From: Eric Dumazet <edumazet@google.com>
To: Willy Tarreau <w@1wt.eu>
Cc: netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
David Miller <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
Amit Klein <aksecurity@gmail.com>
Subject: Re: [PATCH net-next] ipv6: use prandom_u32() for ID generation
Date: Mon, 31 May 2021 21:27:13 +0200 [thread overview]
Message-ID: <CANn89iJsTNoWNZ1rvkQB8a6ROTvh_85P+TuffS0_w5CpJW+4bg@mail.gmail.com> (raw)
In-Reply-To: <20210529110746.6796-1-w@1wt.eu>
On Sat, May 29, 2021 at 1:08 PM Willy Tarreau <w@1wt.eu> wrote:
>
> This is a complement to commit aa6dd211e4b1 ("inet: use bigger hash
> table for IP ID generation"), but focusing on some specific aspects
> of IPv6.
>
> Contary to IPv4, IPv6 only uses packet IDs with fragments, and with a
> minimum MTU of 1280, it's much less easy to force a remote peer to
> produce many fragments to explore its ID sequence. In addition packet
> IDs are 32-bit in IPv6, which further complicates their analysis. On
> the other hand, it is often easier to choose among plenty of possible
> source addresses and partially work around the bigger hash table the
> commit above permits, which leaves IPv6 partially exposed to some
> possibilities of remote analysis at the risk of weakening some
> protocols like DNS if some IDs can be predicted with a good enough
> probability.
>
> Given the wide range of permitted IDs, the risk of collision is extremely
> low so there's no need to rely on the positive increment algorithm that
> is shared with the IPv4 code via ip_idents_reserve(). We have a fast
> PRNG, so let's simply call prandom_u32() and be done with it.
>
> Performance measurements at 10 Gbps couldn't show any difference with
> the previous code, even when using a single core, because due to the
> large fragments, we're limited to only ~930 kpps at 10 Gbps and the cost
> of the random generation is completely offset by other operations and by
> the network transfer time. In addition, this change removes the need to
> update a shared entry in the idents table so it may even end up being
> slightly faster on large scale systems where this matters.
>
> The risk of at least one collision here is about 1/80 million among
> 10 IDs, 1/850k among 100 IDs, and still only 1/8.5k among 1000 IDs,
> which remains very low compared to IPv4 where all IDs are reused
> every 4 to 80ms on a 10 Gbps flow depending on packet sizes.
>
> Reported-by: Amit Klein <aksecurity@gmail.com>
> Cc: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Willy Tarreau <w@1wt.eu>
Reviewed-by: Eric Dumazet <edumazet@google.com>
> ---
> net/ipv6/output_core.c | 28 +++++-----------------------
> 1 file changed, 5 insertions(+), 23 deletions(-)
>
> diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
> index af36acc1a644..2880dc7d9a49 100644
> --- a/net/ipv6/output_core.c
> +++ b/net/ipv6/output_core.c
> @@ -15,29 +15,11 @@ static u32 __ipv6_select_ident(struct net *net,
> const struct in6_addr *dst,
> const struct in6_addr *src)
> {
> - const struct {
> - struct in6_addr dst;
> - struct in6_addr src;
> - } __aligned(SIPHASH_ALIGNMENT) combined = {
> - .dst = *dst,
> - .src = *src,
> - };
> - u32 hash, id;
> -
> - /* Note the following code is not safe, but this is okay. */
> - if (unlikely(siphash_key_is_zero(&net->ipv4.ip_id_key)))
> - get_random_bytes(&net->ipv4.ip_id_key,
> - sizeof(net->ipv4.ip_id_key));
> -
> - hash = siphash(&combined, sizeof(combined), &net->ipv4.ip_id_key);
> -
> - /* Treat id of 0 as unset and if we get 0 back from ip_idents_reserve,
> - * set the hight order instead thus minimizing possible future
> - * collisions.
> - */
> - id = ip_idents_reserve(hash, 1);
> - if (unlikely(!id))
> - id = 1 << 31;
> + u32 id;
> +
> + do {
> + id = prandom_u32();
> + } while (!id);
>
> return id;
> }
> --
> 2.17.5
>
next prev parent reply other threads:[~2021-05-31 19:27 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-29 11:07 [PATCH net-next] ipv6: use prandom_u32() for ID generation Willy Tarreau
2021-05-31 10:41 ` David Laight
2021-05-31 11:19 ` Willy Tarreau
2021-05-31 19:27 ` Eric Dumazet [this message]
2021-06-01 5:20 ` patchwork-bot+netdevbpf
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CANn89iJsTNoWNZ1rvkQB8a6ROTvh_85P+TuffS0_w5CpJW+4bg@mail.gmail.com \
--to=edumazet@google.com \
--cc=aksecurity@gmail.com \
--cc=davem@davemloft.net \
--cc=kuba@kernel.org \
--cc=kuznet@ms2.inr.ac.ru \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=w@1wt.eu \
--cc=yoshfuji@linux-ipv6.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).