[Freeswitch-users] Invalid length field in RTCP Sender Report

[Ken Rice]

This sort of thing should be reported via Jira ( http://jira.freeswitch.org
) will any logs, and patches attached...


On 9/24/12 11:00 AM, "James Bravo" <james.bravo at redmatter.com> wrote:

>    Hi
>  
>  We've had a number of Yealink T22 & T28 phones with later
>  firmware crashing within approx 30 seconds of sending
>  and receiving RTP.
>  Yealink R&D department have narrowed it down to a
>  non-standard RTCP 'Sender Report' packet from FreeSWITCH.
>  For some packet content, the length field in these packets
>  does not seem to agree with the overall UDP packet size.
>  RFC1889 defines the length as:
>      "The length of this RTCP packet in 32-bit words minus one,
>      including the header and any padding."
>  For instance, below is a RTCP packet sent from FS as viewed
>  in Wireshark. The length field says 76 bytes but the udp packet
>  length is 78 bytes so the last two bytes (0x31, 0x00) are excluded
>  as far as the length field is concerned.
>  
>  
>  I managed to stop the phones crashing by changing the following lines
>  in switch_rtp.c...
>          rtcp_bytes = sizeof(switch_rtcp_hdr_t) + sizeof(struct
> switch_rtcp_senderinfo) + sr->sr_desc_ssrc.length -1 ;
>          rtp_session->rtcp_send_msg.header.length = htons((u_short)(rtcp_bytes
> / 4) - 1); 
>  ...to something like...
>      {
>          switch_size_t rtcp_bytes_mod4;
>          rtcp_bytes = sizeof(switch_rtcp_hdr_t) + sizeof(struct
> switch_rtcp_senderinfo) + sr->sr_desc_ssrc.length -1 ;
>          // Add padding and adjust length if necessary
>          rtcp_bytes_mod4 = rtcp_bytes % 4;
>          if (rtcp_bytes_mod4 > 0)
>              rtcp_bytes += 4 - rtcp_bytes_mod4;
>          rtp_session->rtcp_send_msg.header.length = htons((u_short)(rtcp_bytes
> / 4 - 1)); 
>      }
>  although Freeswitch developers will probably find a better solution.
>  
>  Thanks in advance,
>  James Bravo, 
>  Redmatter
>  
>  
> 
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> 
> 
> 
> 
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-- 
Ken
http://www.FreeSWITCH.org
http://www.ClueCon.com
http://www.OSTAG.org
irc.freenode.net #freeswitch

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