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 <liuhang...@gmail.com>
---
net/xfrm/xfrm_policy.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 8ca637a72697..ec94f5795ea4 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -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));
--
2.19.2
