From: Eric Dumazet <edumazet@google.com>
Date: Mon, 30 Jun 2025 12:19:29 +0000 (+0000)
Subject: net: dst: annotate data-races around dst->output
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=2dce8c52a98995c4719def6f88629ab1581c0b82;p=thirdparty%2Flinux.git

net: dst: annotate data-races around dst->output

dst_dev_put() can overwrite dst->output while other
cpus might read this field (for instance from dst_output())

Add READ_ONCE()/WRITE_ONCE() annotations to suppress
potential issues.

We will likely need RCU protection in the future.

Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250630121934.3399505-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---

diff --git a/include/net/dst.h b/include/net/dst.h
index c0f8b6d8e7074..b6acfde7d587c 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -458,7 +458,7 @@ INDIRECT_CALLABLE_DECLARE(int ip_output(struct net *, struct sock *,
 /* Output packet to network from transport.  */
 static inline int dst_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
-	return INDIRECT_CALL_INET(skb_dst(skb)->output,
+	return INDIRECT_CALL_INET(READ_ONCE(skb_dst(skb)->output),
 				  ip6_output, ip_output,
 				  net, sk, skb);
 }
diff --git a/include/net/lwtunnel.h b/include/net/lwtunnel.h
index eaac07d505959..26232f603e33c 100644
--- a/include/net/lwtunnel.h
+++ b/include/net/lwtunnel.h
@@ -138,8 +138,8 @@ int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len,
 static inline void lwtunnel_set_redirect(struct dst_entry *dst)
 {
 	if (lwtunnel_output_redirect(dst->lwtstate)) {
-		dst->lwtstate->orig_output = dst->output;
-		dst->output = lwtunnel_output;
+		dst->lwtstate->orig_output = READ_ONCE(dst->output);
+		WRITE_ONCE(dst->output, lwtunnel_output);
 	}
 	if (lwtunnel_input_redirect(dst->lwtstate)) {
 		dst->lwtstate->orig_input = READ_ONCE(dst->input);
diff --git a/net/core/dst.c b/net/core/dst.c
index 13c629dc7123d..52e824e57c175 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -149,7 +149,7 @@ void dst_dev_put(struct dst_entry *dst)
 	if (dst->ops->ifdown)
 		dst->ops->ifdown(dst, dev);
 	WRITE_ONCE(dst->input, dst_discard);
-	dst->output = dst_discard_out;
+	WRITE_ONCE(dst->output, dst_discard_out);
 	dst->dev = blackhole_netdev;
 	netdev_ref_replace(dev, blackhole_netdev, &dst->dev_tracker,
 			   GFP_ATOMIC);
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 75a1f9eabd6b6..ce6aba4f01ff2 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1688,7 +1688,7 @@ struct rtable *rt_dst_clone(struct net_device *dev, struct rtable *rt)
 			new_rt->rt_gw6 = rt->rt_gw6;
 
 		new_rt->dst.input = READ_ONCE(rt->dst.input);
-		new_rt->dst.output = rt->dst.output;
+		new_rt->dst.output = READ_ONCE(rt->dst.output);
 		new_rt->dst.error = rt->dst.error;
 		new_rt->dst.lastuse = jiffies;
 		new_rt->dst.lwtstate = lwtstate_get(rt->dst.lwtstate);