linux-kernel - Re: [PATCH v2] mm/slub: Fix incorrect interpretation of s->offset

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Date:   Mon, 27 Apr 2020 16:10:31 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Waiman Long <longman@...hat.com>
cc:     Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Changbin Du <changbin.du@...il.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2] mm/slub: Fix incorrect interpretation of s->offset

On Mon, 27 Apr 2020, Waiman Long wrote:

>
> To fix it, use the check "s->offset == s->inuse" in the new helper
> function freeptr_after_object() instead. Also add another helper function
> get_info_end() to return the end of info block (inuse + free pointer
> if not overlapping with object).
>
> Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object")
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  mm/slub.c | 37 ++++++++++++++++++++++---------------
>  1 file changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 0e736d66bb42..68f1b4b1c309 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -551,15 +551,29 @@ static void print_section(char *level, char *text, u8 *addr,
>  	metadata_access_disable();
>  }
>
> +static inline bool freeptr_after_object(struct kmem_cache *s)

bool freeptr_outside_of_object()?

> +{
> +	return s->offset == s->inuse;

s->offset >= s->inuse?

There may be a redzone after the object.


> +static inline unsigned int get_info_end(struct kmem_cache *s)

static inline track_offset()?