[PATCH v3 bpf 1/2] bpf: fix skb_do_redirect return values

[Yan Zhai <yan@cloudflare.com>]

skb_do_redirect returns various of values: error code (negative), 0
(success), and some positive status code, e.g. NET_XMIT_CN, NET_RX_DROP.
Such code are not handled at lwt xmit hook in function ip_finish_output2
and ip6_finish_output, which can cause unexpected problems. This change
converts the positive status code to proper error code.

Suggested-by: Stanislav Fomichev <sdf@google.com>
Reported-by: Jordan Griege <jgriege@cloudflare.com>
Signed-off-by: Yan Zhai <yan@cloudflare.com>

---
v3: converts also RX side return value in addition to TX values
v2: code style change suggested by Stanislav Fomichev
---
 net/core/filter.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 06ba0e56e369..3e232ce11ca0 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2095,7 +2095,12 @@ static const struct bpf_func_proto bpf_csum_level_proto = {
 
 static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
 {
-	return dev_forward_skb_nomtu(dev, skb);
+	int ret = dev_forward_skb_nomtu(dev, skb);
+
+	if (unlikely(ret > 0))
+		return -ENETDOWN;
+
+	return 0;
 }
 
 static inline int __bpf_rx_skb_no_mac(struct net_device *dev,
@@ -2106,6 +2111,8 @@ static inline int __bpf_rx_skb_no_mac(struct net_device *dev,
 	if (likely(!ret)) {
 		skb->dev = dev;
 		ret = netif_rx(skb);
+	} else if (ret > 0) {
+		return -ENETDOWN;
 	}
 
 	return ret;
@@ -2129,6 +2136,9 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)
 	ret = dev_queue_xmit(skb);
 	dev_xmit_recursion_dec();
 
+	if (unlikely(ret > 0))
+		ret = net_xmit_errno(ret);
+
 	return ret;
 }
 
-- 
2.30.2