Briefly describe race conditions in file access.

Question

What will be an ideal response?

Answer 1

Race condition is a common attack exploit. In general, it is a where an attacker can "race in" and change something between two actions in your program. The goal is to make your program misbehave. As mentioned in the previous section, a common race condition arises when testing for file existence using code such as:

unless (-e $myfilename) # bad practice
{
open(FH, "> $myfilename");
}

In this case, there is a race between testing whether or not the file exists and opening it for writing. There is no guarantee that the answer returned by the -e test will still be valid by the time the open is called. An attacker can replace the file with a link to something important and cause the code to erase that file.