netdev - Re: [net-next PATCH] bpf: reserve xdp

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Date:   Thu, 19 Apr 2018 17:55:20 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [net-next PATCH] bpf: reserve xdp_frame size in xdp headroom

On 04/19/2018 04:17 PM, Jesper Dangaard Brouer wrote:
> Commit 6dfb970d3dbd ("xdp: avoid leaking info stored in frame data on
> page reuse") tried to allow user/bpf_prog to (re)use area used by
> xdp_frame (stored in frame headroom), by memset clearing area when
> bpf_xdp_adjust_head give bpf_prog access to headroom area.
> 
> The mentioned commit had two bugs. (1) Didn't take bpf_xdp_adjust_meta
> into account. (2) a combination of bpf_xdp_adjust_head calls, where
> xdp->data is moved into xdp_frame section, can cause clearing
> xdp_frame area again for area previously granted to bpf_prog.
> 
> After discussions with Daniel, we choose to implement a simpler
> solution to the problem, which is to reserve the headroom used by
> xdp_frame info.
> 
> This also avoids the situation where bpf_prog is allowed to adjust/add
> headers, and then XDP_REDIRECT later drops the packet due to lack of
> headroom for the xdp_frame.  This would likely confuse the end-user.
> 
> Fixes: 6dfb970d3dbd ("xdp: avoid leaking info stored in frame data on page reuse")
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>

Applied to bpf-next, thanks Jesper!