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Date:   Mon, 12 Oct 2020 18:56:32 -0700
From:   Xie He <>
To:     Cong Wang <>
Cc:     Linux Kernel Network Developers <>,
        syzbot <>,
        William Tu <>,
        Willem de Bruijn <>
Subject: Re: [Patch net v3] ip_gre: set dev->hard_header_len and
 dev->needed_headroom properly

On Mon, Oct 12, 2020 at 4:17 PM Cong Wang <> wrote:
> GRE tunnel has its own header_ops, ipgre_header_ops, and sets it
> conditionally. When it is set, it assumes the outer IP header is
> already created before ipgre_xmit().
> This is not true when we send packets through a raw packet socket,
> where L2 headers are supposed to be constructed by user. Packet
> socket calls dev_validate_header() to validate the header. But
> GRE tunnel does not set dev->hard_header_len, so that check can
> be simply bypassed, therefore uninit memory could be passed down
> to ipgre_xmit(). Similar for dev->needed_headroom.
> dev->hard_header_len is supposed to be the length of the header
> created by dev->header_ops->create(), so it should be used whenever
> header_ops is set, and dev->needed_headroom should be used when it
> is not set.

Acked-by: Xie He <>

Thank you for your work, Cong!

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