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From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
Date:   Sat, 30 Sep 2023 20:04:00 +0900
Message-ID: <CAB=+i9RQiDWE6ignfKn2p+UiDF9W=jAuqsmYhHrO9h06+X-pKA@mail.gmail.com>
Subject: Re: [RFC PATCH 01/14] mm/slub: don't try to dereference invalid freepointers
To:     Matteo Rizzo <matteorizzo@google.com>
Cc:     cl@linux.com, penberg@kernel.org, rientjes@google.com,
        iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz,
        roman.gushchin@linux.dev, keescook@chromium.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-mm@kvack.org, linux-hardening@vger.kernel.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
        corbet@lwn.net, luto@kernel.org, peterz@infradead.org,
        jannh@google.com, evn@google.com, poprdi@google.com,
        jordyzomer@google.com
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On Fri, Sep 15, 2023 at 7:59=E2=80=AFPM Matteo Rizzo <matteorizzo@google.co=
m> wrote:
>
> slab_free_freelist_hook tries to read a freelist pointer from the
> current object even when freeing a single object. This is invalid
> because single objects don't actually contain a freelist pointer when
> they're freed and the memory contains other data. This causes problems
> for checking the integrity of freelist in get_freepointer.
>
> Signed-off-by: Matteo Rizzo <matteorizzo@google.com>
> ---
>  mm/slub.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index f7940048138c..a7dae207c2d2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1820,7 +1820,9 @@ static inline bool slab_free_freelist_hook(struct k=
mem_cache *s,
>
>         do {
>                 object =3D next;
> -               next =3D get_freepointer(s, object);
> +               /* Single objects don't actually contain a freepointer */
> +               if (object !=3D old_tail)
> +                       next =3D get_freepointer(s, object);
>
>                 /* If object's reuse doesn't have to be delayed */
>                 if (!slab_free_hook(s, object, slab_want_init_on_free(s))=
) {
> --
> 2.42.0.459.ge4e396fd5e-goog
>

Looks good to me,
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>