LD_PRELOAD potential problems

[dfs () DOE CARLETON CA (David F. Skoll)]

Many UNIX systems allow you to "pre-load" shared libraries by setting
an environment variable LD_PRELOAD.  This allows you to do interesting
things like replace standard C library functions or even the C
interfaces to system calls with your own functions.

I recently ran across a piece of software which depended upon knowing
the time reasonably accurately.  By replacing the time(2) UNIX system
call with my own function, I was able to fool the program and get it
to misbehave, without the inconvenience of actually changing the system
time or even requiring root privileges.

If you are writing programs which depend on C library functions or
UNIX system calls for secure operation, please distribute only
statically-linked versions, as the effort to fool statically-linked
binaries is a lot higher than a simple LD_PRELOAD spoof.

--
David F. Skoll
http://www.roaringpenguin.com