From 9e1437937807b0122e8da1ca8765be2adca9aee6 Mon Sep 17 00:00:00 2001 From: Steffen Klassert Date: Tue, 11 Sep 2018 10:31:15 +0200 Subject: [PATCH] xfrm: Fix NULL pointer dereference when skb_dst_force clears the dst_entry. Since commit 222d7dbd258d ("net: prevent dst uses after free") skb_dst_force() might clear the dst_entry attached to the skb. The xfrm code don't expect this to happen, so we crash with a NULL pointer dereference in this case. Fix it by checking skb_dst(skb) for NULL after skb_dst_force() and drop the packet in cast the dst_entry was cleared. Fixes: 222d7dbd258d ("net: prevent dst uses after free") Reported-by: Tobias Hommel Reported-by: Kristian Evensen Reported-by: Wolfgang Walter Signed-off-by: Steffen Klassert --- net/xfrm/xfrm_output.c | 4 ++++ net/xfrm/xfrm_policy.c | 4 ++++ 2 files changed, 8 insertions(+) diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c index 89b178a78dc7..36d15a38ce5e 100644 --- a/net/xfrm/xfrm_output.c +++ b/net/xfrm/xfrm_output.c @@ -101,6 +101,10 @@ static int xfrm_output_one(struct sk_buff *skb, int err) spin_unlock_bh(&x->lock); skb_dst_force(skb); + if (!skb_dst(skb)) { + XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTERROR); + goto error_nolock; + } if (xfrm_offload(skb)) { x->type_offload->encap(x, skb); diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c index 7c5e8978aeaa..626e0f4d1749 100644 --- a/net/xfrm/xfrm_policy.c +++ b/net/xfrm/xfrm_policy.c @@ -2548,6 +2548,10 @@ int __xfrm_route_forward(struct sk_buff *skb, unsigned short family) } skb_dst_force(skb); + if (!skb_dst(skb)) { + XFRM_INC_STATS(net, LINUX_MIB_XFRMFWDHDRERROR); + return 0; + } dst = xfrm_lookup(net, skb_dst(skb), &fl, NULL, XFRM_LOOKUP_QUEUE); if (IS_ERR(dst)) {