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Re: [PATCH v3] getrandom system call wrapper [BZ #17252]


On 09/12/2016 09:25 AM, Florian Weimer wrote:
On 09/09/2016 05:23 PM, Torvald Riegel wrote:
On Fri, 2016-09-09 at 16:28 +0200, Florian Weimer wrote:
On 09/09/2016 04:21 PM, Torvald Riegel wrote:
On Thu, 2016-09-08 at 13:44 +0200, Florian Weimer wrote:
I have made the system call wrapper a cancellation point.  (If we
implement the simpler getentropy interface, it would not be a
cancellation point.)

Why did you do that?

I have to, because it can block indefinitely.

That doesn't mean you have to make the default function a cancellation
point.  There are many POSIX functions which can block indefinitely and
which are not required to be cancellation points (eg, rwlocks only *may*
be cancellation points).

Can the system call really block indefinitely, or only for a long time
and (ie, will return eventually)?

Yes, if the system enters a deadlock condition where the waiting for
randomness prevents it from accumulating additional randomness.

This is what happens here:

  <https://bugzilla.redhat.com/show_bug.cgi?id=1383060>

systemd will eventually kill the blocked process and the boot continues, but all network services will be missing.

Florian


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