From: Dave Taht <dave.taht@gmail.com>
To: cake@lists.bufferbloat.net,
"codel@lists.bufferbloat.net" <codel@lists.bufferbloat.net>
Subject: [Cake] [RFC PATCH] Don't give malicious CE senders a free ride
Date: Wed, 5 Oct 2016 21:28:28 -0700 [thread overview]
Message-ID: <CAA93jw79ahtp_RiA1AzY_J3JEacAG9Qpt8hBZjSynC8jpX3iUQ@mail.gmail.com> (raw)
After doing myself in with BBR not respecting CE marks, I'm now thinking
that perhaps the right thing for red/fq_codel/cake/pie/etc to do is actually
*drop* stuff that it sees that is already CE marked, when it too wants
to mark, instead of giving it a free ride.
It's an unfriendly world out there.
Not happy with the name of the function... and to me - it looks like
the existing call sites for IP_ECN_set_ce would actually be saner if
they always returned 0 instead of !ecn.
diff --git a/include/net/inet_ecn.h b/include/net/inet_ecn.h
index dce2d58..3742d84 100644
--- a/include/net/inet_ecn.h
+++ b/include/net/inet_ecn.h
@@ -71,6 +71,36 @@ static inline void INET_ECN_dontxmit(struct sock *sk)
(label) |= htonl(INET_ECN_ECT_0 << 20); \
} while (0)
+/* When CE is already asserted, sometimes it is saner to drop the packet
+ in order to not give malicious CE senders as much of a free ride. */
+
+static inline int IP_ECN_safe_set_ce(struct iphdr *iph)
+{
+ u32 check = (__force u32)iph->check;
+ u32 ecn = (iph->tos + 1) & INET_ECN_MASK;
+
+ /*
+ * After the last operation we have (in binary):
+ * INET_ECN_NOT_ECT => 01
+ * INET_ECN_ECT_1 => 10
+ * INET_ECN_ECT_0 => 11
+ * INET_ECN_CE => 00
+ */
+ if (!(ecn & 2))
+ return 0;
+
+ /*
+ * The following gives us:
+ * INET_ECN_ECT_1 => check += htons(0xFFFD)
+ * INET_ECN_ECT_0 => check += htons(0xFFFE)
+ */
+ check += (__force u16)htons(0xFFFB) + (__force u16)htons(ecn);
+
+ iph->check = (__force __sum16)(check + (check>=0xFFFF));
+ iph->tos |= INET_ECN_CE;
+ return 1;
+}
+
--
Dave Täht
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org
next reply other threads:[~2016-10-06 4:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-06 4:28 Dave Taht [this message]
2016-10-06 8:18 ` Jonathan Morton
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