[SOLVED] Overwrite bash string variable

Soderlund · 12-26-2015, 02:40 AM

Code:

read -p 'Password: ' -s password

How do I overwrite the $password variable in memory?

Is it possible to memset it?

berndbausch · 12-26-2015, 06:10 AM

You want to assign a different value to a variable? This is done as follows:

Code:

password=whatevervalueyouwanttosetitto

This includes the empty string:

Code:

password=""

You can also unset the variable:

Code:

unset password

When unset, attempting to access $password will result in an error.

Or do you need to do something else?

Soderlund · 12-26-2015, 07:18 AM

When you set a variable, it is stored in dynamically allocated memory (RAM or swap). I need to overwrite the bytes that the string used in memory. When you assign it another value or unset it, it is probably just freed, i.e. the memory is marked as "writable" but the string may still be there.

jpollard · 12-26-2015, 07:59 AM

Nope. Not going to happen. Every string is replicated during assignment, and the pre-existing string deallocated.

There is no "overwrite".

If you are actually doing secure coding, use C instead, you have the control over any storage used.