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

[ Upstream commit 0152eee6fc3b84298bb6a79961961734e8afa5b8 ]

Since commit 222d7dbd258d ("net: prevent dst uses after free")
skb_dst_force() might clear the dst_entry attached to the skb.
The xfrm code doesn'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 case the dst_entry was cleared. We also
move the skb_dst_force() to a codepath that is not used when
the transformation was offloaded, because in this case we
don't have a dst_entry attached to the skb.

The output and forwarding path was already fixed by
commit 9e1437937807 ("xfrm: Fix NULL pointer dereference when
skb_dst_force clears the dst_entry.")

Fixes: 222d7dbd258d ("net: prevent dst uses after free")
Reported-by: Jean-Philippe Menil <jpmenil@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 8e75319..06dec32 100644 (file)
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -341,6 +341,12 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 
                skb->sp->xvec[skb->sp->len++] = x;
 
+               skb_dst_force(skb);
+               if (!skb_dst(skb)) {
+                       XFRM_INC_STATS(net, LINUX_MIB_XFRMINERROR);
+                       goto drop;
+               }
+
 lock:
                spin_lock(&x->lock);
 
@@ -380,7 +386,6 @@ lock:
                XFRM_SKB_CB(skb)->seq.input.low = seq;
                XFRM_SKB_CB(skb)->seq.input.hi = seq_hi;
 
-               skb_dst_force(skb);
                dev_hold(skb->dev);
 
                if (crypto_done)