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From: Michal Kubecek <mkubecek@suse.cz>
To: netdev <netdev@vger.kernel.org>
Cc: Timothy Winters <twinters@iol.unh.edu>,
	Eric Dumazet <edumazet@google.com>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Florian Westphal <fw@strlen.de>,
	Tom Herbert <tom@herbertland.com>,
	David Miller <davem@davemloft.net>,
	Peter Oskolkov <posk@google.com>
Subject: Re: [PATCH v3 23/30] ipv6: defrag: drop non-last frags smaller than min mtu
Date: Fri, 11 Jan 2019 15:21:25 +0100	[thread overview]
Message-ID: <6909509.AEfQCu2WVp@alaris> (raw)
In-Reply-To: <CAOSSMjUODMbBuW=GgwcEt6avKoyYD5A9CzdBtE6NR6dz4pnD6w@mail.gmail.com>

On Friday, 11 January 2019 14:26 Timothy Winters wrote:
> Hi Eric,
> 
> So I understand correctly the attack that you are trying to prevent is
> many small fragments from different IPs?
> 
> The 6MAN working group has had some discussion about this topic, if
> you want read some IPv6 networking prospectives.
> 
> https://mailarchive.ietf.org/arch/browse/ipv6/?gbt=1&index=zsYUwQTt0mA
> dXdk9MN4dP-uiiag

I haven't read all mails in that discussion but most seem to be missing 
the point. The problem is not memory consumption, we have a (runtime 
configurable) limit for that. The problem is that by sending many small 
(8 bytes) fragments of a large (up to 64 KB) packet but never finishing 
it, an attacker can force receiving host into using quite a lot of CPU 
time just by looking up the fragment queue of the partially reassembled 
packet.

Currently, IPv6 reassembly uses a simple linear list which is fine with 
1280 byte long fragments (up to ~50 of them) but not with 8 byte long 
ones (there could be as many as ~8000). The IPv4 reassembly code (where 
we cannot assume minimal size of non-last fragment) switched to rbtree 
(with logarithmic lookup time) exactly for this reason.

> What about lowering the value of accepted fragments?  to something
> like 1280/2?

That would be probably sufficient to mitigate the DoS attacks.

Michal Kubecek

  parent reply	other threads:[~2019-01-11 14:21 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-13 14:58 [PATCH v3 00/30] backport of IP fragmentation fixes Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 01/30] inet: frags: change inet_frags_init_net() return value Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 02/30] inet: frags: add a pointer to struct netns_frags Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 03/30] inet: frags: refactor ipfrag_init() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 04/30] inet: frags: Convert timers to use timer_setup() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 05/30] inet: frags: refactor ipv6_frag_init() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 06/30] inet: frags: refactor lowpan_net_frag_init() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 07/30] ipv6: export ip6 fragments sysctl to unprivileged users Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 08/30] rhashtable: add schedule points Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 09/30] inet: frags: use rhashtables for reassembly units Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 10/30] inet: frags: remove some helpers Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 11/30] inet: frags: get rif of inet_frag_evicting() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 12/30] inet: frags: remove inet_frag_maybe_warn_overflow() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 13/30] inet: frags: break the 2GB limit for frags storage Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 14/30] inet: frags: do not clone skb in ip_expire() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 15/30] ipv6: frags: rewrite ip6_expire_frag_queue() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 16/30] rhashtable: reorganize struct rhashtable layout Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 17/30] inet: frags: reorganize struct netns_frags Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 18/30] inet: frags: get rid of ipfrag_skb_cb/FRAG_CB Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 19/30] inet: frags: fix ip6frag_low_thresh boundary Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 20/30] ip: discard IPv4 datagrams with overlapping segments Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 21/30] net: speed up skb_rbtree_purge() Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 22/30] net: modify skb_rbtree_purge to return the truesize of all purged skbs Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 23/30] ipv6: defrag: drop non-last frags smaller than min mtu Stephen Hemminger
2019-01-10 19:30   ` Tom Herbert
2019-01-10 22:22     ` Florian Westphal
2019-01-11 10:57       ` Eric Dumazet
2019-01-11 12:21         ` Michal Kubecek
2019-01-11 12:27           ` Eric Dumazet
2019-01-11 12:52             ` Michal Kubecek
2019-01-11 13:07               ` Eric Dumazet
     [not found]                 ` <CAOSSMjUODMbBuW=GgwcEt6avKoyYD5A9CzdBtE6NR6dz4pnD6w@mail.gmail.com>
2019-01-11 14:09                   ` Eric Dumazet
2019-01-11 14:21                   ` Michal Kubecek [this message]
     [not found]                     ` <CAOSSMjVMVWxzkT5M2LHgf0+GPHdaWHV01a6mBqbGRVXOaQ04PQ@mail.gmail.com>
2019-01-11 17:09                       ` Peter Oskolkov
2019-01-11 18:10                         ` Michal Kubecek
2019-01-12  3:21                           ` Tom Herbert
2018-09-13 14:58 ` [PATCH v3 24/30] net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 25/30] net: add rb_to_skb() and other rb tree helpers Stephen Hemminger
2018-09-13 14:58 ` [PATCH v3 26/30] net: sk_buff rbnode reorg Stephen Hemminger
2018-10-18 16:01   ` Christoph Paasch
2018-09-13 14:58 ` [PATCH v3 27/30] ipv4: frags: precedence bug in ip_expire() Stephen Hemminger
2018-09-13 14:59 ` [PATCH v3 28/30] ip: add helpers to process in-order fragments faster Stephen Hemminger
2018-09-13 14:59 ` [PATCH v3 29/30] ip: process in-order fragments efficiently Stephen Hemminger
2018-09-13 14:59 ` [PATCH v3 30/30] ip: frags: fix crash in ip_do_fragment() Stephen Hemminger
2018-09-17 12:47 ` [PATCH v3 00/30] backport of IP fragmentation fixes Greg KH

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