From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Lameter Subject: Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from uninitialized memory in __alloc_skb Date: Tue, 10 May 2011 12:43:28 -0500 (CDT) Message-ID: References: <1303183217.4152.49.camel@edumazet-laptop> <1303244270.2756.3.camel@edumazet-laptop> <4DAE901C.2090809@cs.helsinki.fi> <1303286998.3186.18.camel@edumazet-laptop> <1303290464.3186.32.camel@edumazet-laptop> <1303293765.3186.74.camel@edumazet-laptop> <1303309591.3186.84.camel@edumazet-laptop> <1303311687.3186.100.camel@edumazet-laptop> <1305016988.2614.6.camel@edumazet-laptop> <4DC90D7D.9030808@cs.helsinki.fi> <1305022632.2614.18.camel@edumazet-laptop> <4DC91137.4030109@cs.helsinki.fi> <1305047682.2758.1.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII Cc: Vegard Nossum , Pekka Enberg , casteyde.christian@free.fr, Andrew Morton , netdev@vger.kernel.org, bugzilla-daemon@bugzilla.kernel.org, bugme-daemon@bugzilla.kernel.org To: Eric Dumazet Return-path: Received: from smtp101.prem.mail.ac4.yahoo.com ([76.13.13.40]:44432 "HELO smtp101.prem.mail.ac4.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750775Ab1EJRnc (ORCPT ); Tue, 10 May 2011 13:43:32 -0400 In-Reply-To: Content-ID: Sender: netdev-owner@vger.kernel.org List-ID: Draft for a patch Subject: slub: Make CONFIG_PAGE_ALLOC work with new fastpath Fastpath can do a speculative access to a page that CONFIG_PAGE_ALLOC may have marked as invalid to retrieve the pointer to the next free object. Probe that address before dereferencing the pointer to the page. All of that needs to occur with interrupts disabled since an interrupt could cause the page status to change (as pointed out by Eric). Signed-off-by: Christoph Lameter --- mm/slub.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) Index: linux-2.6/mm/slub.c =================================================================== --- linux-2.6.orig/mm/slub.c 2011-05-10 12:35:30.000000000 -0500 +++ linux-2.6/mm/slub.c 2011-05-10 12:38:53.000000000 -0500 @@ -261,6 +261,27 @@ static inline void *get_freepointer(stru return *(void **)(object + s->offset); } +static inline void *get_freepointer_safe(struct kmem_cache *s, void *object) +{ + void *p; + +#ifdef CONFIG_PAGE_ALLOC + unsigned long flags; + + local_irq_save(flags); + + if (probe_kernel_address(object)) + p = NULL; /* Invalid */ + else + p = get_freepointer(s, object); + + local_irq_restore(flags); +#else + p = get_freepointer(s, object); +#endif + return p; +} + static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) { *(void **)(object + s->offset) = fp; @@ -1933,7 +1954,7 @@ redo: if (unlikely(!irqsafe_cpu_cmpxchg_double( s->cpu_slab->freelist, s->cpu_slab->tid, object, tid, - get_freepointer(s, object), next_tid(tid)))) { + get_freepointer_safe(s, object), next_tid(tid)))) { note_cmpxchg_failure("slab_alloc", s, tid); goto redo;