netdev - [PATCH v4 net-next 2/8] hsr: Add a rcu-read lock to hsr_forward

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Date:   Fri, 25 Nov 2022 17:56:04 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH v4 net-next 2/8] hsr: Add a rcu-read lock to hsr_forward_skb().

hsr_forward_skb() a skb and keeps information in an on-stack
hsr_frame_info. hsr_get_node() assigns hsr_frame_info::node_src which is
from a RCU list. This pointer is used later in hsr_forward_do().
I don't see a reason why this pointer can't vanish midway since there is
no guarantee that hsr_forward_skb() is invoked from an RCU read section.

Use rcu_read_lock() to protect hsr_frame_info::node_src from its
assigment until it is no longer used.

Fixes: f266a683a4804 ("net/hsr: Better frame dispatch")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/hsr/hsr_forward.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
index 9894962847d97..3a97b00b6d978 100644
--- a/net/hsr/hsr_forward.c
+++ b/net/hsr/hsr_forward.c
@@ -613,11 +613,13 @@ void hsr_forward_skb(struct sk_buff *skb, struct hsr_port *port)
 {
 	struct hsr_frame_info frame;
 
+	rcu_read_lock();
 	if (fill_frame_info(&frame, skb, port) < 0)
 		goto out_drop;
 
 	hsr_register_frame_in(frame.node_src, port, frame.sequence_nr);
 	hsr_forward_do(&frame);
+	rcu_read_unlock();
 	/* Gets called for ingress frames as well as egress from master port.
 	 * So check and increment stats for master port only here.
 	 */
@@ -632,6 +634,7 @@ void hsr_forward_skb(struct sk_buff *skb, struct hsr_port *port)
 	return;
 
 out_drop:
+	rcu_read_unlock();
 	port->dev->stats.tx_dropped++;
 	kfree_skb(skb);
 }
-- 
2.38.1