[PATCH 5.16 18/28] netfilter: egress: silence egress hook lockdep splats

Greg Kroah-Hartman
2022-03-17T12:58:03Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit 17a8f31bba7bac8cce4bd12bab50697da96e7710 ]

Netfilter assumes its called with rcu_read_lock held, but in egress
hook case it may be called with BH readlock.

This triggers lockdep splat.

In order to avoid to change all rcu_dereference() to
rcu_dereference_check(..., rcu_read_lock_bh_held()), wrap nf_hook_slow
with read lock/unlock pair.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/netfilter_netdev.h | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/include/linux/netfilter_netdev.h b/include/linux/netfilter_netdev.h
index b4dd96e4dc8d..e6487a691136 100644
--- a/include/linux/netfilter_netdev.h
+++ b/include/linux/netfilter_netdev.h
@@ -101,7 +101,11 @@ static inline struct sk_buff *nf_hook_egress(struct sk_buff *skb, int *rc,
nf_hook_state_init(&state, NF_NETDEV_EGRESS,
NFPROTO_NETDEV, dev, NULL, NULL,
dev_net(dev), NULL);
+
+ /* nf assumes rcu_read_lock, not just read_lock_bh */
+ rcu_read_lock();
ret = nf_hook_slow(skb, &state, e, 0);
+ rcu_read_unlock();

if (ret == 1) {
return skb;
--
2.34.1