[PATCH v6.1.y 1/4] net: dst: add four helpers to annotate data-races around dst->dev

[Miguel Gazquez (Schneider Electric)]

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit 88fe14253e181878c2ddb51a298ae8c468a63010 ]

dst->dev is read locklessly in many contexts,
and written in dst_dev_put().

Fixing all the races is going to need many changes.

We probably will have to add full RCU protection.

Add three helpers to ease this painful process.

static inline struct net_device *dst_dev(const struct dst_entry *dst)
{
       return READ_ONCE(dst->dev);
}

static inline struct net_device *skb_dst_dev(const struct sk_buff *skb)
{
       return dst_dev(skb_dst(skb));
}

static inline struct net *skb_dst_dev_net(const struct sk_buff *skb)
{
       return dev_net(skb_dst_dev(skb));
}

static inline struct net *skb_dst_dev_net_rcu(const struct sk_buff *skb)
{
       return dev_net_rcu(skb_dst_dev(skb));
}

Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Link: https://patch.msgid.link/20250630121934.3399505-7-edumazet@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
[ minor modifications to fix conflict ]
Signed-off-by: Miguel Gazquez <miguel.gazquez@xxxxxxxxxxx>
---
 include/net/dst.h | 20 ++++++++++++++++++++
 net/core/dst.c    |  4 ++--
 net/core/sock.c   |  6 +++---
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/net/dst.h b/include/net/dst.h
index 20a76e532afb..7c0cf856154d 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -555,6 +555,11 @@ static inline void skb_dst_update_pmtu_no_confirm(struct sk_buff *skb, u32 mtu)
 		dst->ops->update_pmtu(dst, NULL, skb, mtu, false);
 }
 
+static inline struct net_device *dst_dev(const struct dst_entry *dst)
+{
+	return READ_ONCE(dst->dev);
+}
+
 static inline struct net_device *dst_dev_rcu(const struct dst_entry *dst)
 {
 	/* In the future, use rcu_dereference(dst->dev) */
@@ -562,11 +567,26 @@ static inline struct net_device *dst_dev_rcu(const struct dst_entry *dst)
 	return READ_ONCE(dst->dev);
 }
 
+static inline struct net_device *skb_dst_dev(const struct sk_buff *skb)
+{
+	return dst_dev(skb_dst(skb));
+}
+
 static inline struct net_device *skb_dst_dev_rcu(const struct sk_buff *skb)
 {
 	return dst_dev_rcu(skb_dst(skb));
 }
 
+static inline struct net *skb_dst_dev_net(const struct sk_buff *skb)
+{
+	return dev_net(skb_dst_dev(skb));
+}
+
+static inline struct net *skb_dst_dev_net_rcu(const struct sk_buff *skb)
+{
+	return dev_net_rcu(skb_dst_dev(skb));
+}
+
 struct dst_entry *dst_blackhole_check(struct dst_entry *dst, u32 cookie);
 void dst_blackhole_update_pmtu(struct dst_entry *dst, struct sock *sk,
 			       struct sk_buff *skb, u32 mtu, bool confirm_neigh);
diff --git a/net/core/dst.c b/net/core/dst.c
index 8db87258d145..24a1cc3d2a08 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -151,7 +151,7 @@ void dst_dev_put(struct dst_entry *dst)
 		dst->ops->ifdown(dst, dev, true);
 	dst->input = dst_discard;
 	dst->output = dst_discard_out;
-	dst->dev = blackhole_netdev;
+	WRITE_ONCE(dst->dev, blackhole_netdev);
 	netdev_ref_replace(dev, blackhole_netdev, &dst->dev_tracker,
 			   GFP_ATOMIC);
 }
@@ -272,7 +272,7 @@ unsigned int dst_blackhole_mtu(const struct dst_entry *dst)
 {
 	unsigned int mtu = dst_metric_raw(dst, RTAX_MTU);
 
-	return mtu ? : dst->dev->mtu;
+	return mtu ? : dst_dev(dst)->mtu;
 }
 EXPORT_SYMBOL_GPL(dst_blackhole_mtu);
 
diff --git a/net/core/sock.c b/net/core/sock.c
index 2a701e0b052b..64f9d77bfaec 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2397,7 +2397,7 @@ void sk_setup_caps(struct sock *sk, struct dst_entry *dst)
 {
 	u32 max_segs = 1;
 
-	sk->sk_route_caps = dst->dev->features;
+	sk->sk_route_caps = dst_dev(dst)->features;
 	if (sk_is_tcp(sk))
 		sk->sk_route_caps |= NETIF_F_GSO;
 	if (sk->sk_route_caps & NETIF_F_GSO)
@@ -2410,11 +2410,11 @@ void sk_setup_caps(struct sock *sk, struct dst_entry *dst)
 		} else {
 			sk->sk_route_caps |= NETIF_F_SG | NETIF_F_HW_CSUM;
 			/* pairs with the WRITE_ONCE() in netif_set_gso_max_size() */
-			sk->sk_gso_max_size = READ_ONCE(dst->dev->gso_max_size);
+			sk->sk_gso_max_size = READ_ONCE(dst_dev(dst)->gso_max_size);
 			sk_trim_gso_size(sk);
 			sk->sk_gso_max_size -= (MAX_TCP_HEADER + 1);
 			/* pairs with the WRITE_ONCE() in netif_set_gso_max_segs() */
-			max_segs = max_t(u32, READ_ONCE(dst->dev->gso_max_segs), 1);
+			max_segs = max_t(u32, READ_ONCE(dst_dev(dst)->gso_max_segs), 1);
 		}
 	}
 	sk->sk_gso_max_segs = max_segs;

-- 
2.55.0