netdev - [PATCH net 1/2] net: avoid errors when trying to pop MLPS header on non-MPLS packets

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Message-Id: <9343e3ce8aed5d0e109ab0805fb452e8f55f0130.1570732834.git.dcaratti@redhat.com>
Date:   Thu, 10 Oct 2019 20:43:52 +0200
From:   Davide Caratti <dcaratti@...hat.com>
To:     "David S. Miller" <davem@...emloft.net>,
        John Hurley <john.hurley@...ronome.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH net 1/2] net: avoid errors when trying to pop MLPS header on non-MPLS packets

the following script:

 # tc qdisc add dev eth0 clsact
 # tc filter add dev eth0 egress matchall action mpls pop

implicitly makes the kernel drop all packets transmitted by eth0, if they
don't have a MPLS header. This behavior is uncommon: other encapsulations
(like VLAN) just let the packet pass unmodified. Since the result of MPLS
'pop' operation would be the same regardless of the presence / absence of
MPLS header(s) in the original packet, we can let skb_mpls_pop() return 0
when dealing with non-MPLS packets.

Fixes: 2a2ea50870ba ("net: sched: add mpls manipulation actions to TC")
Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---
 net/core/skbuff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 529133611ea2..cd59ccd6da57 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5536,7 +5536,7 @@ int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto)
 	int err;
 
 	if (unlikely(!eth_p_mpls(skb->protocol)))
-		return -EINVAL;
+		return 0;
 
 	err = skb_ensure_writable(skb, skb->mac_len + MPLS_HLEN);
 	if (unlikely(err))
-- 
2.21.0