[PATCH net-next] net/mpls: fix WARNING in mpls_gso_segment

[Lizhi Xu]

When the network header pointer is greater than the inner network header, the
difference between the two can cause mpls_hlen overflow.

Reported-and-tested-by: syzbot+99d15fcdb0132a1e1a82@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
---
 net/mpls/mpls_gso.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/mpls/mpls_gso.c b/net/mpls/mpls_gso.c
index 533d082f0701..2ab24b2fd90f 100644
--- a/net/mpls/mpls_gso.c
+++ b/net/mpls/mpls_gso.c
@@ -25,11 +25,11 @@ static struct sk_buff *mpls_gso_segment(struct sk_buff *skb,
 	netdev_features_t mpls_features;
 	u16 mac_len = skb->mac_len;
 	__be16 mpls_protocol;
-	unsigned int mpls_hlen;
+	int mpls_hlen;
 
 	skb_reset_network_header(skb);
 	mpls_hlen = skb_inner_network_header(skb) - skb_network_header(skb);
-	if (unlikely(!mpls_hlen || mpls_hlen % MPLS_HLEN))
+	if (unlikely(mpls_hlen <= 0 || mpls_hlen % MPLS_HLEN))
 		goto out;
 	if (unlikely(!pskb_may_pull(skb, mpls_hlen)))
 		goto out;
-- 
2.43.0