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 <rusty@xxxxxxxxxxxxxxx> > > Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> > > Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx > > Cc: netdev@xxxxxxxxxxxxxxx > > Cc: kvm@xxxxxxxxxxxxxxx > > Signed-off-by: Sasha Levin <levinsasha928@xxxxxxxxx> > > 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. -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
