Project JEDI - Issue Tracker - JEDI VCL
Viewing Issue Advanced Details
6570 00 JVCL Components crash always 2017-05-08 15:43 2018-10-28 17:34
rarog  
 
normal  
feedback Daily / GIT  
open  
none    
none  
0006570: JvMemoryData easilly corrupts buffer when using many fields
TJvMemoryData.InitFieldDefsFromFields can easily corrupt the buffer without throwing any error.

The problem root is in this line:
Inc(Offset, CalcFieldLen(DataType, Size) + 1);

It just increases the offset without checking, if it causes a cycle getting an overflow when reaching values over 65535.

To reproduce it, it should be enough to load a data with 22 WideString fields. Each of them is initialised by default to hold 1500 chars, each char takes 2 bytes.
So 1500 * 2 * 22 = 66000 resulting in the buffer to be in between and corrupt memory.
Issue History
2017-05-08 15:43 rarog New Issue
2018-07-18 15:57 obones Note Added: 0021531
2018-07-18 15:57 obones Status new => feedback
2018-10-28 17:34 mh Note Added: 0021587

Notes
(0021531)
obones   
2018-07-18 15:57   
Could you check if the issue is still present in the latest GIT content? If yes, please provide the zipped sources of an application showing this.
(0021587)
mh   
2018-10-28 17:34   
In the current version this line mentioned seems to have been changed to this one:
Inc(Offset, CalcFieldLen(FieldDefList[I].DataType, FieldDefList[I].Size) + 1);

While it looks different is still doesn't check if the offset variable (which is a Word) overflows.

There should be a if before actually incrementing offset ensuring that it is only incremented when it won't overflow. In case of an overflow raising an exception might be appropriate.