[asterisk-dev] [Code Review] 3356: Logic error in callerid checksum processing

[rmudgett]

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/branches/1.8/main/callerid.c
<https://reviewboard.asterisk.org/r/3356/#comment20841>

    I would be surprised if this worked for calls that the checksum was not zero.
    
    I think the expression should be:
    
    if ((b + cid->cksum) & 0xff)
    
    Otherwise you have a more likely overflow when the message bytes sum to larger than 8 bits.


- rmudgett


On March 14, 2014, 12:10 p.m., rmeyerriecks wrote:
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> (Updated March 14, 2014, 12:10 p.m.)
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> Review request for Asterisk Developers.
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> Bugs: asterisk-23488
>     https://issues.asterisk.org/jira/browse/asterisk-23488
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> Repository: Asterisk
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> Description
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> Callerid checksum-ing is being handled incorrectly here. When the checksum is calculated to be 0x00, it will perform 0x100-0x00 which results in 0x100. This value will then fail the otherwise correct callerid message. It was intended for devices on the rx side to simply add the calculated checksum to the transmitted 2's compliment checksum. A much simpler operation.
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> Diffs
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>   /branches/1.8/main/callerid.c 410575 
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> Diff: https://reviewboard.asterisk.org/r/3356/diff/
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> Testing
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> Thanks,
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> rmeyerriecks
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>

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