[PATCH] net/xfrm: Fix lookups for states with spi == 0

[Dmitry Safonov]

It seems to be a valid use case to add xfrm state without
Security Parameter Indexes (SPI) value associated:
ip xfrm state add src $src dst $dst proto $proto mode $mode sel src $src dst $dst $algo

The bad thing is that it's currently impossible to get/delete the state
without SPI: __xfrm_state_insert() obviously doesn't add hash for zero
SPI in xfrm.state_byspi, and xfrm_user_state_lookup() will fail as
xfrm_state_lookup() does lookups by hash.

It also isn't possible to workaround from userspace as
xfrm_id_proto_match() will be always true for ah/esp/comp protos.

So, don't try looking up by hash if SPI == 0.

Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
---
 net/xfrm/xfrm_user.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 080035f056d9..6b38503255c8 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -681,7 +681,7 @@ static struct xfrm_state *xfrm_user_state_lookup(struct net *net,
 	int err;
 	u32 mark = xfrm_mark_get(attrs, &m);
 
-	if (xfrm_id_proto_match(p->proto, IPSEC_PROTO_ANY)) {
+	if (xfrm_id_proto_match(p->proto, IPSEC_PROTO_ANY) && p->spi) {
 		err = -ESRCH;
 		x = xfrm_state_lookup(net, mark, &p->daddr, p->spi, p->proto, p->family);
 	} else {
-- 
2.13.6