| Message ID | 4A5581C5.5070409@gmail.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Thu, Jul 09, 2009 at 07:36:05AM +0200, Eric Dumazet wrote: > Eric Dumazet a écrit : > > David Miller a écrit : > >> From: Eric Dumazet <eric.dumazet@gmail.com> > >> 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 hypothesis, > >>> calling kmem_cache_alloc() with __GFP_ZERO and setting sk_refcnt to 1 > >>> instead of atomically increment it. > >>> > >>> Reported-by: Emil S Tantilov <emils.tantilov@gmail.com> > >>> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> > >> 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 patch. > > > > Patrick, a similar fix is needed in conntrack as well, we currently > > uses "ct = 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 > > atomic_inc_if_not_zero on it), but the nulls.next thing is problematic. > > Here is an updated and much simpler patch, taking care of sk_node.next being not set to 0 > > This patch applies to >= 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 > > 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 hypothesis, > calling kmem_cache_alloc() with __GFP_ZERO. Just call memset() around > the forbidden field. > > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> > --- > 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 = prot->slab; > - if (slab != NULL) > - sk = kmem_cache_alloc(slab, priority); > + if (slab != NULL) { > + sk = 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) != 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 = kmalloc(prot->obj_size, priority); > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Paul E. McKenney a écrit : > On Thu, Jul 09, 2009 at 07:36:05AM +0200, Eric Dumazet wrote: >> Eric Dumazet a écrit : >>> David Miller a écrit : >>>> From: Eric Dumazet <eric.dumazet@gmail.com> >>>> 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 hypothesis, >>>>> calling kmem_cache_alloc() with __GFP_ZERO and setting sk_refcnt to 1 >>>>> instead of atomically increment it. >>>>> >>>>> Reported-by: Emil S Tantilov <emils.tantilov@gmail.com> >>>>> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> >>>> 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 patch. >>> >>> Patrick, a similar fix is needed in conntrack as well, we currently >>> uses "ct = 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 >>> atomic_inc_if_not_zero on it), but the nulls.next thing is problematic. >> Here is an updated and much simpler patch, taking care of sk_node.next being not set to 0 >> >> This patch applies to >= 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.) > No, because only one field (sk_node.next) needs special attention, I felt it was not really necessary to reorder fields. First memset is inlined because of constant size, so small cost. Thanks > Thanx, Paul > >> [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 hypothesis, >> calling kmem_cache_alloc() with __GFP_ZERO. Just call memset() around >> the forbidden field. >> >> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> >> --- >> 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 = prot->slab; >> - if (slab != NULL) >> - sk = kmem_cache_alloc(slab, priority); >> + if (slab != NULL) { >> + sk = 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) != 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 = kmalloc(prot->obj_size, priority); >> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Thu, 09 Jul 2009 07:36:05 +0200 > [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 hypothesis, > calling kmem_cache_alloc() with __GFP_ZERO. Just call memset() around > the forbidden field. > > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> APplied and queued up for -stable. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
David Miller a écrit : > From: Eric Dumazet <eric.dumazet@gmail.com> > Date: Thu, 09 Jul 2009 07:36:05 +0200 > >> [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 hypothesis, >> calling kmem_cache_alloc() with __GFP_ZERO. Just call memset() around >> the forbidden field. >> >> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> > > APplied and queued up for -stable. I'll try to find some time to fix netfilter conntrack as well. Thanks -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 = prot->slab; - if (slab != NULL) - sk = kmem_cache_alloc(slab, priority); + if (slab != NULL) { + sk = 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) != 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 = kmalloc(prot->obj_size, priority);