netdev - Re: possible integer overflow in CDC-NCM checks

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Date:   Thu, 10 Feb 2022 16:49:28 +0100
From:   Bjørn Mork <bjorn@...k.no>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     USB list <linux-usb@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: possible integer overflow in CDC-NCM checks

Oliver Neukum <oneukum@...e.com> writes:

> CDC-NCM: avoid overflow in sanity checking 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. It needs to be rewritten as a
> subtraction and the variables should be unsigned. Signed-off-by: Oliver
> Neukum <oneukum@...e.com> --- drivers/net/usb/cdc_ncm.c | 6 +++--- 1
> file changed, 3 insertions(+), 3 deletions(-) diff --git
> a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c index
> e303b522efb5..f78fccbc4b93 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; @@ -1791,7 +1791,7 @@ int
> cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in) } /* sanity
> checking */ - if (((offset + len) > skb_in->len) || + if ((offset >
> skb_in->len - len) || (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

I don't mind taking a look at it, but that's beyond unreadable...

Could you please resend using "git send-email" or something else that
works?



Bjørn