Re: [PATCH v4 17/17] mm/sl[au]b: check if large object is valid in __ksize()

Vlastimil Babka
2022-08-23T17:34:19Z

On 8/17/22 12:18, Hyeonggon Yoo wrote:
> If address of large object is not beginning of folio or size of
> the folio is too small, it must be invalid. BUG() in such cases.
>
> Cc: Marco Elver <elver@google.com>
> Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> mm/slab_common.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 9c273a5fb0d7..98d029212682 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -984,8 +984,11 @@ size_t __ksize(const void *object)
>
> folio = virt_to_folio(object);
>
> - if (unlikely(!folio_test_slab(folio)))
> + if (unlikely(!folio_test_slab(folio))) {
> + BUG_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE);
> + BUG_ON(object != folio_address(folio));
> return folio_size(folio);
> + }
>
> return slab_ksize(folio_slab(folio)->slab_cache);
> }

In light of latest Linus' rant on BUG_ON() [1] I'm changing it to WARN_ON
and return 0, as it was in v3.

[1] https://lore.kernel.org/all/CAHk-=wiEAH+ojSpAgx_Ep=NKPWHU8AdO3V56BXcCsU97oYJ1EA@mail.gmail.com/

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 98d029212682..a80c3a5e194d 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -985,8 +985,10 @@ size_t __ksize(const void *object)
folio = virt_to_folio(object);

if (unlikely(!folio_test_slab(folio))) {
- BUG_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE);
- BUG_ON(object != folio_address(folio));
+ if (WARN_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE))
+ return 0;
+ if (WARN_ON(object != folio_address(folio)))
+ return 0;
return folio_size(folio);
}