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    SubjectRe: [PATCH v2 1/2] virtio-net: Verify page list size before fitting into skb
    On Wed, Oct 05, 2011 at 03:50:54PM +0200, Sasha Levin wrote:
    > On Mon, 2011-10-03 at 21:04 +0200, Michael S. Tsirkin wrote:
    > > On Wed, Sep 28, 2011 at 05:40:54PM +0300, Sasha Levin wrote:
    > > > This patch verifies that the length of a buffer stored in a linked list
    > > > of pages is small enough to fit into a skb.
    > > >
    > > > If the size is larger than a max size of a skb, it means that we shouldn't
    > > > go ahead building skbs anyway since we won't be able to send the buffer as
    > > > the user requested.
    > > >
    > > > Cc: Rusty Russell <rusty@rustcorp.com.au>
    > > > Cc: "Michael S. Tsirkin" <mst@redhat.com>
    > > > Cc: virtualization@lists.linux-foundation.org
    > > > Cc: netdev@vger.kernel.org
    > > > Cc: kvm@vger.kernel.org
    > > > Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
    > > > ---
    > > > drivers/net/virtio_net.c | 13 +++++++++++++
    > > > 1 files changed, 13 insertions(+), 0 deletions(-)
    > > >
    > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
    > > > index 0c7321c..bde0dec 100644
    > > > --- a/drivers/net/virtio_net.c
    > > > +++ b/drivers/net/virtio_net.c
    > > > @@ -195,6 +195,19 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
    > > > len -= copy;
    > > > offset += copy;
    > > >
    > > > + /*
    > > > + * Verify that we can indeed put this data into a skb.
    > > > + * This is here to handle cases when the device erroneously
    > > > + * tries to receive more than is possible. This is usually
    > > > + * the case of a broken device.
    > > > + */
    > > > + if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) {
    > > > + if (net_ratelimit())
    > > > + pr_debug("%s: too much data\n", skb->dev->name);
    > > > + dev_kfree_skb(skb);
    > > > + return NULL;
    > > > + }
    > > > +
    > >
    > > BTW, receive_mergeable does
    > > pr_debug("%s: packet too long\n", skb->dev->name);
    > > skb->dev->stats.rx_length_errors++;
    > >
    > > which makes sense.
    >
    > Do you think we should increase rx_length_errors here as well?

    this is all debugging tool for devices/drivers, right?
    so maybe not worth the noise.

    > --
    >
    > Sasha.


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