From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:6f8:1178:4:290:27ff:fe1d:cc33]) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1V7hBz-0004oz-Fi for barebox@lists.infradead.org; Fri, 09 Aug 2013 07:33:00 +0000 Date: Fri, 9 Aug 2013 09:32:37 +0200 From: Sascha Hauer Message-ID: <20130809073237.GA26614@pengutronix.de> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH] net: fix checksum verification To: Baruch Siach Cc: barebox@lists.infradead.org On Fri, Aug 09, 2013 at 07:01:24AM +0300, Baruch Siach wrote: > Checksum verification on data including its own checksum (as is the case with > IP headers) should give zero. Current code works well for the correct checksum > case, but fails to identify (most) errors. > > Signed-off-by: Baruch Siach > --- > > Untested. From code inspection only. > > net/net.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/net.c b/net/net.c > index 0bd9084..bd7a578 100644 > --- a/net/net.c > +++ b/net/net.c > @@ -41,7 +41,7 @@ static unsigned int net_ip_id; > > int net_checksum_ok(unsigned char *ptr, int len) > { > - return net_checksum(ptr, len) + 1; > + return net_checksum(ptr, len) == 0; D'oh. There's a bug indeed. For a good packet net_checksum returns 0xffff (all ones in an u16). So the check should be: return net_checksum(ptr, len) == 0xffff; U-Boot has this instead: return !((net_checksum(ptr, len) + 1) & 0xfffe); >From what I see both above should be equivalent so I wonder why U-Boot has such a complicated code here. Some compiler optimization or is this something I don't see? Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox