mORMot Open Source

Magnus

Member

Registered: 2015-05-27

Posts: 2

Pointer arithmetic overflow.

Hi, just wanted to alert you to an problem around some pointer arithmetic.

I got an access violation and traced it to the method:

TPdfWrite.Add(Text: PAnsiChar; Len: integer): TPdfWrite;

The ultimate reason was the statement:

if B+Len>=Bend then begin

In my case

B = $FFF73C82 
Len = $A2CBA
B + Len = $1693C
Bend = $FFF73DD3

and the if statement evaluated to false and the buffer was not reallocated, leading to an access violation.

I change the code to

if Len >= Bend - B then begin

and the problem was avoided.

Regards,

/Magnus

ab

Administrator

From: France

Registered: 2010-06-21

Posts: 14,206

Website

Re: Pointer arithmetic overflow.

Why is the B pointer negative?
Is is due to http://en.wikipedia.org/wiki/Address_sp … domization ?
On which system? In which context?
I've never observed this until know.

I tried to fix such problem with TPdfWrite and also with TTextWriter (used e.g. for JSON creation or TSynLog).
See http://synopse.info/fossil/info/5ecb9f455b
But there may be other potential similar issues in our source code: any additional input is welcome!

Thanks for the feedback!