Had a quick glance and your code is littered with unchecked function calls and potential overflows.
Also: Cookie:../../../<filename>
Where <filename> is a file starting with a value that's interpreted as a valid uid by atoi(). You're saved by a NULL pointer deref when the unchecked getpwuid() fails if the resulting uid is >0 but invalid (unless you're running it on a system where NULL is mapped to readable memory).
Also: Cookie:../../../<filename>
Where <filename> is a file starting with a value that's interpreted as a valid uid by atoi(). You're saved by a NULL pointer deref when the unchecked getpwuid() fails if the resulting uid is >0 but invalid (unless you're running it on a system where NULL is mapped to readable memory).