On Tue, Feb 15, 2022 at 11:35:47AM +0100, Oliver Neukum wrote:
> A broken device may give an extreme offset like 0xFFF0
> and a reasonable length for a fragment. In the sanity
> check as formulated now, this will create an integer
> overflow, defeating the sanity check. Both offset
> and offset + len need to be checked in such a manner
> that no overflow can occur.
> And those quantities should be unsigned.
>
> Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
> ---
> drivers/net/usb/cdc_ncm.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
> index e303b522efb5..15f91d691bba 100644
> --- a/drivers/net/usb/cdc_ncm.c
> +++ b/drivers/net/usb/cdc_ncm.c
> @@ -1715,10 +1715,10 @@ int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
> {
> struct sk_buff *skb;
> struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
> - int len;
> + unsigned int len;
> int nframes;
> int x;
> - int offset;
> + unsigned int offset;
> union {
> struct usb_cdc_ncm_ndp16 *ndp16;
> struct usb_cdc_ncm_ndp32 *ndp32;
> @@ -1790,8 +1790,8 @@ int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
> break;
> }
>
> - /* sanity checking */
> - if (((offset + len) > skb_in->len) ||
> + /* sanity checking - watch out for integer wrap*/
> + if ((offset > skb_in->len) || (len > skb_in->len - offset) ||
> (len > ctx->rx_max) || (len < ETH_HLEN)) {
> netif_dbg(dev, rx_err, dev->net,
> "invalid frame detected (ignored) offset[%u]=%u, length=%u, skb=%p\n",
> --
> 2.34.1
>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
