From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH] net: sk_prot_alloc() should not blindly overwrite memory Date: Thu, 9 Jul 2009 10:13:28 -0700 Message-ID: <20090709171328.GB6723@linux.vnet.ibm.com> References: <4A537469.3040207@gmail.com> <4A53CD39.7080407@gmail.com> <20090707.191424.167842005.davem@davemloft.net> <4A5441A0.3050504@gmail.com> <4A5581C5.5070409@gmail.com> Reply-To: paulmck@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: Eric Dumazet Return-path: Received: from e5.ny.us.ibm.com ([32.97.182.145]:58993 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752484AbZGIRNd (ORCPT ); Thu, 9 Jul 2009 13:13:33 -0400 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by e5.ny.us.ibm.com (8.13.1/8.13.1) with ESMTP id n69H6fm6013503 for ; Thu, 9 Jul 2009 13:06:41 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n69HDUA5255660 for ; Thu, 9 Jul 2009 13:13:30 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n69HDSXN001161 for ; Thu, 9 Jul 2009 13:13:30 -0400 Content-Disposition: inline In-Reply-To: <4A5581C5.5070409@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: 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 > >=20 > > Thanks David > >=20 > > I forgot to CC Paul and Patrick, so I'll ask them to look at this p= atch. > >=20 > > 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. > >=20 > >=20 > > Here is the patch again so that Paul & Patrick can comment on it. > >=20 > > 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. >=20 > Here is an updated and much simpler patch, taking care of sk_node.nex= t being not set to 0 >=20 > This patch applies to >=3D 2.6.29 kernels Does this one also need the rearrangement of struct elements in the earlier patch? (And apologies about being slow to get to that one.) Thanx, Paul > [PATCH] net: sk_prot_alloc() should not blindly overwrite memory >=20 > 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. >=20 > Current sk_prot_alloc() implementation doesnt respect this hypothesis= , > calling kmem_cache_alloc() with __GFP_ZERO. Just call memset() around > the forbidden field. >=20 > 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; >=20 > 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); >=20