netdev - [PATCH iproute2] iproute2: fix MPLS label parsing

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Date:   Wed, 11 Mar 2020 16:16:36 +0100
From:   Guillaume Nault <gnault@...hat.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org
Subject: [PATCH iproute2] iproute2: fix MPLS label parsing

The initial value of "label" in parse_mpls() is 0xffffffff. Therefore
we should test for this value, and not 0, to detect if a label has been
provided. The "!label" test not only fails to detect a missing label
parameter, it also prevents the use of the IPv4 explicit NULL label,
which actually equals 0.

Reproducer:
  $ ip link add name dm0 type dummy
  $ tc qdisc add dev dm0 ingress

  $ tc filter add dev dm0 parent ffff: matchall action mpls push
  Error: act_mpls: Label is required for MPLS push.
  We have an error talking to the kernel
  --> Filter was pushed to the kernel, where it got rejected.

  $ tc filter add dev dm0 parent ffff: matchall action mpls push label 0
  Error: argument "label" is required
  --> Label 0 was rejected by iproute2.

Expected result:
  $ tc filter add dev dm0 parent ffff: matchall action mpls push
  Error: argument "label" is required
  --> Filter was directly rejected by iproute2.

  $ tc filter add dev dm0 parent ffff: matchall action mpls push label 0
  --> Filter is accepted.

Signed-off-by: Guillaume Nault <gnault@...hat.com>
---
 tc/m_mpls.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tc/m_mpls.c b/tc/m_mpls.c
index 6f3a39f4..50eba01c 100644
--- a/tc/m_mpls.c
+++ b/tc/m_mpls.c
@@ -156,7 +156,7 @@ static int parse_mpls(struct action_util *a, int *argc_p, char ***argv_p,
 		}
 	}
 
-	if (action == TCA_MPLS_ACT_PUSH && !label)
+	if (action == TCA_MPLS_ACT_PUSH && label == 0xffffffff)
 		missarg("label");
 
 	if (action == TCA_MPLS_ACT_PUSH && proto &&
-- 
2.21.1