linux-kernel - [PATCH AUTOSEL 5.16 18/27] netfilter: egress: silence egress hook lockdep splats

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Message-Id: <20220309161711.135679-18-sashal@kernel.org>
Date:   Wed,  9 Mar 2022 11:16:55 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Florian Westphal <fw@...len.de>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Sasha Levin <sashal@...nel.org>, kadlec@...filter.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org
Subject: [PATCH AUTOSEL 5.16 18/27] netfilter: egress: silence egress hook lockdep splats

From: Florian Westphal <fw@...len.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@...il.com>
Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Sasha Levin <sashal@...nel.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