Re: [PATCH net v2] nfc: nci: Fix uninit-value in nci_rx_work

[Simon Horman]

On Sat, Apr 27, 2024 at 07:35:54PM +0900, Ryosuke Yasuoka wrote:
> syzbot reported the following uninit-value access issue [1]
> 
> nci_rx_work() parses received packet from ndev->rx_q. It should be
> validated header size, payload size and total packet size before
> processing the packet. If an invalid packet is detected, it should be
> silently discarded.
> 
> Fixes: d24b03535e5e ("nfc: nci: Fix uninit-value in nci_dev_up and nci_ntf_packet")
> Reported-and-tested-by: syzbot+d7b4dc6cd50410152534@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=d7b4dc6cd50410152534 [1]
> Signed-off-by: Ryosuke Yasuoka <ryasuoka@xxxxxxxxxx>

..

> @@ -1516,30 +1526,36 @@ static void nci_rx_work(struct work_struct *work)
>  		nfc_send_to_raw_sock(ndev->nfc_dev, skb,
>  				     RAW_PAYLOAD_NCI, NFC_DIRECTION_RX);
>  
> -		if (!nci_plen(skb->data)) {
> -			kfree_skb(skb);
> -			break;
> -		}
> +		if (!skb->len)
> +			goto invalid_pkt_free;
>  
>  		/* Process frame */
>  		switch (nci_mt(skb->data)) {
>  		case NCI_MT_RSP_PKT:
> +			if (!nci_valid_size(skb, NCI_CTRL_HDR_SIZE))
> +				goto invalid_pkt_free;

Hi Yasuoka-san,

My reading is that this will jump to the label invalid_pkt_free,
which is intended.

>  			nci_rsp_packet(ndev, skb);
>  			break;

But this will exit the switch statement, which lands
at the label invalid_pkt_free, where skb is kfreed.
This doesn't seem to be intended.

>  
>  		case NCI_MT_NTF_PKT:
> +			if (!nci_valid_size(skb, NCI_CTRL_HDR_SIZE))
> +				goto invalid_pkt_free;
>  			nci_ntf_packet(ndev, skb);
>  			break;
>  
>  		case NCI_MT_DATA_PKT:
> +			if (!nci_valid_size(skb, NCI_DATA_HDR_SIZE))
> +				goto invalid_pkt_free;
>  			nci_rx_data_packet(ndev, skb);
>  			break;
>  
>  		default:
>  			pr_err("unknown MT 0x%x\n", nci_mt(skb->data));
> -			kfree_skb(skb);
> -			break;
> +			goto invalid_pkt_free;
>  		}

If so, then one solution may be to add the following here:

		continue;

> +invalid_pkt_free:
> +		kfree_skb(skb);
> +		break;
>  	}
>  
>  	/* check if a data exchange timeout has occurred */
> -- 
> 2.44.0
> 
>