netdev - Re: [PATCH net v3] virtio_net: fix wrong buf address calculation when using xdp

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Date:   Mon, 25 Apr 2022 15:10:33 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Nikolay Aleksandrov <razor@...ckwall.org>, netdev@...r.kernel.org
Cc:     kuba@...nel.org, davem@...emloft.net, stable@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net v3] virtio_net: fix wrong buf address calculation when
 using xdp

On 4/25/22 12:37 PM, Nikolay Aleksandrov wrote:
> We received a report[1] of kernel crashes when Cilium is used in XDP
> mode with virtio_net after updating to newer kernels. After
> investigating the reason it turned out that when using mergeable bufs
> with an XDP program which adjusts xdp.data or xdp.data_meta page_to_buf()
> calculates the build_skb address wrong because the offset can become less
> than the headroom so it gets the address of the previous page (-X bytes
> depending on how lower offset is):
>   page_to_skb: page addr ffff9eb2923e2000 buf ffff9eb2923e1ffc offset 252 headroom 256
[...]
> CC: stable@...r.kernel.org
> CC: Jason Wang <jasowang@...hat.com>
> CC: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> CC: Daniel Borkmann <daniel@...earbox.net>
> CC: "Michael S. Tsirkin" <mst@...hat.com>
> CC: virtualization@...ts.linux-foundation.org
> Fixes: 8fb7da9e9907 ("virtio_net: get build_skb() buf by data ptr")
> Signed-off-by: Nikolay Aleksandrov <razor@...ckwall.org>

Thanks everyone!

Acked-by: Daniel Borkmann <daniel@...earbox.net>