netdev - Re: Enable syn cookies by default

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 21 Oct 2009 09:48:18 +0200
From:	Olaf van der Spek <olafvdspek@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Enable syn cookies by default

On Wed, Oct 21, 2009 at 9:25 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Olaf van der Spek a écrit :
>> On Thu, Oct 15, 2009 at 10:59 AM, Olaf van der Spek
>> <olafvdspek@...il.com> wrote:
>>> On Sat, Oct 10, 2009 at 3:01 PM, Olaf van der Spek <olafvdspek@...il.com> wrote:
>>>> Hi,
>>>>
>>>> I'm forwarding Debian feature request #520668.
>>>>
>>>> Could syn cookies be enabled by default?
>>>>
>>>> AFAIK syn cookies only get send when the half-open TCP connection
>>>> queue is full. So stuff like window scaling should work fine in normal
>>>> situations.
>>>>
>>>> Speaking of which:
>>>> When the half-open TCP connection queue is full and syn cookies are
>>>> enabled, you get a message like "kernel: possible SYN flooding on port
>>>> 2710. Sending cookies."
>>>> However when syn cookies are disabled, you don't get any message (in
>>>> kern.log), although connections to your server are timing out.
>>>> Could such a message be added?
>>>> Maybe with a suggestion to increase the size of that queue or to
>>>> enable syn cookies.
>>>>
>>>> Greetings,
>>>>
>>>> Olaf
>>>>
>>>> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=520668
>>>> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=520667
>>>> https://bugs.launchpad.net/ubuntu/+bug/57091
>>>>
>>> Somebody?
>>
>> Anybody?
>
> This is a user selectable setting. What's wrong with /etc/sysctl.conf ?

It requires user action...
Often you notice cookies are disabled only after a service becomes unreachable.
What's wrong with improving defaults?
Don't forget the missing log entries.

Olaf
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html