Controlling processes and what to "feed" other processes



alsa-driver has a slight error in its Makefile.
The line in question is this here:

install -m 644 -g root -o root $f /usr/include/sound

Obviously it uses a specific name “root”, rather than the
number 0.

On systems which do not have a superuser name called root,
this will produce such an error:

install: invalid user `root’

Now, it is trivial to fix it (use numbers instead of fixed
names like “root”, because the numbers always work. To
reproduce sometimes odd behaviour you could alias root
to another name, like in:

usermod -l new_name root

But - since I am using ruby scripts for fetching source and
compiling it already, i wondered if there was a way to completely
control processes like the above.
In other words, my “watchguard” script would first check if a
command is valid, before it tries to execute it (or feed to make,
or some other binary).

In the above example it would simply change:

install -m 644 -g root -o root $f /usr/include/sound


install -m 644 -g 0 -o 0 $f /usr/include/sound

This seems like a trivial thing to do, although I have no
real idea how to do this at all.

PS: I already have a somewhat buggyruby script which actually
fixes incorrect Makefiles, but I thought that a ruby script
which can actually sanitize the input “on-the-fly” and correct
mistakes would be smarter and more powerful. So I am at
least in theory curious how to approach this problem.


On 24.05.2009 18:59, Marc H. wrote:

mistakes would be smarter and more powerful. So I am at
least in theory curious how to approach this problem.

For full control you would have to intercept system calls because you
would need to manipulate files while they are read. It might be
feasible but that would certainly very OS specific and it might not work
on all operating systems.

If you know that all programs are started via a shell you could try to
modify environment variable SHELL to point to a specific program which
would be able to interpret the general syntax of the shell you are using
and could identify files via their names (e.g. Makefile) and then do
some manipulations. However, that approach is not without issues and
you will certainly not be able to make it bullet proof.

Yet another solution: replace “make” with something you have written or
at least have control over and which treats “root” properly.

I’m curios what others will come up with.

Kind regards