From: Sascha Hauer <s.hauer@pengutronix.de>
To: Baruch Siach <baruch@tkos.co.il>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH] net: fix checksum verification
Date: Fri, 9 Aug 2013 09:32:37 +0200 [thread overview]
Message-ID: <20130809073237.GA26614@pengutronix.de> (raw)
In-Reply-To: <ce9d0dc069aa93694635e8bd5ac2fbd94bd2fa24.1376020752.git.baruch@tkos.co.il>
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 <baruch@tkos.co.il>
> ---
>
> 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
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next prev parent reply other threads:[~2013-08-09 7:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-09 4:01 Baruch Siach
2013-08-09 7:32 ` Sascha Hauer [this message]
2013-08-09 8:50 ` Uwe Kleine-König
2013-08-09 8:57 ` Sascha Hauer
2013-08-09 10:16 ` Baruch Siach
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