[Cocci] malloc/calloc/strup adding missing NULL checks

[thomas.adam22@gmail.com (Thomas Adam)]

On Fri, Dec 16, 2016 at 08:21:35PM +0100, Julia Lawall wrote:
> The problem for the vset function is that a pattern like
> 
> A
> ...
> 
> requires that there be no A along all paths leaving from the matched A.
> Your code matching the first pattern is in a loop, so obviously there is
> at least one path that reaches A again.  So the rule doesn't match.  If
> you want to consider the region until A optionally occurs again, then you
> can write:
> 
> A
> ...
> ?A
> 
> The ? makes it optional.

Ah.  I think I understand that, Julia.  If I blindly modify the strdup rule to
this:

	T = strdup(...);
	+ if (T == NULL)
	+ 	pkg_emit_errno("strdup", __func__);
	?... when != (T == NULL)
	?    when != (T != NULL)

And then run:

	spatch --in-place --sp-file ~/unchecked_malloc.cocci libpkg/pkg.c

This now captures the other remaining strdup() calls which were going
undetected.  However, as a side-effect of this, the matching rule is adding in
the same NULL checks for function calls which already has them; hence a
doubling-up.

I appreciate I've just blindly followed your advice; could you perhaps
elaborate (and educate me) as to the correct way to ammend this rule?

Thanks.

Thomas