Subject: Re: [PATCH v4 net] net: hv_netvsc: fix netvsc_send_completion to avoid multiple message length checks

From: Simon Horman <[email-masked]>
Date: Sun, 10 Sep 2023 16:01:35 +0200

On Thu, Sep 07, 2023 at 12:56:47PM -0700, Sonia Sharma wrote:
> From: Sonia Sharma <[email-masked]>
> 
> The switch statement in netvsc_send_completion() is incorrectly validating
> the length of incoming network packets by falling through to the next case.
> Avoid the fallthrough. Instead break after a case match and then process
> the complete() call.
> The current code has not caused any known failures. But nonetheless, the
> code should be corrected as a different ordering of the switch cases might
> cause a length check to fail when it should not.
> 
> Fixes: 44144185951a0f ("hv_netvsc: Add validation for untrusted Hyper-V values")

As the current code is correct - it works - I feel that this is more of a
clean-up than a fix. As such I suggest dropping the fixes tag and
retargeting at net-next (which is due to re-open in the coming days).

> Signed-off-by: Sonia Sharma <[email-masked]>
> 
> ---
> Changes in v3:
> * added return statement in default case as pointed by Michael Kelley.
> Changes in v4:
> * added fixes tag
> * modified commit message to explain the issue fixed by patch.
> ---
>  drivers/net/hyperv/netvsc.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
> index 82e9796c8f5e..0f7e4d377776 100644
> --- a/drivers/net/hyperv/netvsc.c
> +++ b/drivers/net/hyperv/netvsc.c
> @@ -851,7 +851,7 @@ static void netvsc_send_completion(struct net_device *ndev,
>  				   msglen);
>  			return;
>  		}
> -		fallthrough;
> +		break;
>  
>  	case NVSP_MSG1_TYPE_SEND_RECV_BUF_COMPLETE:
>  		if (msglen < sizeof(struct nvsp_message_header) +
> @@ -860,7 +860,7 @@ static void netvsc_send_completion(struct net_device *ndev,
>  				   msglen);
>  			return;
>  		}
> -		fallthrough;
> +		break;
>  
>  	case NVSP_MSG1_TYPE_SEND_SEND_BUF_COMPLETE:
>  		if (msglen < sizeof(struct nvsp_message_header) +
> @@ -869,7 +869,7 @@ static void netvsc_send_completion(struct net_device *ndev,
>  				   msglen);
>  			return;
>  		}
> -		fallthrough;
> +		break;
>  
>  	case NVSP_MSG5_TYPE_SUBCHANNEL:
>  		if (msglen < sizeof(struct nvsp_message_header) +
> @@ -878,10 +878,6 @@ static void netvsc_send_completion(struct net_device *ndev,
>  				   msglen);
>  			return;
>  		}
> -		/* Copy the response back */
> -		memcpy(&net_device->channel_init_pkt, nvsp_packet,
> -		       sizeof(struct nvsp_message));
> -		complete(&net_device->channel_init_wait);
>  		break;
>  
>  	case NVSP_MSG1_TYPE_SEND_RNDIS_PKT_COMPLETE:
> @@ -904,13 +900,19 @@ static void netvsc_send_completion(struct net_device *ndev,
>  
>  		netvsc_send_tx_complete(ndev, net_device, incoming_channel,
>  					desc, budget);
> -		break;
> +		return;
>  
>  	default:
>  		netdev_err(ndev,
>  			   "Unknown send completion type %d received!!\n",
>  			   nvsp_packet->hdr.msg_type);
> +		return;
>  	}
> +
> +	/* Copy the response back */
> +	memcpy(&net_device->channel_init_pkt, nvsp_packet,
> +			sizeof(struct nvsp_message));

nit: the indentation of the line above is not correct.

	memcpy(&net_device->channel_init_pkt, nvsp_packet,
	       sizeof(struct nvsp_message));

> +	complete(&net_device->channel_init_wait);
>  }
>  
>  static u32 netvsc_get_next_send_section(struct netvsc_device *net_device)
> -- 
> 2.25.1
> 
>