tree 0c97d1dc87bf2b54971bf0b215ddbd5a837a9fb5
parent ca92e173ab34a4f7fc4128bd372bd96f1af6f507
author Steffen Klassert <steffen.klassert@secunet.com> 1542867984 +0100
committer Steffen Klassert <steffen.klassert@secunet.com> 1542877779 +0100

xfrm: Fix NULL pointer dereference in xfrm_input 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 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>