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From: "fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug libc/29437] arc4random is too slow
Date: Mon, 08 Aug 2022 12:43:36 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29437

--- Comment #12 from Florian Weimer <fweimer at redhat dot com> ---
(In reply to Adhemerval Zanella from comment #9)
> (In reply to Florian Weimer from comment #7)
> > (In reply to Adhemerval Zanella from comment #6)
> > > For example, when a virtual machine is forked, restored, or duplicate=
d, it's
> > > imperative that the RNG doesn't generate the same outputs. For this r=
eason,
> > > there's a small protocol between hypervisors and the kernel that indi=
cates
> > > this has happened, alongside some ID, which the RNG uses to reseed
> > > immediately, so as not to return the same numbers.
> >=20
> > Except that this doesn't work because if the suspend/resume happens a l=
ittle
> > bit later, the unprotected application buffer to which the random data =
has
> > been written is restore multiple times. So clearly the actual rules aro=
und
> > this are different and much more complicated.
>=20
> I am not following, which buffer are you referring? The kernel one
> application will be poll with arc4random/getrandom or the possible one
> maintained by application itself with a previous arc4random call?

If suspended right after arc4random () returms, this

printf ("%u\n", (unsigned int) arc4random ());

will print the same number after each resumption.

--=20
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