Full disclosure: I am seeking help to complete a college assignment. I am seeking help on steps where I am stuck and unable to move forward, not a ready made answer.
I need to exploit it to get a shell with the help of a shellcode through buffer overflow. The program has some check to avoid debugging and sort of canary to avoid buffer overflow. When I bypass these two checks, in gdb, I am able to get the shell.
However in the shell the program is exhibiting a behavior that I am not able to understand. When I attempt to pass a long string, instead of generating a segmentation fault the program suspends/stops.
$ ./prog $(python -c 'print "A" * 1000') + Stopped ./prog $(python -c 'print "A" * 1000')
Inside gdb, however, the program does generate segmentation fault. Similarly, inside gdb I am able to get a shell but in the shell the program stops/suspends like above. Attempting to bring it to foreground using 'fg' doesn't work and I do not get any respone. I have to kill it from another terminal.
$ file ./prog prog: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=7bfd429ec2e2d445afeb557b9eead176f3136690, not stripped
The output of ps when the program is stopped both due to my shellcode and by overflow:
$ ps f PID TTY STAT TIME COMMAND 3776 pts/0 Ss+ 0:39 -bash 17774 pts/0 t 0:00 \_ AAAAAAAAAAAAAAA.... 28834 pts/0 t 0:00 \_ /bin//sh
Can someone help me in understanding what syntax I should be looking for in the assembly code of this program to find what is causing the program to suspend? Or anything else I might be missing?