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ipv4: Fix fib_trie rebalancing

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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 <zheng.yan@oracle.com>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jarek Poplawski 2009-06-15 02:31:29 -07:00 committed by David S. Miller
parent 3c4bdc4bd4
commit e0f7cb8c8c
1 changed files with 37 additions and 10 deletions
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47
net/ipv4/fib_trie.c
View file

@ -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;
}