netdev - Re: [PATCH net] net: vxlan: fix crash when interface is created with no group

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Date:	Sun, 23 Mar 2014 22:09:33 -0700
From:	Pravin Shelar <pshelar@...ira.com>
To:	Mike Rapoport <mike.rapoport@...ellosystems.com>
Cc:	David Stevens <dlstevens@...ibm.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: vxlan: fix crash when interface is created with
 no group

On Sun, Mar 23, 2014 at 2:27 AM, Mike Rapoport
<mike.rapoport@...ellosystems.com> wrote:
> On Fri, Mar 21, 2014 at 05:22:06AM -0600, David Stevens wrote:
>> -----Mike Rapoport <mike.rapoport@...ellosystems.com> wrote: -----
>>
>> >Checking skb->protocol will drop ARP requests. What about using
>> >ip_hdr(skb)->version?
>>
>> Mike, ip_hdr() here is the outer packet, so it's got to be a UDP packet--
>> we just don't know if it's UDP/IP or UDP/IPv6 when it is bound to INADDR_ANY,
>> since both can be delivered. It could use version in this case, because
>> both possible protocols have version in the same place, but I think it's
>> more correct to use the MAC layer protocol rather than relying on the
>> fact that IPv4 and IPv6 have "version" in the same spot. "It could be ARP"
>> would be the argument for NOT using the version in places where it really
>> could be ARP, even though that isn't the case here.
>>
>> vxlan_rcv() is only called for VXLAN encapsulated packets sent to the bound
>> UDP port.
>>
>> So, if "vs->family" holds the one we want to support, we can't just blindly
>> assume the received packet is IPv4, for example, and start accessing
>> IPv4 fields, because it could be an IPv6 packet. We have to check the
>> packet type too. And if it's not the one we bound to, drop it.
>>
>> That's what the code snippet I outlined is trying to do.
>>
>>                                          +-DLS
>>
>
> I beleive I've groked what's going on in vxlan_udp_encap_recv and
> vxlan_rcv. There are actually two unrelated problems:
>
> 1) When the vxlan is configured with IPv4 group it crashes when it
> starts to receive IPv6 IGMP packets encapsulated into IPv4 vxlan
> packets. This happens because when ipv6_rcv handles the inner packet,
> the skb->dst still refernces outer IPv4 info. The very old vxlan code
> had skb_dst_drop call in vxlan_udp_encap_recv, which was removed when
> vxlan was refactored to use iptunnel_pull_header (commit
> 7ce04758279514ca1d8ebfe322508a4a430fe2c8: "vxlan: Restructure vxlan
> receive"). The iptunnel_pull_header called skb_dst_drop until recent
> commit 10ddceb22bab11dab10ba645c7df2e4a8e7a5db5 ("ip_tunnel:multicast
> process cause panic due to skb->_skb_refdst NULL pointer").
> The simplest fix, I think, would be to restore call to skb_dst_drop in
> vxlan_udp_encap_recv.
>
iptunnel_pull() is used in multiple tunnel implementation, therefore
we need drop dst in that function.
I send out fix : http://marc.info/?l=linux-netdev&m=139563761515707
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