[Patch net] erspan: fix version 1 check in gre_parse_header()

[Cong Wang <xiyou.wangcong@gmail.com>]

From: Cong Wang <cong.wang@bytedance.com>

Both version 0 and version 1 use ETH_P_ERSPAN, but version 0 does not
have an erspan header. So the check in gre_parse_header() is wrong,
we have to distinguish version 1 from version 0.

We can just check the gre header length like is_erspan_type1().

Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
Reported-by: syzbot+f583ce3d4ddf9836b27a@syzkaller.appspotmail.com
Cc: William Tu <u9012063@gmail.com>
Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
---
 net/ipv4/gre_demux.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
index 66fdbfe5447c..5d1e6fe9d838 100644
--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c
@@ -128,7 +128,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 	 * to 0 and sets the configured key in the
 	 * inner erspan header field
 	 */
-	if (greh->protocol == htons(ETH_P_ERSPAN) ||
+	if ((greh->protocol == htons(ETH_P_ERSPAN) && hdr_len != 4) ||
 	    greh->protocol == htons(ETH_P_ERSPAN2)) {
 		struct erspan_base_hdr *ershdr;
 
-- 
2.25.1