On Tue, Sep 27, 2011 at 09:44:02AM +0300, Sasha Levin wrote: > On Mon, 2011-09-26 at 22:55 +0300, Michael S. Tsirkin wrote: > > On Mon, Sep 26, 2011 at 10:37:22PM +0300, Sasha Levin wrote: > > > On Mon, 2011-09-26 at 21:44 +0300, Michael S. Tsirkin wrote: > > > > On Mon, Sep 26, 2011 at 08:41:08PM +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 <ru...@rustcorp.com.au> > > > > > Cc: "Michael S. Tsirkin" <m...@redhat.com> > > > > > Cc: virtualizat...@lists.linux-foundation.org > > > > > Cc: net...@vger.kernel.org > > > > > Cc: kvm@vger.kernel.org > > > > > Signed-off-by: Sasha Levin <levinsasha...@gmail.com> > > > > > > > > Interesting. This is a theoretical issue, correct? > > > > Not a crash you actually see. > > > > > > Actually it was an actual crash caused when our virtio-net driver in kvm > > > tools did funny things and passed '(u32)-1' length as a buffer length to > > > the guest kernel. > > > > > > > This crash would mean device is giving us packets > > > > that are way too large. Avoiding crashes even in the face of > > > > a misbehaved device is a good idea, but should > > > > we print a diagnostic to a system log? > > > > Maybe rate-limited or print once to avoid filling > > > > up the disk. Other places in driver print with pr_debug > > > > I'm not sure that's right but better than nothing. > > > > > > Yup, I'll add some debug info. > > > > > > > > --- > > > > > drivers/net/virtio_net.c | 3 +++ > > > > > 1 files changed, 3 insertions(+), 0 deletions(-) > > > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > > index 0c7321c..64e0717 100644 > > > > > --- a/drivers/net/virtio_net.c > > > > > +++ b/drivers/net/virtio_net.c > > > > > @@ -165,6 +165,9 @@ static struct sk_buff *page_to_skb(struct > > > > > virtnet_info *vi, > > > > > unsigned int copy, hdr_len, offset; > > > > > char *p; > > > > > > > > > > + if (len > MAX_SKB_FRAGS * PAGE_SIZE) > > > > > > > > unlikely()? > > > > > > > > Also, this seems too aggressive: at this point len includes the header > > > > and the linear part. The right place for this > > > > test is probably where we fill in the frags, just before > > > > while (len) > > > > > > > > The whole can only happen when mergeable buffers > > > > are disabled, right? > > > > > > >From what I understand it can happen whenever you're going to build a > > > skb longer than PAGE_SIZE. > > > > Hmm how exactly? With mergeable buffers this only gets > > the length of the 1st chunk which is up to 4K unless the driver > > is buggy ... > > What about the case where TSO or ECN features are set? The code flow > suggests that mergeable would get ignored in that case: > > /* If we can receive ANY GSO packets, we must allocate large ones. */ > if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) || > virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) || > virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN)) > vi->big_packets = true; > > [...] > > if (!vi->mergeable_rx_bufs && !vi->big_packets) { > skb = buf; > len -= sizeof(struct virtio_net_hdr); > skb_trim(skb, len); > } else { > page = buf; > skb = page_to_skb(vi, page, len); > ...
Sorry I don't get it yet. Where is mergeable ignored here? > I haven't actually tested it with mergeable buffers enabled, but could > do it later today. Please do. > -- > > Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html