Out of bound checking leads to buffer overflow

[jlbirccyn]

Hi Michael

At lines https://github.com/madleech/ArduinoCMRI/blob/master/CMRI.cpp#L107, https://github.com/madleech/ArduinoCMRI/blob/master/CMRI.cpp#L115, https://github.com/madleech/ArduinoCMRI/blob/master/CMRI.cpp#L130, test should be >= to prevent out of bound access of the array.

Best regards

[Erik84750]

There seems to be no response, a pity.
Thank you for that correction, I modified manually.
Erik

[madleech]

Thanks for this, I've updated the code to fix the error. Not sure why I never encountered this during development.

[wizel10]

Hi,

I can confirm this bug. I've been struggling with the same issue - inputs above bit 16 never reaching JMRI.

The fix is on line 115 of CMRI.cpp. The bounds check:

if ((pos + 7) / 8 >= _tx_length)

should be:

if (pos / 8 >= _tx_length)

With the original code, bit 17 evaluates as (17+7)/8 = 3, which equals _tx_length (3 for 24 inputs),
so it returns false and the bit never gets sent.

With the fix, bit 17 evaluates as 17/8 = 2, which is less than 3, so it works correctly.

I tested this fix and can confirm bits 17-23 now work correctly.

Hope this helps and that the fix gets merged soon.