Tech or Treat! Write an article about your scariest tech disaster to win gadgets!Learn more

x
?
Solved

Variable Overflow in UnixWare

Posted on 2000-03-18
1
Medium Priority
?
357 Views
Last Modified: 2013-12-05
I have been facing a very typical problem in SCO's Unixware. the following is a small example

memset(ovtm_row.offline_flg,'\0',2);
ovtm_row.offline_flg[0] ='N';
memset(ovtm_row.officer_id,'\0',3);
/**memset(ovtm_row.remarks,'\0',80);**/
 /*** Prev Line commented and Next line added to avoid INDEX Corruption in table odtr -Engineer Mon Dec 20 6:56:43 SST 1999 ***/
 memset(ovtm_row.remarks,'\0',30);
 memset(ovtm_row.auth_flg,'\0',2);
 if(sff != 1)
 ovtm_row.auth_flg[0] = 'Y';
 else
 ovtm_row.auth_flg[0] = 'N';
 }

In the above piece of code, there is a variable ovtm_row.remarks. This was initally declared as char(30). and at the time of initalisation it was filled with 80 chars. Here ideally, we were expecting a error, or atleast the program should have generated a core dump, segmentation fault. But instead, the program gets executed without any errors and is affecting the database table index, which is no where linked in the function.

My question is, Should the OS allow such overflowed variables to corrupt the database, and is it really the problem with the OS, or something else.
B'coz, after adding a single line where we are initalising the variable with 30 chars, the problem has been cleared.
0
Comment
Question by:vpotnis
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
1 Comment
 
LVL 40

Accepted Solution

by:
jlevie earned 200 total points
ID: 2631637
It's a problem with the code, not with the OS. In the general case the OS can't tell if a buffer is being over-run as the area is likely to just be somewhere within the region that the progamn does have write access to. The only times you'll get a core dump or memory protection violation are when the buffer over-run winds up writing over executable code and causes an invalid instruction trap, if it writes over a region that contains pointers, or if the write would extend beyond the address space of the program. Over writing pointers will cause all manner of grief, and depending on what pointers are over-written and when they are used the problem may not become apparent until much later in the execution of the program. Over-writing some other type of data region may just result in improper results.

There are tools to look for these sorts of problems at run time on a lot of operating systems (Rational's Purify for Sun, HP, & SGI; ParaSoft's Insure for Linux; ElectricFence on RedHat (at least); etc.) I don't know what's available for Unixware, you'd have to look.
0

Featured Post

[Webinar] Lessons on Recovering from Petya

Skyport is working hard to help customers recover from recent attacks, like the Petya worm. This work has brought to light some important lessons. New malware attacks like this can take down your entire environment. Learn from others mistakes on how to prevent Petya like worms.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

I have been running these systems for a few years now and I am just very happy with them.   I just wanted to share the manual that I have created for upgrades and other things.  Oooh yes! FreeBSD makes me happy (as a server), no maintenance and I al…
Using libpcap/Jpcap to capture and send packets on Solaris version (10/11) Library used: 1.      Libpcap (http://www.tcpdump.org) Version 1.2 2.      Jpcap(http://netresearch.ics.uci.edu/kfujii/Jpcap/doc/index.html) Version 0.6 Prerequisite: 1.      GCC …
Learn how to find files with the shell using the find and locate commands. Use locate to find a needle in a haystack.: With locate, check if the file still exists.: Use find to get the actual location of the file.:
This video shows how to set up a shell script to accept a positional parameter when called, pass that to a SQL script, accept the output from the statement back and then manipulate it in the Shell.
Suggested Courses

647 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question