netdev - Re: [PATCH net-next-2.6 v2] ipv4: more compliant RFC 3168 support

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Message-ID: <1305573466.2503.12.camel@Joe-Laptop>
Date:	Mon, 16 May 2011 12:17:46 -0700
From:	Joe Perches <joe@...ches.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Stefanos Harhalakis <v13@....gr>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6 v2] ipv4: more compliant RFC 3168 support

On Mon, 2011-05-16 at 20:37 +0200, Eric Dumazet wrote:
> Commit 6623e3b24a5e (ipv4: IP defragmentation must be ECN aware) was an
> attempt to not lose "Congestion Experienced" (CE) indications when
> performing datagram defragmentation.
> Stefanos Harhalakis raised the point that RFC 3168 requirements were not
> completely met by this commit.
> In particular, we MUST detect invalid combinations and eventually drop
> illegal frames.
> Reported-by: Stefanos Harhalakis <v13@....gr>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> ---
> v2 : Use a table instead of a switch()

Just trivia:

bitmasks and hard coded constants can be a bit of a minefield.

> diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
> @@ -77,22 +77,42 @@ struct ipq {
[]
> +/* RFC 3168 support :
> + * We want to check ECN values of all fragments, do detect invalid combinations.
> + * In ipq->ecn, we store the OR value of each ip4_frag_ecn() fragment value.
> + */
> +enum {
> +	IPFRAG_ECN_NOT_ECT	= 0x01, /* one frag had ECN_NOT_ECT */
> +	IPFRAG_ECN_ECT_1	= 0x02, /* one frag had ECN_ECT_1 */
> +	IPFRAG_ECN_ECT_0	= 0x04, /* one frag had ECN_ECT_0 */
> +	IPFRAG_ECN_CE		= 0x08, /* one frag had ECN_CE */

Might be better to have a IPFRAG_ECN_TABLESIZE or some such.

	IPFRAG_ECN_TABLESIZE = 0x10,

> +static const u8 ip4_frag_ecn_table[16] = {

static const u8 ip4_frag_ecn_table[IPFRAG_ECN_TABLESIZE] = {


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