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

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Date:   Wed, 16 Aug 2017 12:21:17 -0700
From:   Pravin Shelar <pshelar@....org>
To:     Liping Zhang <zlpnobody@....com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Liping Zhang <zlpnobody@...il.com>,
        Neil McKee <neil.mckee@...on.com>
Subject: Re: [PATCH net V3] openvswitch: fix skb_panic due to the incorrect
 actions attrlen

On Tue, Aug 15, 2017 at 10:30 PM, Liping Zhang <zlpnobody@....com> wrote:
> From: Liping Zhang <zlpnobody@...il.com>
>
> 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:
>   skbuff: skb_over_panic: text:ffffffff8148fabf len:1749 put:157 head:
>   ffff881300f39000 data:ffff881300f39000 tail:0x6d5 end:0x6c0 dev:<NULL>
>   ------------[ cut here ]------------
>   kernel BUG at net/core/skbuff.c:129!
>   [...]
>   Call Trace:
>    <IRQ>
>    [<ffffffff8148be82>] skb_put+0x43/0x44
>    [<ffffffff8148fabf>] skb_zerocopy+0x6c/0x1f4
>    [<ffffffffa0290d36>] queue_userspace_packet+0x3a3/0x448 [openvswitch]
>    [<ffffffffa0292023>] ovs_dp_upcall+0x30/0x5c [openvswitch]
>    [<ffffffffa028d435>] output_userspace+0x132/0x158 [openvswitch]
>    [<ffffffffa01e6890>] ? ip6_rcv_finish+0x74/0x77 [ipv6]
>    [<ffffffffa028e277>] do_execute_actions+0xcc1/0xdc8 [openvswitch]
>    [<ffffffffa028e3f2>] ovs_execute_actions+0x74/0x106 [openvswitch]
>    [<ffffffffa0292130>] ovs_dp_process_packet+0xe1/0xfd [openvswitch]
>    [<ffffffffa0292b77>] ? key_extract+0x63c/0x8d5 [openvswitch]
>    [<ffffffffa029848b>] ovs_vport_receive+0xa1/0xc3 [openvswitch]
>   [...]
>
> 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 <neil.mckee@...on.com>
> Signed-off-by: Liping Zhang <zlpnobody@...il.com>

Looks good.
Acked-by: Pravin B Shelar <pshelar@....org>