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From:   Balazs Nemeth <bnemeth@redhat.com>
To:     netdev@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, mst@redhat.com, jasowang@redhat.com,
        dsahern@gmail.com, davem@davemloft.net, willemb@google.com,
        virtualization@lists.linux-foundation.org, bnemeth@redhat.com
Subject: [PATCH net v3 2/2] net: avoid infinite loop in mpls_gso_segment when mpls_hlen == 0
Date:   Tue,  9 Mar 2021 12:31:01 +0100
Message-Id: <9b79f43d2dfec8b2cb8e896b5591e7b1c3cc1f6c.1615288658.git.bnemeth@redhat.com>
In-Reply-To: <cover.1615288658.git.bnemeth@redhat.com>
References: <cover.1615288658.git.bnemeth@redhat.com>
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A packet with skb_inner_network_header(skb) == skb_network_header(skb)
and ETH_P_MPLS_UC will prevent mpls_gso_segment from pulling any headers
from the packet. Subsequently, the call to skb_mac_gso_segment will
again call mpls_gso_segment with the same packet leading to an infinite
loop. In addition, ensure that the header length is a multiple of four,
which should hold irrespective of the number of stacked labels.

Signed-off-by: Balazs Nemeth <bnemeth@redhat.com>
---
 net/mpls/mpls_gso.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mpls/mpls_gso.c b/net/mpls/mpls_gso.c
index b1690149b6fa..1482259de9b5 100644
--- a/net/mpls/mpls_gso.c
+++ b/net/mpls/mpls_gso.c
@@ -14,6 +14,7 @@
 #include <linux/netdev_features.h>
 #include <linux/netdevice.h>
 #include <linux/skbuff.h>
+#include <net/mpls.h>
 
 static struct sk_buff *mpls_gso_segment(struct sk_buff *skb,
 				       netdev_features_t features)
@@ -27,6 +28,8 @@ static struct sk_buff *mpls_gso_segment(struct sk_buff *skb,
 
 	skb_reset_network_header(skb);
 	mpls_hlen = skb_inner_network_header(skb) - skb_network_header(skb);
+	if (unlikely(!mpls_hlen || mpls_hlen % MPLS_HLEN))
+		goto out;
 	if (unlikely(!pskb_may_pull(skb, mpls_hlen)))
 		goto out;
 
-- 
2.29.2