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 <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. 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 ... > -- > > 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
