Return-Path: Message-Id: <20120217005511.894980544@linuxfoundation.org> Date: Thu, 16 Feb 2012 16:55:24 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Zhihua Che , Eric Dumazet , Christoph Lameter , Pekka Enberg Subject: [15/15] slub: fix a possible memleak in __slab_alloc() In-Reply-To: <20120217005650.GA17119@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet commit 73736e0387ba0e6d2b703407b4d26168d31516a7 upstream. Zhihua Che reported a possible memleak in slub allocator on CONFIG_PREEMPT=y builds. It is possible current thread migrates right before disabling irqs in __slab_alloc(). We must check again c->freelist, and perform a normal allocation instead of scratching c->freelist. Many thanks to Zhihua Che for spotting this bug, introduced in 2.6.39 V2: Its also possible an IRQ freed one (or several) object(s) and populated c->freelist, so its not a CONFIG_PREEMPT only problem. Reported-by: Zhihua Che Signed-off-by: Eric Dumazet Acked-by: Christoph Lameter Signed-off-by: Pekka Enberg Signed-off-by: Greg Kroah-Hartman --- mm/slub.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/mm/slub.c +++ b/mm/slub.c @@ -1818,6 +1818,11 @@ static void *__slab_alloc(struct kmem_ca if (unlikely(!node_match(c, node))) goto another_slab; + /* must check again c->freelist in case of cpu migration or IRQ */ + object = c->freelist; + if (object) + goto update_freelist; + stat(s, ALLOC_REFILL); load_freelist: @@ -1827,6 +1832,7 @@ load_freelist: if (kmem_cache_debug(s)) goto debug; +update_freelist: c->freelist = get_freepointer(s, object); page->inuse = page->objects; page->freelist = NULL;