[PATCH 5.4 052/111] xfrm: Fix NULL pointer dereference on policy lookup

From: Greg Kroah-Hartman
Date: Mon Apr 12 2021 - 04:53:47 EST

From: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>

[ Upstream commit b1e3a5607034aa0a481c6f69a6893049406665fb ]

When xfrm interfaces are used in combination with namespaces
and ESP offload, we get a dst_entry NULL pointer dereference.
This is because we don't have a dst_entry attached in the ESP
offloading case and we need to do a policy lookup before the
namespace transition.

Fix this by expicit checking of skb_dst(skb) before accessing it.

Fixes: f203b76d78092 ("xfrm: Add virtual xfrm interfaces")
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/net/xfrm.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index c00b9ae71ae4..614f19bbad74 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1098,7 +1098,7 @@ static inline int __xfrm_policy_check2(struct sock *sk, int dir,
return __xfrm_policy_check(sk, ndir, skb, family);

return (!net->xfrm.policy_count[dir] && !secpath_exists(skb)) ||
- (skb_dst(skb)->flags & DST_NOPOLICY) ||
+ (skb_dst(skb) && (skb_dst(skb)->flags & DST_NOPOLICY)) ||
__xfrm_policy_check(sk, ndir, skb, family);
}

--
2.30.2