[PATCH net-next 4/7] net: ip: make fib_validate_source() return drop reason

[Menglong Dong]

In this commit, we make fib_validate_source/__fib_validate_source return
-reason instead of errno on error. As the return value of them can be
-errno, 0, and 1, we can't make it return enum skb_drop_reason directly.

In the origin logic, if __fib_validate_source() return -EXDEV,
LINUX_MIB_IPRPFILTER will be counted. And now, we need to adjust it by
checking "reason == SKB_DROP_REASON_IP_RPFILTER".

We set the errno to -EINVAL when fib_validate_source() is called and the
validation fails, as the errno can be checked in the caller and now its
value is -reason, which can lead misunderstand.

Signed-off-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
---
 net/ipv4/fib_frontend.c | 19 +++++++++++++------
 net/ipv4/ip_input.c     |  4 +---
 net/ipv4/route.c        | 17 +++++++++++++----
 3 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 793e6781399a..779c90de3a54 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -346,6 +346,7 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 				 int rpf, struct in_device *idev, u32 *itag)
 {
 	struct net *net = dev_net(dev);
+	enum skb_drop_reason reason;
 	struct flow_keys flkeys;
 	int ret, no_addr;
 	struct fib_result res;
@@ -377,9 +378,15 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 
 	if (fib_lookup(net, &fl4, &res, 0))
 		goto last_resort;
-	if (res.type != RTN_UNICAST &&
-	    (res.type != RTN_LOCAL || !IN_DEV_ACCEPT_LOCAL(idev)))
-		goto e_inval;
+	if (res.type != RTN_UNICAST) {
+		if (res.type != RTN_LOCAL) {
+			reason = SKB_DROP_REASON_IP_INVALID_SOURCE;
+			goto e_inval;
+		} else if (!IN_DEV_ACCEPT_LOCAL(idev)) {
+			reason = SKB_DROP_REASON_IP_LOCAL_SOURCE;
+			goto e_inval;
+		}
+	}
 	fib_combine_itag(itag, &res);
 
 	dev_match = fib_info_nh_uses_dev(res.fi, dev);
@@ -412,9 +419,9 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 	return 0;
 
 e_inval:
-	return -EINVAL;
+	return -reason;
 e_rpf:
-	return -EXDEV;
+	return -SKB_DROP_REASON_IP_RPFILTER;
 }
 
 /* Ignore rp_filter for packets protected by IPsec. */
@@ -440,7 +447,7 @@ int fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 		 * and the same host but different containers are not.
 		 */
 		if (inet_lookup_ifaddr_rcu(net, src))
-			return -EINVAL;
+			return -SKB_DROP_REASON_IP_LOCAL_SOURCE;
 
 ok:
 		*itag = 0;
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index dc062ae49137..aac0575bb1a4 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -424,10 +424,8 @@ static int ip_rcv_finish_core(struct net *net, struct sock *sk,
 	return NET_RX_DROP;
 
 drop_error:
-	if (err == -EXDEV) {
-		drop_reason = SKB_DROP_REASON_IP_RPFILTER;
+	if (drop_reason == SKB_DROP_REASON_IP_RPFILTER)
 		__NET_INC_STATS(net, LINUX_MIB_IPRPFILTER);
-	}
 	goto drop;
 }
 
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index ab70917c62e5..9de85051463b 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1690,7 +1690,7 @@ int ip_mc_validate_source(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 		err = fib_validate_source(skb, saddr, 0, tos, 0, dev,
 					  in_dev, itag);
 		if (err < 0)
-			return err;
+			return -EINVAL;
 	}
 	return 0;
 }
@@ -1788,6 +1788,7 @@ static int __mkroute_input(struct sk_buff *skb,
 	err = fib_validate_source(skb, saddr, daddr, tos, FIB_RES_OIF(*res),
 				  in_dev->dev, in_dev, &itag);
 	if (err < 0) {
+		err = -EINVAL;
 		ip_handle_martian_source(in_dev->dev, in_dev, skb, daddr,
 					 saddr);
 
@@ -2162,8 +2163,10 @@ int ip_route_use_hint(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 
 	tos &= INET_DSCP_MASK;
 	err = fib_validate_source(skb, saddr, daddr, tos, 0, dev, in_dev, &tag);
-	if (err < 0)
+	if (err < 0) {
+		err = -EINVAL;
 		goto martian_source;
+	}
 
 skip_validate_source:
 	skb_dst_copy(skb, hint);
@@ -2313,8 +2316,11 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 	if (res->type == RTN_LOCAL) {
 		err = fib_validate_source(skb, saddr, daddr, tos,
 					  0, dev, in_dev, &itag);
-		if (err < 0)
+		if (err < 0) {
+			__reason = -err;
+			err = -EINVAL;
 			goto martian_source;
+		}
 		goto local_input;
 	}
 
@@ -2339,8 +2345,11 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 	if (!ipv4_is_zeronet(saddr)) {
 		err = fib_validate_source(skb, saddr, 0, tos, 0, dev,
 					  in_dev, &itag);
-		if (err < 0)
+		if (err < 0) {
+			__reason = -err;
+			err = -EINVAL;
 			goto martian_source;
+		}
 	}
 	flags |= RTCF_BROADCAST;
 	res->type = RTN_BROADCAST;
-- 
2.39.5