Re: [PATCH net v4 4/7] usbnet: ipheth: use static NDP16 location in URB

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Jan 05, 2025 at 02:01:18AM +0100, Foster Snowhill wrote:
> Original code allowed for the start of NDP16 to be anywhere within the
> URB based on the `wNdpIndex` value in NTH16. Only the start position of
> NDP16 was checked, so it was possible for even the fixed-length part
> of NDP16 to extend past the end of URB, leading to an out-of-bounds
> read.
> 
> On iOS devices, the NDP16 header always directly follows NTH16. Rely on
> and check for this specific format.
> 
> This, along with NCM-specific minimal URB length check that already
> exists, will ensure that the fixed-length part of NDP16 plus a set
> amount of DPEs fit within the URB.
> 
> Note that this commit alone does not fully address the OoB read.
> The limit on the amount of DPEs needs to be enforced separately.
> 
> Fixes: a2d274c62e44 ("usbnet: ipheth: add CDC NCM support")
> Signed-off-by: Foster Snowhill <forst@pen.gy>
> ---
> v4:
>     Additionally check that ncmh->wNdpIndex points immediately after
>     NTH16. This covers an unexpected on real devices, and highly
>     unlikely otherwise, case where the bytes after NTH16 are set to
>     `USB_CDC_NCM_NDP16_NOCRC_SIGN`, yet aren't the beginning of the
>     NDP16 header.
> v3: https://lore.kernel.org/netdev/20241123235432.821220-4-forst@pen.gy/
>     Split out from a monolithic patch in v2 as an atomic change.
> v2: https://lore.kernel.org/netdev/20240912211817.1707844-1-forst@pen.gy/
>     No code changes. Update commit message to further clarify that
>     `ipheth` is not and does not aim to be a complete or spec-compliant
>     CDC NCM implementation.
> v1: https://lore.kernel.org/netdev/20240907230108.978355-1-forst@pen.gy/
> ---
>  drivers/net/usb/ipheth.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
> index 48c79e69bb7b..35f507db2c4a 100644
> --- a/drivers/net/usb/ipheth.c
> +++ b/drivers/net/usb/ipheth.c
> @@ -237,15 +237,14 @@ static int ipheth_rcvbulk_callback_ncm(struct urb *urb)
>  
>  	ncmh = urb->transfer_buffer;
>  	if (ncmh->dwSignature != cpu_to_le32(USB_CDC_NCM_NTH16_SIGN) ||
> -	    le16_to_cpu(ncmh->wNdpIndex) >= urb->actual_length) {
> +	    /* On iOS, NDP16 directly follows NTH16 */
> +	    ncmh->wNdpIndex != cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16))) {
>  		dev->net->stats.rx_errors++;
>  		return retval;
>  	}
>  
> -	ncm0 = urb->transfer_buffer + le16_to_cpu(ncmh->wNdpIndex);
> -	if (ncm0->dwSignature != cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN) ||
> -	    le16_to_cpu(ncmh->wHeaderLength) + le16_to_cpu(ncm0->wLength) >=
> -	    urb->actual_length) {
> +	ncm0 = urb->transfer_buffer + sizeof(struct usb_cdc_ncm_nth16);
> +	if (ncm0->dwSignature != cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN)) {
>  		dev->net->stats.rx_errors++;
>  		return retval;
>  	}
> -- 
> 2.45.1
> 
> 

Hi,

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