Commit 9e143793 authored Sep 11, 2018 by Steffen Klassert

xfrm: Fix NULL pointer dereference when skb_dst_force clears the dst_entry.



Since commit 222d7dbd ("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: 222d7dbd ("net: prevent dst uses after free")
Reported-by: Tobias Hommel <netdev-list@genoetigt.de>
Reported-by: Kristian Evensen <kristian.evensen@gmail.com>
Reported-by: Wolfgang Walter <linux@stwm.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

parent 782710e3

net/xfrm/xfrm_output.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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);

net/xfrm/xfrm_policy.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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)) {

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