From: Kurt Roeckx <kurt@roeckx.be>
To: "Theodore Y. Ts'o" <tytso@mit.edu>,
"Sebastian Andrzej Siewior" <sebastian@breakpoint.cc>,
912087@bugs.debian.org,
"Package Development List for OpenSSL packages."
<pkg-openssl-devel@alioth-lists.debian.net>,
linux-kernel@vger.kernel.org,
"Bernhard Übelacker" <bernhardu@mailbox.org>,
pkg-systemd-maintainers@lists.alioth.debian.org,
debian-ssh@lists.debian.org, 912087-submitter@bugs.debian.org
Subject: Re: Bug#912087: openssh-server: Slow startup after the upgrade to 7.9p1
Date: Tue, 30 Oct 2018 19:37:23 +0100 [thread overview]
Message-ID: <20181030183723.GI10011@roeckx.be> (raw)
In-Reply-To: <20181030141544.GE15839@thunk.org>
On Tue, Oct 30, 2018 at 10:15:44AM -0400, Theodore Y. Ts'o wrote:
> On Tue, Oct 30, 2018 at 01:18:08AM +0100, Sebastian Andrzej Siewior wrote:
> > Using ioctl(/dev/urandom, RNDADDENTROPY, ) instead writting to
> > /dev/urandom would do the trick. Or using RNDADDTOENTCNT to increment
> > the entropy count after it was written. Those two are documented in
> > random(4). Or RNDRESEEDCRNG could be used to force crng to be reseeded.
> > It does also the job, too.
> >
> > Ted, is there any best practise what to do with the seed which as
> > extrected from /dev/urandom on system shutdown? Using RNDADDTOENTCNT to
> > speed up init or just write to back to urandom and issue RNDRESEEDCRNG?
>
> The reason why writing to /dev/[u]random via something like:
>
> cat /var/lib/random/seed > /dev/random
>
> Dosn't bump the the entropy counter is because it's possible that an
> attacker could read /var/lib/random/seed. Even if the seed file is
> refreshed on shutdown, (a) the attacker could have read the file while
> the system is down, or (b) the system could have crashed so the seed
> file was not refreshed and the attacker could have read the file
> before the crash.
So are you saying that the /var/lib/random/seed is untrusted, and
should never be used, and we should always wait for fresh entropy?
Anyway, I think if an attacker somehow has access to that file,
you have much more serious problems.
Kurt
next prev parent reply other threads:[~2018-10-30 18:47 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20181029223334.GH10011@roeckx.be>
2018-10-30 0:18 ` Bug#912087: openssh-server: Slow startup after the upgrade to 7.9p1 Sebastian Andrzej Siewior
2018-10-30 14:15 ` Theodore Y. Ts'o
2018-10-30 18:37 ` Kurt Roeckx [this message]
2018-10-30 20:51 ` Theodore Y. Ts'o
2018-10-31 11:21 ` Sebastian Andrzej Siewior
2018-10-31 22:41 ` Theodore Y. Ts'o
2018-11-01 22:18 ` Sebastian Andrzej Siewior
2018-11-01 23:50 ` Theodore Y. Ts'o
2018-11-02 0:24 ` Kurt Roeckx
2018-11-02 2:13 ` Theodore Y. Ts'o
2018-11-04 0:18 ` Sebastian Andrzej Siewior
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