Python - Setting / Getting Environment Variables and Addrs

Question

I need to set an environment variable in Python and find the address in memory where it is located. Since it's on Linux, I don't mind about using libraries that only work consistently on Linux (if that's the only way). How would you do this?

Edit: The scope of the problem is as follows: I'm trying to hack a program for class, and essentially I'm putting my shellcode into an environment variable and then overwriting one byte on the victim code with the address of my environment variable. I need to find a way to automate this in Python, so my question is two-fold:

• Is there a way to get the address in memory of an environment variable?

• Can this only be done in bash/C or can I do it purely in Python?

Solution 1

The built in function id() returns a unique id for any object, which just happens to be it's memory address.

http://docs.python.org/library/functions.html#id

Solution 2

For accessing and setting environment variables, read up on the os.environ dictionary. You can also use os.putenv to set an environment variable.

Comments

[Russell Smith]

I realize this question was accepted but I don't see how it answers the root problem, namely "I need to set an environment variable in python". How will depending on the id returning a memory address solve the problem?

[JimB]

I assumed he was referring to python variables, only because the "the memory address" of a shell environment variable doesn't really make sense.

[tkokoszka]

I actually needed a way to get the memory address of where the shell environment variable is so I can feed it to a different program, which you can do with getenv() in C.

[JimB]

I'm a little confused - even in c, getenv only returns a string. char * getenv (const char *name)

[Ali Afshar]

Can't you just send a copy of the string to the "different program", do you really need the address?

[tkokoszka]

Yes, I'm trying to hack a program for class, and essentially I'm putting my shellcode into an environment variable and then overwriting one byte on the victim code with the address of my environment variable. But I need to find a way to automate this in Python, hence this question.

[tkokoszka]

@Jim: getenv returns a char*, which you can cast to void* and then print to see the memory location where the env var is.

[JimB]

Ok, I just thought there was a strcopy going on (I don't do a lot of C though). I wouldn't have guessed that the string in python's os.environ dict points to the actual char * in the environment though.

[tkokoszka]

From looking it over, it seems like it actually doesn't. It points to the Python representation, but I had accepted your answer because it looks like I can use it for a different purpose and it is technically correct.