ip_vti: fix potential slab-use-after-free in decode_session6

When ip_vti device is set to the qdisc of the sfb type, the cb field
of the sent skb may be modified during enqueuing. Then,
slab-use-after-free may occur when ip_vti device sends IPv6 packets.
As commit f855691975bb ("xfrm6: Fix the nexthdr offset in
_decode_session6.") showed, xfrm_decode_session was originally intended
only for the receive path. IP6CB(skb)->nhoff is not set during
transmission. Therefore, set the cb field in the skb to 0 before
sending packets.

Fixes: f855691975bb ("xfrm6: Fix the nexthdr offset in _decode_session6.")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index 53bfd8a..d1e7d0c 100644 (file)
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -287,12 +287,12 @@ static netdev_tx_t vti_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 
        switch (skb->protocol) {
        case htons(ETH_P_IP):
-               xfrm_decode_session(skb, &fl, AF_INET);
                memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
+               xfrm_decode_session(skb, &fl, AF_INET);
                break;
        case htons(ETH_P_IPV6):
-               xfrm_decode_session(skb, &fl, AF_INET6);
                memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
+               xfrm_decode_session(skb, &fl, AF_INET6);
                break;
        default:
                goto tx_err;