linux-kernel - Re: [PATCH v2 4/4] ozwpan: unchecked signed subtraction leads to DoS

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Message-ID: <20150526140654.GI11588@mwanda>
Date:	Tue, 26 May 2015 17:06:55 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	"Jason A. Donenfeld" <Jason@...c4.com>
Cc:	oss-security <oss-security@...ts.openwall.com>,
	linux-kernel@...r.kernel.org,
	Shigekatsu Tateno <shigekatsu.tateno@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org
Subject: Re: [PATCH v2 4/4] ozwpan: unchecked signed subtraction leads to DoS

On Tue, May 26, 2015 at 02:17:49PM +0200, Jason A. Donenfeld wrote:
> diff --git a/drivers/staging/ozwpan/ozusbsvc1.c b/drivers/staging/ozwpan/ozusbsvc1.c
> index 8552053..1bde6aa 100644
> --- a/drivers/staging/ozwpan/ozusbsvc1.c
> +++ b/drivers/staging/ozwpan/ozusbsvc1.c
> @@ -326,11 +326,13 @@ static void oz_usb_handle_ep_data(struct oz_usb_ctx *usb_ctx,
>  			struct oz_multiple_fixed *body =
>  				(struct oz_multiple_fixed *)data_hdr;
>  			u8 *data = body->data;
> -			int n;
> +			unsigned int n;
>  			if (!body->unit_size)
>  				break;
>  			n = (len - sizeof(struct oz_multiple_fixed)+1)
>  				/ body->unit_size;
> +			if (n > len / body->unit_size)
> +				break;

You sure do like wrapping to a high value and testing the result for
wrapping instead of validating before doing the subtraction...

regards,
dan carpenter

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