[asterisk-dev] [Code Review] Resolve Sequence Number Rollover causing codec increase in res_rtp_multicast

[wdoekes]

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/branches/1.8/res/res_rtp_multicast.c
<https://reviewboard.asterisk.org/r/1542/#comment8778>

    I'd rather see something like this:
    
    put_unaligned_uint32(...(multicast->seqno & 0xFFFF)...
    
    This clarifies that we're dealing with 16 bits in the 32 bit int.
    
    And then simply do += 1 below, without any ANDing.
    
    P.S. The 0 << 23 still looks odd. If you're going to keep it, consider moving it between 30 and 16.


- wdoekes


On Oct. 27, 2011, 12:44 p.m., jrose wrote:
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> (Updated Oct. 27, 2011, 12:44 p.m.)
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> Review request for Asterisk Developers.
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> Summary
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> Basically what was happening was the sequence number would go above 65535, and rather than rolling back to zero, the extra bits would overflow into the codec bits of the RTP packet.  Because of this, if the sequence number goes above 65535, it'll make the codec value change and this can make calls fail.
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> This patch simply checks the value of the sequence number each time it is incremented and sets it back to 0 if it's above 65535.  Shouldn't cause any problems.
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> This addresses bug ASTERISK-18291.
>     https://issues.asterisk.org/jira/browse/ASTERISK-18291
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> Diffs
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>   /branches/1.8/res/res_rtp_multicast.c 341429 
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> Diff: https://reviewboard.asterisk.org/r/1542/diff
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> Testing
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> I checked the unpatched version with wireshark to make sure the codec shift was in fact happening and it was.  I checked it again after patching and made sure the problem went away and it did.  I also checked to see whether the values stayed as expected if I forcibly changed the codec value to something other than 0, and in all cases it behaved as expected.
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> Thanks,
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> jrose
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