linux-kernel - slob: Check for NULL pointer before calling ctor()

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Message-ID: <1358442365.23211.17.camel@gandalf.local.home>
Date:	Thu, 17 Jan 2013 12:06:05 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...r.kernel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>
Subject: slob: Check for NULL pointer before calling ctor()

While doing some code inspection, I noticed that the slob constructor
method can be called with a NULL pointer. If memory is tight and slob
fails to allocate with slob_alloc() or slob_new_pages() it still calls
the ctor() method with a NULL pointer. Looking at the first ctor()
method I found, I noticed that it can not handle a NULL pointer (I'm
sure others probably can't either):

static void sighand_ctor(void *data)
{
        struct sighand_struct *sighand = data;

        spin_lock_init(&sighand->siglock);
        init_waitqueue_head(&sighand->signalfd_wqh);
}

The solution is to only call the ctor() method if allocation succeeded.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/mm/slob.c b/mm/slob.c
index a99fdf7..48fcb90 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -554,7 +554,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
 					    flags, node);
 	}
 
-	if (c->ctor)
+	if (b && c->ctor)
 		c->ctor(b);
 
 	kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);


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