Re: [PATCH] pseudo: fix memory leak and missed privilege drop

[Peter Seebach <peter.seebach@windriver.com>]

On Sun, 25 Aug 2013 19:40:06 -0500
"Peter A. Bigot" <pab@pabigot.com> wrote:

> qemu.bbclass adds PSEUDO_UNLOAD=1 in qemu_run_binary to avoid reference to
> pseudo functions that may not exist in the target environment.  This patch
> detects the addition of that variable within the environment to which the
> call applies, even if not present in the parent environment.
> 
> As a side effect it fixes a memory leak.

The memory leak was quasi-intentional -- I was aware of it, but I felt that
freeing memory right before an exec() was probably silly.

I'm currently waffling on a design question: It's obvious that, if execve()
has PSEUDO_UNLOAD=1 in envp, we want pseudo to be unloaded.

What if execve() doesn't have PSEUDO_UNLOAD=1, but some other thing has
happened which caused PSEUDO_UNLOAD to be 1 in the process that's calling
execve(), but which had not yet resulted in pseudo being unloaded? For
instance, I think there's at least one thing (memory is weak today, so I
can't remember at all where, but I think it might have been one of the Python
popen()-relatives) which lets you specify an environment, and if you do, that
is the *entire* environment -- it does not inherit.

My intuition is that if PSEUDO_UNLOAD is 1 in *either* of these, that should
win. But then we want a way to say "no, really, don't unload pseudo", which
means I might need to check for something like PSEUDO_UNLOAD=0 in envp.

So my proposed logic would be:

* if envp contains a value for PSEUDO_UNLOAD, act according to that value
* otherwise if pseudo_get_value("PSEUDO_UNLOAD") exists, use that
* otherwise act as though PSEUDO_UNLOAD is not set

(Where "is not set" implies "make sure pseudo's environment variables are
all present and expected to work.)

... But all of this is secondary. I think we should put this patch in-tree
for now so we can have the bug go away, and I can then spend a while
navel-gazing and deciding what should go into the official pseudo tree, which
is currently in a state of disrepair. Excellent catch!

-s
-- 
Listen, get this.  Nobody with a good compiler needs to be justified.