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From:   gregkh@linuxfoundation.org
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Balazs Nemeth <bnemeth@redhat.com>,
        Willem de Bruijn <willemb@google.com>,
        David Ahern <dsahern@kernel.org>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.19 019/120] net: avoid infinite loop in mpls_gso_segment when mpls_hlen == 0
Date:   Mon, 15 Mar 2021 14:56:10 +0100
Message-Id: <20210315135720.638602447@linuxfoundation.org>
In-Reply-To: <20210315135720.002213995@linuxfoundation.org>
References: <20210315135720.002213995@linuxfoundation.org>
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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

From: Balazs Nemeth <bnemeth@redhat.com>

commit d348ede32e99d3a04863e9f9b28d224456118c27 upstream.

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>
Acked-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/mpls/mpls_gso.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/mpls/mpls_gso.c
+++ b/net/mpls/mpls_gso.c
@@ -18,6 +18,7 @@
 #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)
@@ -31,6 +32,8 @@ static struct sk_buff *mpls_gso_segment(
 
 	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;