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Subject[PATCH 4.20 008/111] netfilter: nf_conncount: split gc in two phases
Date
4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <fw@strlen.de>

commit f7fcc98dfc2d136722007fec0debbed761679b94 upstream.

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: 5c789e131cbb9 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/netfilter/nf_conncount.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)

--- a/net/netfilter/nf_conncount.c
+++ b/net/netfilter/nf_conncount.c
@@ -500,16 +500,32 @@ static void tree_gc_worker(struct work_s
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) {
- tree_nodes_free(root, gc_nodes, 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;

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