[asterisk-ss7] A fix to libss7 bug in SAM construction!

[Attila Domjan]

Hi,
which libss7 version are you looked into, I'm using mine and have tons
of incomming calls with SAM.
regards,
Attila

On Tue, 2009-10-20 at 20:32 +0800, Tian wrote:
> Hi guys,
> 
> I am reading libss7 source code and I think I've found a bug in it, 
> following is my description of the bug and my tentative fix to the bug, as I 
> don't have a running Asterisk box, I hope you will kindly help me check it, 
> thanks!
> 
> According to ITU-T Recommendation Q.763, section 1.6 'Mandatory variable 
> part':
> 
> "A pointer is also included to indicate the beginning of the optional part. 
> If the message type indicates that no optional part is allowed, then this 
> pointer will not be present. If the message type indicates that an optional 
> part is possible, but there is no optional part included in this particular 
> message, then a pointer field containing all zeros will be used."
> 
> Thus, ISUP messages that don't carry any optionals fall into two categories: 
> 1) those include a 'Pointer to start of optional part' containing all zeros 
> (e.g., SAM falls into this category) and 2) those don't include a 'Pointer 
> to start of optional part'.
> 
> libss7 can only correctly construct ISUP messages carrying zero optional 
> parameters that fall into category 2) if messages that fall into category 1) 
> are to be constructed, libss7 will fail.
> 
> The bug shows up in the file isup.c (Libss7 trunk revison 272, lines 
> 2425-2432), my fix to this bug specifically for SAM is as follows (you may 
> adopt the fix by replacing everyting between the fisrt and the last two 
> comment lines):
> 
>     /* Make sure we grab our opional parameters */
>     if (optparams || (messagetype == ISUP_SAM)) {
>         if (optparams)
>             opt_ptr = &mh->data[offset + varparams];
>         /* a SAM message doesn't have any optionals,
>          * but the 'Pointer to start of optional part' is still present
>          */
>         offset += varparams + 1; /* add one for the optionals */
>         len -= varparams + 1;
>     } else {
>         offset += varparams;
>         len -= varparams;
>     }
> 
>     /* Whew, some complicated math for all of these offsets and different 
> sections */
>  
> 
> 
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