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

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Date:   Wed, 2 Jan 2019 15:51:12 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Dmitry Vyukov <dvyukov@...gle.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, 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>


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;
 }