Re: [PATCH] slab: Fix misplaced __free_one()

Randy Dunlap
2020-06-26T20:57:09Z

On 6/26/20 1:07 PM, Kees Cook wrote:
> The implementation of __free_one() was accidentally placed inside a
> CONFIG_NUMA #ifdef. Move it above.
>
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Link: https://lore.kernel.org/lkml/7ff248c7-d447-340c-a8e2-8c02972aca70@infradead.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested

Thanks.

> ---
> This a fix for slab-add-naive-detection-of-double-free.patch
> ---
> mm/slab.c | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index bbff6705ab2b..5ccb151a6e8f 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -588,6 +588,16 @@ static int transfer_objects(struct array_cache *to,
> return nr;
> }
>
> +/* &alien->lock must be held by alien callers. */
> +static __always_inline void __free_one(struct array_cache *ac, void *objp)
> +{
> + /* Avoid trivial double-free. */
> + if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) &&
> + WARN_ON_ONCE(ac->avail > 0 && ac->entry[ac->avail - 1] == objp))
> + return;
> + ac->entry[ac->avail++] = objp;
> +}
> +
> #ifndef CONFIG_NUMA
>
> #define drain_alien_cache(cachep, alien) do { } while (0)
> @@ -749,16 +759,6 @@ static void drain_alien_cache(struct kmem_cache *cachep,
> }
> }
>
> -/* &alien->lock must be held by alien callers. */
> -static __always_inline void __free_one(struct array_cache *ac, void *objp)
> -{
> - /* Avoid trivial double-free. */
> - if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) &&
> - WARN_ON_ONCE(ac->avail > 0 && ac->entry[ac->avail - 1] == objp))
> - return;
> - ac->entry[ac->avail++] = objp;
> -}
> -
> static int __cache_free_alien(struct kmem_cache *cachep, void *objp,
> int node, int page_node)
> {
>

--
~Randy