2.6.30-stable review patch. If anyone has any objections, please let us know. ------------------ From: Eric Dumazet commit 941297f443f871b8c3372feccf27a8733f6ce9e9 upstream. 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 Signed-off-by: Patrick McHardy Acked-by: Paul E. McKenney Signed-off-by: Greg Kroah-Hartman --- Documentation/RCU/rculist_nulls.txt | 7 ++++++- net/netfilter/nf_conntrack_core.c | 21 ++++++++++++++++++--- 2 files changed, 24 insertions(+), 4 deletions(-) --- a/Documentation/RCU/rculist_nulls.txt +++ b/Documentation/RCU/rculist_nulls.txt @@ -83,11 +83,12 @@ not detect it missed following items in 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) --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -525,22 +525,37 @@ struct nf_conn *nf_conntrack_alloc(struc } } - 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 netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html