Re: [BUG mm-unstable] BUG: KASAN: use-after-free in shrink_folio_list+0x9f4/0x1ae0

[Matthew Wilcox <willy@infradead.org>]

On Fri, Jul 07, 2023 at 02:12:06PM -0400, David Wysochanski wrote:
> I think myself / Daire Byrne may have already tracked this down and I
> found a 1-liner that fixed a similar crash in his environment.
> 
> Can you try this patch on top and let me know if it still crashes?
> https://github.com/DaveWysochanskiRH/kernel/commit/902c990e311120179fa5de99d68364b2947b79ec

Said one-liner:
-	struct address_space *mapping = folio->mapping;
+	struct address_space *mapping = folio_mapping(folio);

This will definitely fix the problem.  shrink_folio_list() sees
anonymous folios as well as file folios.

I wonder if we want to go a step further and introduce ...

+static inline bool __folio_needs_release(struct address_space *mapping,
+               struct folio *folio)
+{
+       return folio_has_private(folio) ||
+               (mapping && mapping_release_always(mapping));
+}
+
 /*
  * Return true if a folio needs ->release_folio() calling upon it.
  */
 static inline bool folio_needs_release(struct folio *folio)
 {
-       struct address_space *mapping = folio->mapping;
-
-       return folio_has_private(folio) ||
-               (mapping && mapping_release_always(mapping));
+       return __folio_needs_release(folio_mapping(folio), folio);
 }

since two of the three callers already have done the necessary dance to
get the mapping (and they're the two which happen regularly; the third
is an unusual situation).