netdev - Re: [PATCH net-next] net/vxlan: Avoid unaligned access in vxlan_build

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160920170742.GR8920@oracle.com>
Date:   Tue, 20 Sep 2016 13:07:42 -0400
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Jiri Benc <jbenc@...hat.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        hannes@...essinduktion.org, aduyck@...antis.com,
        daniel@...earbox.net, pabeni@...hat.com
Subject: Re: [PATCH net-next] net/vxlan: Avoid unaligned access in
 vxlan_build_skb()

On (09/20/16 18:43), Jiri Benc wrote:
> 
> IPv6 header is certainly not 20 bytes.

vxlan encapsulates an IPv6/ethernet frame in a UDP/IPv4/ethernet packet.
the ipv4 header is 20 bytes (without options).
mld_newpack is dealing with the vxlan net_device in this case,
which has ->hard_header_len of 14, and ->needed_headroom of 64,
so hlen (used in mld_newpack) comes out to be 80.

> If you see unaligned access, something is wrong. But I very much doubt
> that the problem is at the place you're trying to fix. Could you share
> the traces with us?

Exactly what traces do you want? I think you can check this easily
by using printk's predicated on IS_ALIGNED checks in vxlan_build_skb().
IPv6 MLD triggers this quite easily.

I will try out Hannes' solution (which makes sense) in a moment, 
and report back.

--Sowmini