Potential NULL dereference in pag.cpp?

[Mark Rotteveel]

Visual Studio warns about a possible NULL dereference in pag.cpp,
function PAG_release_pages. Specifically on line 1372, as pages could be
NULL if cntRelease <= 0.

I'm not sure if that can happen in practice, but the logic in some of
some of the callers is complicated enough that I cannot exclude the
possibility that it might be 0.

What would be the proper fix here? Add a guard clause at the function
start to return early if cntRelease <= 0? Or modify the condition on
line 1372 to
```
if (pages && pages->pip_extent < pageMgr.pagesPerPIP)
```
or something else?

Mark
--
Mark Rotteveel

[Vlad Khorsun]

07.08.2025 14:31, 'Mark Rotteveel' via firebird-devel:

> Visual Studio warns about a possible NULL dereference in pag.cpp, function PAG_release_pages. Specifically on line 1372, as pages
> could be NULL if cntRelease <= 0.
>
> I'm not sure if that can happen in practice, but the logic in some of some of the callers is complicated enough that I cannot
> exclude the possibility that it might be 0.

cntRelease is a number of pages to release. Of course, it must be > 0.

> What would be the proper fix here? Add a guard clause at the function start to return early if cntRelease <= 0?

Yes, it should be enough and should not harm performance.
And fb_assert() to catch such "impossible" case in DEBUG build, please.

Regards,
Vlad