@@ -3269,7 +3269,7 @@ decode_session4(struct sk_buff *skb, struct flowi *fl, bool reverse)
struct flowi4 *fl4 = &fl->u.ip4;
int oif = 0;
- if (skb_dst(skb))
+ if (skb_dst(skb) && skb_dst(skb)->dev)
oif = skb_dst(skb)->dev->ifindex;
memset(fl4, 0, sizeof(struct flowi4));
@@ -3387,7 +3387,7 @@ decode_session6(struct sk_buff *skb, struct flowi *fl, bool reverse)
nexthdr = nh[nhoff];
- if (skb_dst(skb))
+ if (skb_dst(skb) && skb_dst(skb)->dev)
oif = skb_dst(skb)->dev->ifindex;
memset(fl6, 0, sizeof(struct flowi6));
In decode_session{4,6} there is a possibility that the skb dst dev is NULL, e,g, with tunnel collect_md mode, which will cause kernel crash. Here is what the code path looks like, for GRE: - ip6gre_tunnel_xmit - ip6gre_xmit_ipv6 - __gre6_xmit - ip6_tnl_xmit - if skb->len - t->tun_hlen - eth_hlen > mtu; return -EMSGSIZE - icmpv6_send - icmpv6_route_lookup - xfrm_decode_session_reverse - decode_session4 - oif = skb_dst(skb)->dev->ifindex; <-- here - decode_session6 - oif = skb_dst(skb)->dev->ifindex; <-- here The reason is __metadata_dst_init() init dst->dev to NULL by default. We could not fix it in __metadata_dst_init() as there is no dev supplied. On the other hand, the skb_dst(skb)->dev is actually not needed as we called decode_session{4,6} via xfrm_decode_session_reverse(), so oif is not used by: fl4->flowi4_oif = reverse ? skb->skb_iif : oif; So make a dst dev check here should be clean and safe. Fixes: 8d79266bc48c ("ip6_tunnel: add collect_md mode to IPv6 tunnels") Signed-off-by: Hangbin Liu <liuhangbin@gmail.com> --- net/xfrm/xfrm_policy.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)