Re: intercepting syscalls

Daniel Souza
2005-04-15T20:10:55Z

You're welcome, Igor. I needed to intercept syscalls in a little
project that I were implementing, to keep track of filesystem changes,
and others. I use that way, but I know that it's a ugly hack that can
work only under x86. Overwrite syscalls can slow down the whole
system, and a improper wrapper can freeze the system and behave in a
unexpected way (imagine a non-freed memory allocation in a sys_read
wrapper...), and others. I never planned to use it at production.

If you're trying to do something to be public and widely used, I
believe that a better approach is to create a layer to be used in
syscalls operations, or something like that (stills ugly, but now it's
a "good-programming-practice" thing).

For example, from a kernel to other, the way that sys_write works
internally may change, and your code can mess with the whole thing.
Trap system calls are not a portable and clean way to reach your
goals. In fact, there's not a reliable way yet. (that I know)

I agree that a mechanism to wrap system calls can be very useful.

--
# (perl -e "while (1) { print "\x90"; }") | dd of=/dev/evil