Subject: [PATCH v2 1/1] net: gro: fix misuse of CB in udp socket lookup

From: Richard Gobert <[email-masked]>
Date: Thu, 20 Jul 2023 18:26:27 +0200

This patch fixes a misuse of IP{6}CB(skb) in GRO, while calling to
`udp6_lib_lookup2` when handling udp tunnels. `udp6_lib_lookup2` fetch the
device from CB. The fix changes it to fetch the device from `skb->dev`.
l3mdev case requires special attention since it has a master and a slave
device.

Fixes: a6024562ffd7 ("udp: Add GRO functions to UDP socket")
Reported-by: Gal Pressman <[email-masked]>
Signed-off-by: Richard Gobert <[email-masked]>
---
 include/net/udp.h      |  2 ++
 net/ipv4/udp.c         | 28 ++++++++++++++++++++++++++--
 net/ipv4/udp_offload.c |  7 +++++--
 net/ipv6/udp.c         | 29 +++++++++++++++++++++++++++--
 net/ipv6/udp_offload.c |  7 +++++--
 5 files changed, 65 insertions(+), 8 deletions(-)

diff --git a/include/net/udp.h b/include/net/udp.h
index 4d13424f8f72..48af1479882f 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -299,6 +299,7 @@ int udp_lib_getsockopt(struct sock *sk, int level, int optname,
 int udp_lib_setsockopt(struct sock *sk, int level, int optname,
 		       sockptr_t optval, unsigned int optlen,
 		       int (*push_pending_frames)(struct sock *));
+void udp4_get_iif_sdif(const struct sk_buff *skb, int *iif, int *sdif);
 struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
 			     __be32 daddr, __be16 dport, int dif);
 struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
@@ -310,6 +311,7 @@ struct sock *udp6_lib_lookup(struct net *net,
 			     const struct in6_addr *saddr, __be16 sport,
 			     const struct in6_addr *daddr, __be16 dport,
 			     int dif);
+void udp6_get_iif_sdif(const struct sk_buff *skb, int *iif, int *sdif);
 struct sock *__udp6_lib_lookup(struct net *net,
 			       const struct in6_addr *saddr, __be16 sport,
 			       const struct in6_addr *daddr, __be16 dport,
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 8c3ebd95f5b9..85eb9977db2c 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -550,15 +550,39 @@ static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
 				 inet_sdif(skb), udptable, skb);
 }
 
+/* This function is the alternative to 'inet_iif' and 'inet_sdif'
+ * functions in case we can not rely on fields of IPCB.
+ *
+ * The caller must verify skb_valid_dst(skb) is false and skb->dev is initialized.
+ * The caller must hold the RCU read lock.
+ */
+inline void udp4_get_iif_sdif(const struct sk_buff *skb, int *iif, int *sdif)
+{
+	*iif = inet_iif(skb) ?: skb->dev->ifindex;
+	*sdif = 0;
+
+#if IS_ENABLED(CONFIG_NET_L3_MASTER_DEV)
+	if (netif_is_l3_slave(skb->dev)) {
+		struct net_device *master = netdev_master_upper_dev_get_rcu(skb->dev);
+
+		*sdif = *iif;
+		*iif = master ? master->ifindex : 0;
+	}
+#endif
+}
+
 struct sock *udp4_lib_lookup_skb(const struct sk_buff *skb,
 				 __be16 sport, __be16 dport)
 {
 	const struct iphdr *iph = ip_hdr(skb);
 	struct net *net = dev_net(skb->dev);
+	int iif, sdif;
+
+	udp4_get_iif_sdif(skb, &iif, &sdif);
 
 	return __udp4_lib_lookup(net, iph->saddr, sport,
-				 iph->daddr, dport, inet_iif(skb),
-				 inet_sdif(skb), net->ipv4.udp_table, NULL);
+				 iph->daddr, dport, iif,
+				 sdif, net->ipv4.udp_table, NULL);
 }
 
 /* Must be called under rcu_read_lock().
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 75aa4de5b731..70d760b271db 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -603,10 +603,13 @@ static struct sock *udp4_gro_lookup_skb(struct sk_buff *skb, __be16 sport,
 {
 	const struct iphdr *iph = skb_gro_network_header(skb);
 	struct net *net = dev_net(skb->dev);
+	int iif, sdif;
+
+	udp4_get_iif_sdif(skb, &iif, &sdif);
 
 	return __udp4_lib_lookup(net, iph->saddr, sport,
-				 iph->daddr, dport, inet_iif(skb),
-				 inet_sdif(skb), net->ipv4.udp_table, NULL);
+				 iph->daddr, dport, iif,
+				 sdif, net->ipv4.udp_table, NULL);
 }
 
 INDIRECT_CALLABLE_SCOPE
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index b7c972aa09a7..6dbcadc3bf8f 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -295,15 +295,40 @@ static struct sock *__udp6_lib_lookup_skb(struct sk_buff *skb,
 				 inet6_sdif(skb), udptable, skb);
 }
 
+/* This function is the alternative to 'inet6_iif' and 'inet6_sdif'
+ * functions in case we can not rely on fields of IP6CB.
+ *
+ * The caller must verify skb_valid_dst(skb) is false and skb->dev is initialized.
+ * The caller must hold the RCU read lock.
+ */
+inline void udp6_get_iif_sdif(const struct sk_buff *skb, int *iif, int *sdif)
+{
+	/* using skb->dev->ifindex because skb_dst(skb) is not initialized */
+	*iif = skb->dev->ifindex;
+	*sdif = 0;
+
+#if IS_ENABLED(CONFIG_NET_L3_MASTER_DEV)
+	if (netif_is_l3_slave(skb->dev)) {
+		struct net_device *master = netdev_master_upper_dev_get_rcu(skb->dev);
+
+		*sdif = *iif;
+		*iif = master ? master->ifindex : 0;
+	}
+#endif
+}
+
 struct sock *udp6_lib_lookup_skb(const struct sk_buff *skb,
 				 __be16 sport, __be16 dport)
 {
 	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	struct net *net = dev_net(skb->dev);
+	int iif, sdif;
+
+	udp6_get_iif_sdif(skb, &iif, &sdif);
 
 	return __udp6_lib_lookup(net, &iph->saddr, sport,
-				 &iph->daddr, dport, inet6_iif(skb),
-				 inet6_sdif(skb), net->ipv4.udp_table, NULL);
+				 &iph->daddr, dport, iif,
+				 sdif, net->ipv4.udp_table, NULL);
 }
 
 /* Must be called under rcu_read_lock().
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index ad3b8726873e..88191d79002e 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -119,10 +119,13 @@ static struct sock *udp6_gro_lookup_skb(struct sk_buff *skb, __be16 sport,
 {
 	const struct ipv6hdr *iph = skb_gro_network_header(skb);
 	struct net *net = dev_net(skb->dev);
+	int iif, sdif;
+
+	udp6_get_iif_sdif(skb, &iif, &sdif);
 
 	return __udp6_lib_lookup(net, &iph->saddr, sport,
-				 &iph->daddr, dport, inet6_iif(skb),
-				 inet6_sdif(skb), net->ipv4.udp_table, NULL);
+				 &iph->daddr, dport, iif,
+				 sdif, net->ipv4.udp_table, NULL);
 }
 
 INDIRECT_CALLABLE_SCOPE
-- 
2.36.1