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

[ Upstream commit 9e1437937807b0122e8da1ca8765be2adca9aee6 ]

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 <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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index 35610cc881a9a388efa6081d16690efebe4b3614..c47660fba4988b4d5193928acd5f5879f3fe82d5 100644 (file)
--- 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 2fb7a78308e1a3e751b7d523dcc3eb9ae7b6ef9c..37c32e73aaef3c34c8040748b9e8b2940e13a9ed 100644 (file)
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2550,6 +2550,10 @@ 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)) {