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

[rmeyerriecks]

> On March 14, 2014, 6:18 p.m., rmudgett wrote:
> > /branches/1.8/main/callerid.c, line 624
> > <https://reviewboard.asterisk.org/r/3356/diff/1/?file=56016#file56016line624>
> >
> >     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.

The "b" variable already has prior logic that decides to mask its lower 8 bits or not. I did it this way to maintain CID failure in the case of bit 8 or bit 9 being set by fsk_modem. Your line would ignore both those errors.

Granted, I could see the argument that we should probably try to pass CID even in the case that we get checksum errors, but I was just trying to follow the code convention.


- rmeyerriecks


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On March 14, 2014, 5:10 p.m., rmeyerriecks wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/3356/
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> 
> (Updated March 14, 2014, 5:10 p.m.)
> 
> 
> Review request for Asterisk Developers.
> 
> 
> Bugs: asterisk-23488
>     https://issues.asterisk.org/jira/browse/asterisk-23488
> 
> 
> Repository: Asterisk
> 
> 
> Description
> -------
> 
> 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.
> 
> 
> Diffs
> -----
> 
>   /branches/1.8/main/callerid.c 410575 
> 
> Diff: https://reviewboard.asterisk.org/r/3356/diff/
> 
> 
> Testing
> -------
> 
> 
> Thanks,
> 
> rmeyerriecks
> 
>

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