From e0f7cb8c8cc6cccce28d2ce39ad8c60d23c3799f Mon Sep 17 00:00:00 2001 From: Jarek Poplawski Date: Mon, 15 Jun 2009 02:31:29 -0700 Subject: [PATCH] ipv4: Fix fib_trie rebalancing While doing trie_rebalance(): resize(), inflate(), halve() RCU free tnodes before updating their parents. It depends on RCU delaying the real destruction, but if RCU readers start after call_rcu() and before parent update they could access freed memory. It is currently prevented with preempt_disable() on the update side, but it's not safe, except maybe classic RCU, plus it conflicts with memory allocations with GFP_KERNEL flag used from these functions. This patch explicitly delays freeing of tnodes by adding them to the list, which is flushed after the update is finished. Reported-by: Yan Zheng Signed-off-by: Jarek Poplawski Signed-off-by: David S. Miller --- net/ipv4/fib_trie.c | 47 +++++++++++++++++++++++++++++++++++---------- 1 file changed, 37 insertions(+), 10 deletions(-) diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 538d2a9a5115..d1a39b1277d6 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -123,6 +123,7 @@ struct tnode { union { struct rcu_head rcu; struct work_struct work; + struct tnode *tnode_free; }; struct node *child[0]; }; @@ -161,6 +162,8 @@ static void tnode_put_child_reorg(struct tnode *tn, int i, struct node *n, static struct node *resize(struct trie *t, struct tnode *tn); static struct tnode *inflate(struct trie *t, struct tnode *tn); static struct tnode *halve(struct trie *t, struct tnode *tn); +/* tnodes to free after resize(); protected by RTNL */ +static struct tnode *tnode_free_head; static struct kmem_cache *fn_alias_kmem __read_mostly; static struct kmem_cache *trie_leaf_kmem __read_mostly; @@ -385,6 +388,29 @@ static inline void tnode_free(struct tnode *tn) call_rcu(&tn->rcu, __tnode_free_rcu); } +static void tnode_free_safe(struct tnode *tn) +{ + BUG_ON(IS_LEAF(tn)); + + if (node_parent((struct node *) tn)) { + tn->tnode_free = tnode_free_head; + tnode_free_head = tn; + } else { + tnode_free(tn); + } +} + +static void tnode_free_flush(void) +{ + struct tnode *tn; + + while ((tn = tnode_free_head)) { + tnode_free_head = tn->tnode_free; + tn->tnode_free = NULL; + tnode_free(tn); + } +} + static struct leaf *leaf_new(void) { struct leaf *l = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL); @@ -495,7 +521,7 @@ static struct node *resize(struct trie *t, struct tnode *tn) /* No children */ if (tn->empty_children == tnode_child_length(tn)) { - tnode_free(tn); + tnode_free_safe(tn); return NULL; } /* One child */ @@ -509,7 +535,7 @@ static struct node *resize(struct trie *t, struct tnode *tn) /* compress one level */ node_set_parent(n, NULL); - tnode_free(tn); + tnode_free_safe(tn); return n; } /* @@ -670,7 +696,7 @@ static struct node *resize(struct trie *t, struct tnode *tn) /* compress one level */ node_set_parent(n, NULL); - tnode_free(tn); + tnode_free_safe(tn); return n; } @@ -756,7 +782,7 @@ static struct tnode *inflate(struct trie *t, struct tnode *tn) put_child(t, tn, 2*i, inode->child[0]); put_child(t, tn, 2*i+1, inode->child[1]); - tnode_free(inode); + tnode_free_safe(inode); continue; } @@ -801,9 +827,9 @@ static struct tnode *inflate(struct trie *t, struct tnode *tn) put_child(t, tn, 2*i, resize(t, left)); put_child(t, tn, 2*i+1, resize(t, right)); - tnode_free(inode); + tnode_free_safe(inode); } - tnode_free(oldtnode); + tnode_free_safe(oldtnode); return tn; nomem: { @@ -885,7 +911,7 @@ static struct tnode *halve(struct trie *t, struct tnode *tn) put_child(t, newBinNode, 1, right); put_child(t, tn, i/2, resize(t, newBinNode)); } - tnode_free(oldtnode); + tnode_free_safe(oldtnode); return tn; nomem: { @@ -989,7 +1015,6 @@ static struct node *trie_rebalance(struct trie *t, struct tnode *tn) t_key cindex, key; struct tnode *tp; - preempt_disable(); key = tn->key; while (tn != NULL && (tp = node_parent((struct node *)tn)) != NULL) { @@ -1001,16 +1026,18 @@ static struct node *trie_rebalance(struct trie *t, struct tnode *tn) (struct node *)tn, wasfull); tp = node_parent((struct node *) tn); + tnode_free_flush(); if (!tp) break; tn = tp; } /* Handle last (top) tnode */ - if (IS_TNODE(tn)) + if (IS_TNODE(tn)) { tn = (struct tnode *)resize(t, (struct tnode *)tn); + tnode_free_flush(); + } - preempt_enable(); return (struct node *)tn; } -- 2.34.1