linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference in setup_kmem_cache

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Date:   Wed, 2 Jan 2019 17:01:20 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Christopher Lameter <cl@...ux.com>
Cc:     syzbot <syzbot+d6ed4ec679652b4fd4e4@...kaller.appspotmail.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        David Miller <davem@...emloft.net>,
        Eric Van Hensbergen <ericvh@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Latchesar Ionkov <lucho@...kov.net>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        v9fs-developer@...ts.sourceforge.net,
        Linux-MM <linux-mm@...ck.org>, Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference in setup_kmem_cache_node

On Wed, Jan 2, 2019 at 4:51 PM Christopher Lameter <cl@...ux.com> wrote:
>
> On Wed, 2 Jan 2019, Dmitry Vyukov wrote:
>
> > Am I missing something or __alloc_alien_cache misses check for
> > kmalloc_node result?
> >
> > static struct alien_cache *__alloc_alien_cache(int node, int entries,
> >                                                 int batch, gfp_t gfp)
> > {
> >         size_t memsize = sizeof(void *) * entries + sizeof(struct alien_cache);
> >         struct alien_cache *alc = NULL;
> >
> >         alc = kmalloc_node(memsize, gfp, node);
> >         init_arraycache(&alc->ac, entries, batch);
> >         spin_lock_init(&alc->lock);
> >         return alc;
> > }
> >
>
>
> True _alloc_alien_cache() needs to check for NULL
>
>
> From: Christoph Lameter <cl@...ux.com>
> Subject: slab: Alien caches must not be initialized if the allocation of the alien cache failed
>
> Callers of __alloc_alien() check for NULL.
> We must do the same check in __alloc_alien_cache to avoid NULL pointer dereferences
> on allocation failures.
>
> Signed-off-by: Christoph Lameter <cl@...ux.com>

Please add:
Reported-by: syzbot+d6ed4ec679652b4fd4e4@...kaller.appspotmail.com

> Index: linux/mm/slab.c
> ===================================================================
> --- linux.orig/mm/slab.c
> +++ linux/mm/slab.c
> @@ -666,8 +666,10 @@ static struct alien_cache *__alloc_alien
>         struct alien_cache *alc = NULL;
>
>         alc = kmalloc_node(memsize, gfp, node);
> -       init_arraycache(&alc->ac, entries, batch);
> -       spin_lock_init(&alc->lock);
> +       if (alc) {
> +               init_arraycache(&alc->ac, entries, batch);
> +               spin_lock_init(&alc->lock);
> +       }
>         return alc;
>  }
>