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[bug#29725] [PATCH 2/2] services: urandom-seed: Try using a HWRNG to see
[bug#29725] [PATCH 2/2] services: urandom-seed: Try using a HWRNG to seed the Linux CRNG at boot.
Mon, 18 Dec 2017 00:30:18 -0500
On Sun, Dec 17, 2017 at 04:31:27PM +0100, Ludovic Courtès wrote:
> Leo Famulari <address@hidden> skribis:
> If we fail to read from /dev/hwrng we may end up writing zeros to
> /dev/urandom (because ‘buf’ is left uninitialized).
Right, the patch I sent wrote the buffer to urandom unconditionally.
It's sloppy when the buffer is uninitialized but does no harm to the
> To address that, perhaps this could be formulated like this:
> (let ((buf (catch 'system-error
> (lambda ()
> (call-with-input-file "/dev/hwrng"
> (lambda (port)
> (get-bytevector-n port 512))))
> (const #f))))
> (when buf
> (call-with-output-file "/dev/urandom"
> (lambda (urandom)
> (put-bytevector urandom buf)))))
Overall I like this better.
I tested it and catching system-error seems to work for the case when
/dev/hwrng exists but there is nothing actually there.
I noticed you used get-bytevector-n instead of get-bytevector-n!. The
documentation says that the former reads "octets" while the latter reads
"bytes" . I guess there is no difference in practice in 2017, right?
> This also removes the need for the ‘file-exists?’ call.
I don't know what creates /dev/hwrng or under what conditions. I didn't
see it in (gnu build linux-boot). Can we rely on it to exist for all the
versions of Linux we support?
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