in my own software but I could also reproduce it 
easily with standard tools like ping6 from iputils:

Have 2 network interfaces with (global) IPv6-addresses assigned (e.g. 
eth0 with fd00::1/64 and eth1 with fd01::1/64) and do a ping6 -I eth1 
fd00::1 (ping6 from iputils uses IPV6_PKTINFO internally).

For me the result was that even though I set the interface to eth1 the 
ECHO was still send to eth0.

Also (although probably unrelated) forwarding for IPv6 was disabled.

If I try something similar with IPv4 and ping -I ... the ECHO doesn't go 
out on eth0 but - as expected - on eth1.

However if I use traceroute(6) with -I (ICMP-traceroute) and the -i 
option to determine the interface, packages seem to be sent through the 
expected interface. Internally it seems that traceroute(6) uses 
SO_BINDTODEVICE instead of IP(V6)_PKTINFO which seems to work.

So it seems there might be something wrong with IPV6_PKTINFO or is this 
expected behavior?

I believe its not expected behavior.

Is the following patch fixing it ?

Thanks

[PATCH] ipv6: raw: honor IPV6_PKTINFO 

Let ping6 -I interface works correctly.

If socket was not bound to a given interface, check if IPV6_PKTINFO was
issued on this socket.

Reported-by: Steven Barth <redacted>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index d8e95c7..363ee65 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c

@@ -814,8 +814,8 @@ static int rawv6_sendmsg(struct kiocb *iocb, struct sock *sk,
 		fl6.flowlabel = np->flow_label;
 	}
 
-	if (fl6.flowi6_oif == 0)
-		fl6.flowi6_oif = sk->sk_bound_dev_if;
+	if (!fl6.flowi6_oif)
+		fl6.flowi6_oif = sk->sk_bound_dev_if ?: np->sticky_pktinfo.ipi6_ifindex;
 
 	if (msg->msg_controllen) {
 		opt = &opt_space;