net: ip: make ip_route_use_hint() return drop reasons

JIRA: https://issues.redhat.com/browse/RHEL-88891
Upstream Status: linux.git
Conflicts:\
- Minor code differences as the tos to dscp conversion wasn't done in
  c10s yet.

commit 479aed0
Author: Menglong Dong <menglong8.dong@gmail.com>
Date:   Thu Nov 7 20:56:01 2024 +0800

    net: ip: make ip_route_use_hint() return drop reasons

    In this commit, we make ip_route_use_hint() return drop reasons. The
    drop reasons that we return are similar to what we do in
    ip_route_input_slow(), and no drop reasons are added in this commit.

    Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Signed-off-by: Antoine Tenart <atenart@redhat.com>

Author: atenart

include/net/route.h

@@ -206,9 +206,10 @@ ip_mc_validate_source(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 enum skb_drop_reason
 ip_route_input_noref(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 		     u8 tos, struct net_device *dev);
-int ip_route_use_hint(struct sk_buff *skb, __be32 dst, __be32 src,
-		      u8 tos, struct net_device *devin,
-		      const struct sk_buff *hint);
+enum skb_drop_reason
+ip_route_use_hint(struct sk_buff *skb, __be32 daddr, __be32 saddr,
+		  u8 tos, struct net_device *dev,
+		  const struct sk_buff *hint);
 
 static inline enum skb_drop_reason
 ip_route_input(struct sk_buff *skb, __be32 dst, __be32 src, u8 tos,

net/ipv4/ip_input.c

@@ -322,15 +322,14 @@ static int ip_rcv_finish_core(struct net *net, struct sock *sk,
 	int err, drop_reason;
 	struct rtable *rt;
 
-	drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
-
 	if (ip_can_use_hint(skb, iph, hint)) {
-		err = ip_route_use_hint(skb, iph->daddr, iph->saddr, iph->tos,
-					dev, hint);
-		if (unlikely(err))
+		drop_reason = ip_route_use_hint(skb, iph->daddr, iph->saddr,
+						iph->tos, dev, hint);
+		if (unlikely(drop_reason))
 			goto drop_error;
 	}
 
+	drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	if (READ_ONCE(net->ipv4.sysctl_ip_early_demux) &&
 	    !skb_dst(skb) &&
 	    !skb->sk &&

net/ipv4/route.c

@@ -2152,28 +2152,34 @@ ip_mkroute_input(struct sk_buff *skb, struct fib_result *res,
  * assuming daddr is valid and the destination is not a local broadcast one.
  * Uses the provided hint instead of performing a route lookup.
  */
-int ip_route_use_hint(struct sk_buff *skb, __be32 daddr, __be32 saddr,
-		      u8 tos, struct net_device *dev,
-		      const struct sk_buff *hint)
+enum skb_drop_reason
+ip_route_use_hint(struct sk_buff *skb, __be32 daddr, __be32 saddr,
+		  u8 tos, struct net_device *dev,
+		  const struct sk_buff *hint)
 {
+	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	struct in_device *in_dev = __in_dev_get_rcu(dev);
 	struct rtable *rt = skb_rtable(hint);
 	struct net *net = dev_net(dev);
-	enum skb_drop_reason reason;
-	int err = -EINVAL;
 	u32 tag = 0;
 
 	if (!in_dev)
-		return -EINVAL;
+		return reason;
 
-	if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr))
+	if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr)) {
+		reason = SKB_DROP_REASON_IP_INVALID_SOURCE;
 		goto martian_source;
+	}
 
-	if (ipv4_is_zeronet(saddr))
+	if (ipv4_is_zeronet(saddr)) {
+		reason = SKB_DROP_REASON_IP_INVALID_SOURCE;
 		goto martian_source;
+	}
 
-	if (ipv4_is_loopback(saddr) && !IN_DEV_NET_ROUTE_LOCALNET(in_dev, net))
+	if (ipv4_is_loopback(saddr) && !IN_DEV_NET_ROUTE_LOCALNET(in_dev, net)) {
+		reason = SKB_DROP_REASON_IP_LOCALNET;
 		goto martian_source;
+	}
 
 	if (rt->rt_type != RTN_LOCAL)
 		goto skip_validate_source;
@@ -2186,11 +2192,11 @@ int ip_route_use_hint(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 
 skip_validate_source:
 	skb_dst_copy(skb, hint);
-	return 0;
+	return SKB_NOT_DROPPED_YET;
 
 martian_source:
 	ip_handle_martian_source(dev, in_dev, skb, daddr, saddr);
-	return err;
+	return reason;
 }
 
 /* get device for dst_alloc with local routes */