From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] net: sk_prot_alloc() should not blindly overwrite memory Date: Thu, 09 Jul 2009 22:50:00 +0200 Message-ID: <4A5657F8.5090205@gmail.com> References: <4A537469.3040207@gmail.com> <4A53CD39.7080407@gmail.com> <20090707.191424.167842005.davem@davemloft.net> <4A5441A0.3050504@gmail.com> <4A5581C5.5070409@gmail.com> <20090709171328.GB6723@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: David Miller , emil.s.tantilov@intel.com, emils.tantilov@gmail.com, netdev@vger.kernel.org, jesse.brandeburg@intel.com, jeffrey.t.kirsher@intel.com, jolsa@redhat.com, Patrick McHardy To: paulmck@linux.vnet.ibm.com Return-path: Received: from gw1.cosmosbay.com ([212.99.114.194]:48652 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754125AbZGIUuf (ORCPT ); Thu, 9 Jul 2009 16:50:35 -0400 In-Reply-To: <20090709171328.GB6723@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: Paul E. McKenney a =E9crit : > On Thu, Jul 09, 2009 at 07:36:05AM +0200, Eric Dumazet wrote: >> Eric Dumazet a =E9crit : >>> David Miller a =E9crit : >>>> From: Eric Dumazet >>>> Date: Wed, 08 Jul 2009 00:33:29 +0200 >>>> >>>>> [PATCH] net: sk_prot_alloc() should not blindly overwrite memory >>>>> >>>>> Some sockets use SLAB_DESTROY_BY_RCU, and our RCU code rely that = some >>>>> fields should not be blindly overwritten, even with null. >>>>> >>>>> These fields are sk->sk_refcnt and sk->sk_nulls_node.next >>>>> >>>>> Current sk_prot_alloc() implementation doesnt respect this hypoth= esis, >>>>> calling kmem_cache_alloc() with __GFP_ZERO and setting sk_refcnt = to 1 >>>>> instead of atomically increment it. >>>>> >>>>> Reported-by: Emil S Tantilov >>>>> Signed-off-by: Eric Dumazet >>>> I've applied this but will wait for some more testing before >>>> I push it out for real to kernel.org >>> Thanks David >>> >>> I forgot to CC Paul and Patrick, so I'll ask them to look at this p= atch. >>> >>> Patrick, a similar fix is needed in conntrack as well, we currently >>> uses "ct =3D kmem_cache_zalloc(nf_conntrack_cachep, gfp);" and thus >>> overwrite struct hlist_nulls_node hnnode; contained >>> in "struct nf_conntrack_tuple_hash", while lockless readers still >>> potentialy need them. Setting hnnode.next to NULL is dangerous >>> since last bit is not set (not a nulls value), a reader could >>> try to dereference this NULL pointer and trap. >>> >>> >>> Here is the patch again so that Paul & Patrick can comment on it. >>> >>> I am not sure about the refcnt thing (blindly setting it to 0 again >>> should be OK in fact, since no reader should/can to the=20 >>> atomic_inc_if_not_zero on it), but the nulls.next thing is problema= tic. >> Here is an updated and much simpler patch, taking care of sk_node.ne= xt being not set to 0 >> >> This patch applies to >=3D 2.6.29 kernels >=20 > Does this one also need the rearrangement of struct elements in the > earlier patch? (And apologies about being slow to get to that one.) >=20 No, because only one field (sk_node.next) needs special attention, I fe= lt it was not really necessary to reorder fields. First memset is inlined because of constant size, so small cost. Thanks > Thanx, Paul >=20 >> [PATCH] net: sk_prot_alloc() should not blindly overwrite memory >> >> Some sockets use SLAB_DESTROY_BY_RCU, and our RCU code correctness >> depends on sk->sk_nulls_node.next being always valid. A NULL >> value is not allowed as it might fault a lockless reader. >> >> Current sk_prot_alloc() implementation doesnt respect this hypothesi= s, >> calling kmem_cache_alloc() with __GFP_ZERO. Just call memset() aroun= d >> the forbidden field. >> >> Signed-off-by: Eric Dumazet >> --- >> diff --git a/net/core/sock.c b/net/core/sock.c >> index b0ba569..7b87ec0 100644 >> --- a/net/core/sock.c >> +++ b/net/core/sock.c >> @@ -939,8 +939,23 @@ static struct sock *sk_prot_alloc(struct proto = *prot, gfp_t priority, >> struct kmem_cache *slab; >> >> slab =3D prot->slab; >> - if (slab !=3D NULL) >> - sk =3D kmem_cache_alloc(slab, priority); >> + if (slab !=3D NULL) { >> + sk =3D kmem_cache_alloc(slab, priority & ~__GFP_ZERO); >> + if (!sk) >> + return sk; >> + if (priority & __GFP_ZERO) { >> + /* >> + * caches using SLAB_DESTROY_BY_RCU should let >> + * sk_node.next un-modified. Special care is taken >> + * when initializing object to zero. >> + */ >> + if (offsetof(struct sock, sk_node.next) !=3D 0) >> + memset(sk, 0, offsetof(struct sock, sk_node.next)); >> + memset(&sk->sk_node.pprev, 0, >> + prot->obj_size - offsetof(struct sock, >> + sk_node.pprev)); >> + } >> + } >> else >> sk =3D kmalloc(prot->obj_size, priority); >>