RE: [PATCH net,v2 1/2] hv_netvsc: Fix offset usage in netvsc_send_table()

[Haiyang Zhang]

> -----Original Message-----
> From: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
> Sent: Thursday, November 21, 2019 6:05 PM
> To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> Cc: sashal@xxxxxxxxxx; linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx;
> KY Srinivasan <kys@xxxxxxxxxxxxx>; Stephen Hemminger
> <sthemmin@xxxxxxxxxxxxx>; olaf@xxxxxxxxx; vkuznets
> <vkuznets@xxxxxxxxxx>; davem@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH net,v2 1/2] hv_netvsc: Fix offset usage in
> netvsc_send_table()
> 
> On Thu, 21 Nov 2019 13:33:40 -0800, Haiyang Zhang wrote:
> > To reach the data region, the existing code adds offset in struct
> > nvsp_5_send_indirect_table on the beginning of this struct. But the
> > offset should be based on the beginning of its container,
> > struct nvsp_message. This bug causes the first table entry missing,
> > and adds an extra zero from the zero pad after the data region.
> > This can put extra burden on the channel 0.
> >
> > So, correct the offset usage. Also add a boundary check to ensure
> > not reading beyond data region.
> 
> Please provide a change log at the end of the commit message when
> posting new version in the future.
Sure. Will do that in the future.

> 
> > Fixes: 5b54dac856cb ("hyperv: Add support for virtual Receive Side Scaling
> (vRSS)")
> > Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> 
> >
> > -	tab = (u32 *)((unsigned long)&nvmsg->msg.v5_msg.send_table +
> > -		      nvmsg->msg.v5_msg.send_table.offset);
> > +	if (offset > msglen - count * sizeof(u32)) {
> 
> Can't this underflow now? What if msglen is small?
msglen came from the vmbus container message. We trust it to be big
enough for the data region.

Thanks,
- Haiyang