From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from guitar.tcltek.co.il ([192.115.133.116] helo=sivan.tkos.co.il) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1V7jkz-0000eB-Lq for barebox@lists.infradead.org; Fri, 09 Aug 2013 10:17:20 +0000 Date: Fri, 9 Aug 2013 13:16:49 +0300 From: Baruch Siach Message-ID: <20130809101649.GA3703@tarshish> References: <20130809073237.GA26614@pengutronix.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20130809073237.GA26614@pengutronix.de> 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: Sascha Hauer Cc: barebox@lists.infradead.org Hi Sascha, On Fri, Aug 09, 2013 at 09:32:37AM +0200, Sascha Hauer wrote: > 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; You're right, of course. I was just blindly copying the kernel that has this in ip_rcv(): if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl))) goto csum_error; But I still don't understand the logic here. baruch -- http://baruch.siach.name/blog/ ~. .~ Tk Open Systems =}------------------------------------------------ooO--U--Ooo------------{= - baruch@tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il - _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox