Re: [PATCH] mm/z3fold.c: don't try to use buddy slots after free

[Shakeel Butt <shakeelb@google.com>]

On Mon, Jul 8, 2019 at 4:48 AM Vitaly Wool <vitalywool@gmail.com> wrote:
>
> From fd87fdc38ea195e5a694102a57bd4d59fc177433 Mon Sep 17 00:00:00 2001
> From: Vitaly Wool <vitalywool@gmail.com>
> Date: Mon, 8 Jul 2019 13:41:02 +0200
> [PATCH] mm/z3fold: don't try to use buddy slots after free
>
> As reported by Henry Burns:
>
> Running z3fold stress testing with address sanitization
> showed zhdr->slots was being used after it was freed.
>
> z3fold_free(z3fold_pool, handle)
>   free_handle(handle)
>     kmem_cache_free(pool->c_handle, zhdr->slots)
>   release_z3fold_page_locked_list(kref)
>     __release_z3fold_page(zhdr, true)
>       zhdr_to_pool(zhdr)
>         slots_to_pool(zhdr->slots)  *BOOM*
>
> To fix this, add pointer to the pool back to z3fold_header and modify
> zhdr_to_pool to return zhdr->pool.
>
> Fixes: 7c2b8baa61fe  ("mm/z3fold.c: add structure for buddy handles")
>
> Reported-by: Henry Burns <henryburns@google.com>
> Signed-off-by: Vitaly Wool <vitalywool@gmail.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>

> ---
>  mm/z3fold.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 985732c8b025..e1686bf6d689 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -101,6 +101,7 @@ struct z3fold_buddy_slots {
>   * @refcount:          reference count for the z3fold page
>   * @work:              work_struct for page layout optimization
>   * @slots:             pointer to the structure holding buddy slots
> + * @pool:              pointer to the containing pool
>   * @cpu:               CPU which this page "belongs" to
>   * @first_chunks:      the size of the first buddy in chunks, 0 if free
>   * @middle_chunks:     the size of the middle buddy in chunks, 0 if free
> @@ -114,6 +115,7 @@ struct z3fold_header {
>         struct kref refcount;
>         struct work_struct work;
>         struct z3fold_buddy_slots *slots;
> +       struct z3fold_pool *pool;
>         short cpu;
>         unsigned short first_chunks;
>         unsigned short middle_chunks;
> @@ -320,6 +322,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page,
>         zhdr->start_middle = 0;
>         zhdr->cpu = -1;
>         zhdr->slots = slots;
> +       zhdr->pool = pool;
>         INIT_LIST_HEAD(&zhdr->buddy);
>         INIT_WORK(&zhdr->work, compact_page_work);
>         return zhdr;
> @@ -426,7 +429,7 @@ static enum buddy handle_to_buddy(unsigned long handle)
>
>  static inline struct z3fold_pool *zhdr_to_pool(struct z3fold_header *zhdr)
>  {
> -       return slots_to_pool(zhdr->slots);
> +       return zhdr->pool;
>  }
>
>  static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
> --
> 2.17.1