[PATCH 5.4 36/92] erspan: fix version 1 check in gre_parse_header()

From: Cong Wang <redacted>

[ Upstream commit 085c7c4e1c0e50d90b7d90f61a12e12b317a91e2 ]

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 <redacted>
Cc: Lorenzo Bianconi <redacted>
Signed-off-by: Cong Wang <redacted>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/gre_demux.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c

@@ -128,7 +128,7 @@ int gre_parse_header(struct sk_buff *skb
 	 * 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;