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Date:   Wed,  7 Oct 2020 18:21:54 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        syzbot+4a2c52677a8a1aa283cb@...kaller.appspotmail.com,
        William Tu <u9012063@...il.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: [Patch net] ip_gre: set dev->hard_header_len properly

GRE tunnel has its own header_ops, ipgre_header_ops, and sets it
conditionally. When it is set, it assumes the outer IP header is
already created before ipgre_xmit().

This is not true when we send packets through a raw packet socket,
where L2 headers are supposed to be constructed by user. Packet
socket calls dev_validate_header() to validate the header. But
GRE tunnel does not set dev->hard_header_len, so that check can
be simply bypassed, therefore uninit memory could be passed down
to ipgre_xmit().

Fix this by setting dev->hard_header_len whenever sets header_ops,
as dev->hard_header_len is supposed to be the length of the header
created by dev->header_ops->create() anyway.

Reported-and-tested-by: syzbot+4a2c52677a8a1aa283cb@...kaller.appspotmail.com
Cc: William Tu <u9012063@...il.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/ipv4/ip_gre.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 4e31f23e4117..43b62095559e 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -987,10 +987,12 @@ static int ipgre_tunnel_init(struct net_device *dev)
 				return -EINVAL;
 			dev->flags = IFF_BROADCAST;
 			dev->header_ops = &ipgre_header_ops;
+			dev->hard_header_len = tunnel->hlen + sizeof(*iph);
 		}
 #endif
 	} else if (!tunnel->collect_md) {
 		dev->header_ops = &ipgre_header_ops;
+		dev->hard_header_len = tunnel->hlen + sizeof(*iph);
 	}
 
 	return ip_tunnel_init(dev);
-- 
2.28.0

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