Patchwork netfilter conntrack helper: nf_ct_h323: fix bug in rtcp natting

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Submitter Jagdish Motwani
Date May 22, 2012, 6 a.m.
Message ID <4FBB2B7B.6060907@elitecore.com>
Download mbox | patch
Permalink /patch/160542/
State Superseded
Headers show

Comments

Jagdish Motwani - May 22, 2012, 6 a.m.
The nat_rtp_rtcp hook takes two separate parameters port and rtp_port.

port is expected to be the real h245 address(found inside the packet).
rtp_port is the even number closest to port  (RTP ports are even and 
RTCP ports are odd)

However currently, both port and rtp_port are having same value(both are 
rounded to nearest even numbers).

This works well in case of openlogicalchannel with media (RTP/even) port.

But in case of openlogicalchannel for media control (RTCP/odd) port, 
h245 address in the packet is wrongly modified to have an even port.

I am attaching a pcap demonstrating the problem, for any further analysis.

This behavior was introduced around v2.6.19 while rewriting the helper.



Signed-off-by: Jagdish Motwani <jagdish.motwani@elitecore.com>
Signed-off-by: Sanket Shah <sanket.shah@elitecore.com>

--
         if ((rtp_exp = nf_ct_expect_alloc(ct)) == NULL)
Eric Dumazet - May 22, 2012, 6:28 a.m.
On Tue, 2012-05-22 at 11:30 +0530, Jagdish Motwani wrote:
> The nat_rtp_rtcp hook takes two separate parameters port and rtp_port.
> 
> port is expected to be the real h245 address(found inside the packet).
> rtp_port is the even number closest to port  (RTP ports are even and 
> RTCP ports are odd)
> 
> However currently, both port and rtp_port are having same value(both are 
> rounded to nearest even numbers).
> 
> This works well in case of openlogicalchannel with media (RTP/even) port.
> 
> But in case of openlogicalchannel for media control (RTCP/odd) port, 
> h245 address in the packet is wrongly modified to have an even port.
> 
> I am attaching a pcap demonstrating the problem, for any further analysis.
> 
> This behavior was introduced around v2.6.19 while rewriting the helper.
> 
> 
> 
> Signed-off-by: Jagdish Motwani <jagdish.motwani@elitecore.com>
> Signed-off-by: Sanket Shah <sanket.shah@elitecore.com>
> 
> --
> diff --git a/net/netfilter/nf_conntrack_h323_main.c 
> b/net/netfilter/nf_conntrack_h323_main.c
> index 46d69d7..7f0de36 100644
> --- a/net/netfilter/nf_conntrack_h323_main.c
> +++ b/net/netfilter/nf_conntrack_h323_main.c
> @@ -270,9 +270,8 @@ static int expect_rtp_rtcp(struct sk_buff *skb, 
> struct nf_conn *ct,
>                  return 0;
> 
>          /* RTP port is even */
> -       port &= htons(~1);
> -       rtp_port = port;
> -       rtcp_port = htons(ntohs(port) + 1);
> +       rtp_port = port & htons(~1);
> +       rtcp_port = htons(ntohs(rtp_port) + 1);

seems better to use :

rtp_port = port & ~htons(1);
rtcp_port = port | htons(1);



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Patch

diff --git a/net/netfilter/nf_conntrack_h323_main.c 
b/net/netfilter/nf_conntrack_h323_main.c
index 46d69d7..7f0de36 100644
--- a/net/netfilter/nf_conntrack_h323_main.c
+++ b/net/netfilter/nf_conntrack_h323_main.c
@@ -270,9 +270,8 @@  static int expect_rtp_rtcp(struct sk_buff *skb, 
struct nf_conn *ct,
                 return 0;

         /* RTP port is even */
-       port &= htons(~1);
-       rtp_port = port;
-       rtcp_port = htons(ntohs(port) + 1);
+       rtp_port = port & htons(~1);
+       rtcp_port = htons(ntohs(rtp_port) + 1);

         /* Create expect for RTP */