gdb - debugging with piped input (not arguments) [duplicate]

Question

I typically run my program with:

perl -e 'print "A"x200' | ./vuln_prog

The stdin is consumed by a gets() function in C++.

If this were just a command argument, I could open gdb by doing:

gdb ./vuln_prog
run $(perl -e 'print "A"x200')

However, my scenario is not a command argument, but rather input (STDIN?). How would I debug this in gdb? I've tried a bunch of options, but nothing seems to really work.

I would normally just run gdb on the process, and when it prompts for user input, type it in, however I'm not wanting to type just "A". I want to type all chars from \x00-\xff, which I can't type.

Why are you using gets? I mean sometimes it's acceptable (like if you're just writing a quick program to test something, or if the program will only be run with trusted input) but I'm curious. — Sparkette
– Sparkette, Commented Sep 19, 2016 at 22:33
It was not my code. It was for a fun reverse engineering challenge, where the code was provided. — mandreko
– mandreko, Commented Sep 20, 2016 at 12:28
Oh okay. Was gets intentionally used because it was vulnerable, like as part of a possible solution to the challenge? — Sparkette
– Sparkette, Commented Sep 21, 2016 at 2:38
@flarn2006 Indeed it was the vulnerable function. I was able to do a buffer overflow due to it not bound-checking. — mandreko
– mandreko, Commented Sep 21, 2016 at 14:02
r < <(perl -e 'print "A"x200') (as the question is closed, not as answer) — thejonny
– thejonny, Commented May 6, 2019 at 20:07

zed_0xff · Accepted Answer · 2011-12-07 20:47:30Z

129

gdb ./vuln_prog
run < filename_with_input

answered Dec 7, 2011 at 20:47

zed_0xff

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10 Comments

Thomas Ahle Over a year ago

Does the have a lldb equivalent?

jernkuan Over a year ago

@ThomasAhle For lldb equivalent stackoverflow.com/questions/29861242/…

j13r Over a year ago

@iAdjunct I saw in another question that you can use the bash syntax, i.e., "run < <(bunzip file.bz2)"

Shinlos Over a year ago

is there any way to pipe without writing to file?

Josh Desmond Over a year ago

@Shinlos I'm still trying to figure out how this syntax works, but I believe, run < <(python3 ~/exploit.py) will work if you're trying to pipe in the output of exploit.py into the program you're currently stepping in gdb.

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