From: "Michael S. Tsirkin" <mst@redhat.com>
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: netdev@vger.kernel.org, davem@davemloft.net,
Willem de Bruijn <willemb@google.com>
Subject: Re: [PATCH net] net/packet: tpacket_rcv: do not increment ring index on drop
Date: Tue, 10 Mar 2020 02:43:05 -0400 [thread overview]
Message-ID: <20200310023528-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20200309153435.32109-1-willemdebruijn.kernel@gmail.com>
On Mon, Mar 09, 2020 at 11:34:35AM -0400, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
>
> In one error case, tpacket_rcv drops packets after incrementing the
> ring producer index.
>
> If this happens, it does not update tp_status to TP_STATUS_USER and
> thus the reader is stalled for an iteration of the ring, causing out
> of order arrival.
>
> The only such error path is when virtio_net_hdr_from_skb fails due
> to encountering an unknown GSO type.
>
> Signed-off-by: Willem de Bruijn <willemb@google.com>
>
> ---
>
> I wonder whether it should drop packets with unknown GSO types at all.
> This consistently blinds the reader to certain packets, including
> recent UDP and SCTP GSO types.
Ugh it looks like you have found a bug. Consider a legacy userspace -
it was actually broken by adding USD and SCTP GSO. I suspect the right
thing to do here is actually to split these packets up, not drop them.
> The peer function virtio_net_hdr_to_skb already drops any packets with
> unknown types, so it should be fine to add an SKB_GSO_UNKNOWN type and
> let the peer at least be aware of failure.
>
> And possibly add SKB_GSO_UDP_L4 and SKB_GSO_SCTP types to virtio too.
This last one is possible for sure, but for virtio_net_hdr_from_skb
we'll need more flags to know whether it's safe to pass
these types to userspace.
> ---
> net/packet/af_packet.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 30c6879d6774..e5b0986215d2 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2274,6 +2274,13 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
> TP_STATUS_KERNEL, (macoff+snaplen));
> if (!h.raw)
> goto drop_n_account;
> +
> + if (do_vnet &&
> + virtio_net_hdr_from_skb(skb, h.raw + macoff -
> + sizeof(struct virtio_net_hdr),
> + vio_le(), true, 0))
> + goto drop_n_account;
> +
> if (po->tp_version <= TPACKET_V2) {
> packet_increment_rx_head(po, &po->rx_ring);
> /*
> @@ -2286,12 +2293,6 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
> status |= TP_STATUS_LOSING;
> }
>
> - if (do_vnet &&
> - virtio_net_hdr_from_skb(skb, h.raw + macoff -
> - sizeof(struct virtio_net_hdr),
> - vio_le(), true, 0))
> - goto drop_n_account;
> -
> po->stats.stats1.tp_packets++;
> if (copy_skb) {
> status |= TP_STATUS_COPY;
> --
> 2.25.1.481.gfbce0eb801-goog
next prev parent reply other threads:[~2020-03-10 6:43 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-09 15:34 [PATCH net] net/packet: tpacket_rcv: do not increment ring index on drop Willem de Bruijn
2020-03-09 15:42 ` Willem de Bruijn
2020-03-09 15:50 ` Willem de Bruijn
2020-03-10 6:46 ` Michael S. Tsirkin
2020-03-10 6:43 ` Michael S. Tsirkin [this message]
2020-03-10 12:49 ` Willem de Bruijn
2020-03-10 12:59 ` Michael S. Tsirkin
2020-03-10 14:16 ` Willem de Bruijn
2020-03-10 14:43 ` Michael S. Tsirkin
2020-03-10 15:38 ` Willem de Bruijn
2020-03-10 16:14 ` Willem de Bruijn
2020-03-10 21:29 ` Michael S. Tsirkin
2020-03-10 21:35 ` Willem de Bruijn
2020-03-10 21:57 ` Michael S. Tsirkin
2020-03-10 23:13 ` Willem de Bruijn
2020-03-11 7:56 ` Michael S. Tsirkin
2020-03-11 14:31 ` Willem de Bruijn
2020-03-11 21:25 ` Michael S. Tsirkin
2020-03-11 21:49 ` Willem de Bruijn
2020-03-12 6:13 ` David Miller
2020-03-12 6:27 ` Michael S. Tsirkin
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