netdev - Re: [PATCH net,v2 1/2] hv_netvsc: Fix offset usage in netvsc_send

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Date:   Thu, 21 Nov 2019 15:04:45 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Haiyang Zhang <haiyangz@...rosoft.com>
Cc:     sashal@...nel.org, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, kys@...rosoft.com, sthemmin@...rosoft.com,
        olaf@...fle.de, vkuznets@...hat.com, davem@...emloft.net,
        linux-kernel@...r.kernel.org
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.

> Fixes: 5b54dac856cb ("hyperv: Add support for virtual Receive Side Scaling (vRSS)")
> Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>

>  
> -	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?

> +		netdev_err(ndev, "Received send-table offset too big:%u\n",
> +			   offset);
> +		return;
> +	}
> +
> +	tab = (void *)nvmsg + offset;
>  
>  	for (i = 0; i < count; i++)
>  		net_device_ctx->tx_table[i] = tab[i];