| Message ID | 20090723141533.19029.28754.sendpatchset@x2.localnet |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
On Thu, Jul 23, 2009 at 04:15:34PM +0200, Patrick McHardy wrote: > commit 2b12e9634d9676c55f576195a7f950956179d881 > Author: Patrick McHardy <kaber@trash.net> > Date: Thu Jul 23 16:02:18 2009 +0200 > > netfilter: nf_conntrack: nf_conntrack_alloc() fixes > > Upstream commit 941297f4: > > When a slab cache uses SLAB_DESTROY_BY_RCU, we must be careful when allocating > objects, since slab allocator could give a freed object still used by lockless > readers. > > In particular, nf_conntrack RCU lookups rely on ct->tuplehash[xxx].hnnode.next > being always valid (ie containing a valid 'nulls' value, or a valid pointer to next > object in hash chain.) > > kmem_cache_zalloc() setups object with NULL values, but a NULL value is not valid > for ct->tuplehash[xxx].hnnode.next. > > Fix is to call kmem_cache_alloc() and do the zeroing ourself. > > As spotted by Patrick, we also need to make sure lookup keys are committed to > memory before setting refcount to 1, or a lockless reader could get a reference > on the old version of the object. Its key re-check could then pass the barrier. The atomic_inc() works, but only if ->refcnt is set to zero on the initial allocation. That said, this approach seems safer, so: Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> > Signed-off-by: Patrick McHardy <kaber@trash.net> > > diff --git a/Documentation/RCU/rculist_nulls.txt b/Documentation/RCU/rculist_nulls.txt > index 6389dec..d0c017e 100644 > --- a/Documentation/RCU/rculist_nulls.txt > +++ b/Documentation/RCU/rculist_nulls.txt > @@ -83,11 +83,12 @@ not detect it missed following items in original chain. > obj = kmem_cache_alloc(...); > lock_chain(); // typically a spin_lock() > obj->key = key; > -atomic_inc(&obj->refcnt); > /* > * we need to make sure obj->key is updated before obj->next > + * or obj->refcnt > */ > smp_wmb(); > +atomic_set(&obj->refcnt, 1); > hlist_add_head_rcu(&obj->obj_node, list); > unlock_chain(); // typically a spin_unlock() > > @@ -159,6 +160,10 @@ out: > obj = kmem_cache_alloc(cachep); > lock_chain(); // typically a spin_lock() > obj->key = key; > +/* > + * changes to obj->key must be visible before refcnt one > + */ > +smp_wmb(); > atomic_set(&obj->refcnt, 1); > /* > * insert obj in RCU way (readers might be traversing chain) > diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c > index 2d3584f..0d961ee 100644 > --- a/net/netfilter/nf_conntrack_core.c > +++ b/net/netfilter/nf_conntrack_core.c > @@ -525,22 +525,37 @@ struct nf_conn *nf_conntrack_alloc(struct net *net, > } > } > > - ct = kmem_cache_zalloc(nf_conntrack_cachep, gfp); > + /* > + * Do not use kmem_cache_zalloc(), as this cache uses > + * SLAB_DESTROY_BY_RCU. > + */ > + ct = kmem_cache_alloc(nf_conntrack_cachep, gfp); > if (ct == NULL) { > pr_debug("nf_conntrack_alloc: Can't alloc conntrack.\n"); > atomic_dec(&net->ct.count); > return ERR_PTR(-ENOMEM); > } > - > - atomic_set(&ct->ct_general.use, 1); > + /* > + * Let ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode.next > + * and ct->tuplehash[IP_CT_DIR_REPLY].hnnode.next unchanged. > + */ > + memset(&ct->tuplehash[IP_CT_DIR_MAX], 0, > + sizeof(*ct) - offsetof(struct nf_conn, tuplehash[IP_CT_DIR_MAX])); > ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple = *orig; > + ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode.pprev = NULL; > ct->tuplehash[IP_CT_DIR_REPLY].tuple = *repl; > + ct->tuplehash[IP_CT_DIR_REPLY].hnnode.pprev = NULL; > /* Don't set timer yet: wait for confirmation */ > setup_timer(&ct->timeout, death_by_timeout, (unsigned long)ct); > #ifdef CONFIG_NET_NS > ct->ct_net = net; > #endif > > + /* > + * changes to lookup keys must be done before setting refcnt to 1 > + */ > + smp_wmb(); > + atomic_set(&ct->ct_general.use, 1); > return ct; > } > EXPORT_SYMBOL_GPL(nf_conntrack_alloc); > -- > To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- 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/Documentation/RCU/rculist_nulls.txt b/Documentation/RCU/rculist_nulls.txt index 6389dec..d0c017e 100644 --- a/Documentation/RCU/rculist_nulls.txt +++ b/Documentation/RCU/rculist_nulls.txt @@ -83,11 +83,12 @@ not detect it missed following items in original chain. obj = kmem_cache_alloc(...); lock_chain(); // typically a spin_lock() obj->key = key; -atomic_inc(&obj->refcnt); /* * we need to make sure obj->key is updated before obj->next + * or obj->refcnt */ smp_wmb(); +atomic_set(&obj->refcnt, 1); hlist_add_head_rcu(&obj->obj_node, list); unlock_chain(); // typically a spin_unlock() @@ -159,6 +160,10 @@ out: obj = kmem_cache_alloc(cachep); lock_chain(); // typically a spin_lock() obj->key = key; +/* + * changes to obj->key must be visible before refcnt one + */ +smp_wmb(); atomic_set(&obj->refcnt, 1); /* * insert obj in RCU way (readers might be traversing chain) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 2d3584f..0d961ee 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -525,22 +525,37 @@ struct nf_conn *nf_conntrack_alloc(struct net *net, } } - ct = kmem_cache_zalloc(nf_conntrack_cachep, gfp); + /* + * Do not use kmem_cache_zalloc(), as this cache uses + * SLAB_DESTROY_BY_RCU. + */ + ct = kmem_cache_alloc(nf_conntrack_cachep, gfp); if (ct == NULL) { pr_debug("nf_conntrack_alloc: Can't alloc conntrack.\n"); atomic_dec(&net->ct.count); return ERR_PTR(-ENOMEM); } - - atomic_set(&ct->ct_general.use, 1); + /* + * Let ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode.next + * and ct->tuplehash[IP_CT_DIR_REPLY].hnnode.next unchanged. + */ + memset(&ct->tuplehash[IP_CT_DIR_MAX], 0, + sizeof(*ct) - offsetof(struct nf_conn, tuplehash[IP_CT_DIR_MAX])); ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple = *orig; + ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode.pprev = NULL; ct->tuplehash[IP_CT_DIR_REPLY].tuple = *repl; + ct->tuplehash[IP_CT_DIR_REPLY].hnnode.pprev = NULL; /* Don't set timer yet: wait for confirmation */ setup_timer(&ct->timeout, death_by_timeout, (unsigned long)ct); #ifdef CONFIG_NET_NS ct->ct_net = net; #endif + /* + * changes to lookup keys must be done before setting refcnt to 1 + */ + smp_wmb(); + atomic_set(&ct->ct_general.use, 1); return ct; } EXPORT_SYMBOL_GPL(nf_conntrack_alloc);
commit 2b12e9634d9676c55f576195a7f950956179d881 Author: Patrick McHardy <kaber@trash.net> Date: Thu Jul 23 16:02:18 2009 +0200 netfilter: nf_conntrack: nf_conntrack_alloc() fixes Upstream commit 941297f4: When a slab cache uses SLAB_DESTROY_BY_RCU, we must be careful when allocating objects, since slab allocator could give a freed object still used by lockless readers. In particular, nf_conntrack RCU lookups rely on ct->tuplehash[xxx].hnnode.next being always valid (ie containing a valid 'nulls' value, or a valid pointer to next object in hash chain.) kmem_cache_zalloc() setups object with NULL values, but a NULL value is not valid for ct->tuplehash[xxx].hnnode.next. Fix is to call kmem_cache_alloc() and do the zeroing ourself. As spotted by Patrick, we also need to make sure lookup keys are committed to memory before setting refcount to 1, or a lockless reader could get a reference on the old version of the object. Its key re-check could then pass the barrier. Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Patrick McHardy <kaber@trash.net> -- 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