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netfilter: nf_conncount: split gc in two phases 

The lockless workqueue garbage collector can race with packet path
garbage collector to delete list nodes, as it calls tree_nodes_free()
with the addresses of nodes that might have been free'd already from
another cpu.

To fix this, split gc into two phases.

One phase to perform gc on the connections: From a locking perspective,
this is the same as count_tree(): we hold rcu lock, but we do not
change the tree, we only change the nodes' contents.

The second phase acquires the tree lock and reaps empty nodes.
This avoids a race condition of the garbage collection vs.  packet path:
If a node has been free'd already, the second phase won't find it anymore.

This second phase is, from locking perspective, same as insert_tree().

The former only modifies nodes (list content, count), latter modifies
the tree itself (rb_erase or rb_insert).

Fixes: 5c789e131c ("netfilter: nf_conncount: Add list lock and gc worker, and RCU for init tree search")
Reviewed-by: Shawn Bohrer <sbohrer@cloudflare.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2018-12-28 01:24:44 +01:00 committed by Pablo Neira Ayuso
parent 4cd273bb91
commit f7fcc98dfc
1 changed files with 19 additions and 3 deletions
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20
net/netfilter/nf_conncount.c
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@ -500,16 +500,32 @@ static void tree_gc_worker(struct work_struct *work)
for (node = rb_first(root); node != NULL; node = rb_next(node)) {
rbconn = rb_entry(node, struct nf_conncount_rb, node);
if (nf_conncount_gc_list(data->net, &rbconn->list))
gc_nodes[gc_count++] = rbconn;
gc_count++;
}
rcu_read_unlock();
spin_lock_bh(&nf_conncount_locks[tree]);
if (gc_count < ARRAY_SIZE(gc_nodes))
goto next; /* do not bother */
if (gc_count) {
gc_count = 0;
node = rb_first(root);
while (node != NULL) {
rbconn = rb_entry(node, struct nf_conncount_rb, node);
node = rb_next(node);
if (rbconn->list.count > 0)
continue;
gc_nodes[gc_count++] = rbconn;
if (gc_count >= ARRAY_SIZE(gc_nodes)) {
tree_nodes_free(root, gc_nodes, gc_count);
gc_count = 0;
}
}
tree_nodes_free(root, gc_nodes, gc_count);
next:
clear_bit(tree, data->pending_trees);
next_tree = (tree + 1) % CONNCOUNT_SLOTS;