Re: [PATCH net V3] openvswitch: fix skb_panic due to the incorrect actions attrlen

From: Liping Zhang <redacted>
Date: Wed, 16 Aug 2017 13:30:07 +0800

From: Liping Zhang <redacted>

For sw_flow_actions, the actions_len only represents the kernel part's
size, and when we dump the actions to the userspace, we will do the
convertions, so it's true size may become bigger than the actions_len.

But unfortunately, for OVS_PACKET_ATTR_ACTIONS, we use the actions_len
to alloc the skbuff, so the user_skb's size may become insufficient and
oops will happen like this:

 ...

Also we can find that the actions_len is much little than the orig_len:
  crash> struct sw_flow_actions 0xffff8812f539d000
  struct sw_flow_actions {
    rcu = {
      next = 0xffff8812f5398800,
      func = 0xffffe3b00035db32
    },
    orig_len = 1384,
    actions_len = 592,
    actions = 0xffff8812f539d01c
  }

So as a quick fix, use the orig_len instead of the actions_len to alloc
the user_skb.

Last, this oops happened on our system running a relative old kernel, but
the same risk still exists on the mainline, since we use the wrong
actions_len from the beginning.

Fixes: ccea74457bbd ("openvswitch: include datapath actions with sampled-packet upcall to userspace")
Cc: Neil McKee <redacted>
Signed-off-by: Liping Zhang <redacted>

Applied and queued up for -stable, thanks.