backends/rng-random.c | 2 +- qemu-options.hx | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
When QEMU exposes a VirtIO-RNG device to the guest, that device needs a
source of entropy, and that source needs to be "non-blocking", like
`/dev/urandom`. However, currently QEMU defaults to the problematic
`/dev/random`, which is "blocking" (as in, it waits until sufficient
entropy is available).
So change the entropy source to the recommended `/dev/urandom`.
Related discussion in these[1][2] past threads.
[1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html
-- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?"
[2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html
-- "[RFC] Virtio RNG: Consider changing the default entropy source to
/dev/urandom"
Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
---
backends/rng-random.c | 2 +-
qemu-options.hx | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/backends/rng-random.c b/backends/rng-random.c
index e2a49b0571..eff36ef140 100644
--- a/backends/rng-random.c
+++ b/backends/rng-random.c
@@ -112,7 +112,7 @@ static void rng_random_init(Object *obj)
rng_random_set_filename,
NULL);
- s->filename = g_strdup("/dev/random");
+ s->filename = g_strdup("/dev/urandom");
s->fd = -1;
}
diff --git a/qemu-options.hx b/qemu-options.hx
index 51802cbb26..a525609149 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4276,7 +4276,7 @@ Creates a random number generator backend which obtains entropy from
a device on the host. The @option{id} parameter is a unique ID that
will be used to reference this entropy backend from the @option{virtio-rng}
device. The @option{filename} parameter specifies which file to obtain
-entropy from and if omitted defaults to @option{/dev/random}.
+entropy from and if omitted defaults to @option{/dev/urandom}.
@item -object rng-egd,id=@var{id},chardev=@var{chardevid}
--
2.17.2
On Fri, May 03, 2019 at 05:46:13PM +0200, Kashyap Chamarthy wrote: > When QEMU exposes a VirtIO-RNG device to the guest, that device needs a > source of entropy, and that source needs to be "non-blocking", like > `/dev/urandom`. However, currently QEMU defaults to the problematic > `/dev/random`, which is "blocking" (as in, it waits until sufficient > entropy is available). > > So change the entropy source to the recommended `/dev/urandom`. > > Related discussion in these[1][2] past threads. > > [1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html > -- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?" > [2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html > -- "[RFC] Virtio RNG: Consider changing the default entropy source to > /dev/urandom" > > Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com> > --- > backends/rng-random.c | 2 +- > qemu-options.hx | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Fri, May 03, 2019 at 04:49:05PM +0100, Daniel P. Berrangé wrote: > On Fri, May 03, 2019 at 05:46:13PM +0200, Kashyap Chamarthy wrote: > > When QEMU exposes a VirtIO-RNG device to the guest, that device needs a > > source of entropy, and that source needs to be "non-blocking", like > > `/dev/urandom`. However, currently QEMU defaults to the problematic > > `/dev/random`, which is "blocking" (as in, it waits until sufficient > > entropy is available). > > > > So change the entropy source to the recommended `/dev/urandom`. > > > > Related discussion in these[1][2] past threads. > > > > [1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html > > -- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?" > > [2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html > > -- "[RFC] Virtio RNG: Consider changing the default entropy source to > > /dev/urandom" > > > > Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com> > > --- > > backends/rng-random.c | 2 +- > > qemu-options.hx | 2 +- > > 2 files changed, 2 insertions(+), 2 deletions(-) > > Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> I'm wondering if this needs to be mentioned on a Release Notes wiki somewhere -- because we're changing the default. -- /kashyap
On Fri, May 03, 2019 at 10:47:57PM +0200, Kashyap Chamarthy wrote: > On Fri, May 03, 2019 at 04:49:05PM +0100, Daniel P. Berrangé wrote: > > On Fri, May 03, 2019 at 05:46:13PM +0200, Kashyap Chamarthy wrote: > > > When QEMU exposes a VirtIO-RNG device to the guest, that device needs a > > > source of entropy, and that source needs to be "non-blocking", like > > > `/dev/urandom`. However, currently QEMU defaults to the problematic > > > `/dev/random`, which is "blocking" (as in, it waits until sufficient > > > entropy is available). > > > > > > So change the entropy source to the recommended `/dev/urandom`. > > > > > > Related discussion in these[1][2] past threads. > > > > > > [1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html > > > -- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?" > > > [2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html > > > -- "[RFC] Virtio RNG: Consider changing the default entropy source to > > > /dev/urandom" > > > > > > Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com> > > > --- > > > backends/rng-random.c | 2 +- > > > qemu-options.hx | 2 +- > > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> > > I'm wondering if this needs to be mentioned on a Release Notes wiki > somewhere -- because we're changing the default. Release notes need to get updated when pull requests merge to mention any user relevant changes. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Fri, May 03, 2019 at 05:46:13PM +0200, Kashyap Chamarthy wrote:
> When QEMU exposes a VirtIO-RNG device to the guest, that device needs a
> source of entropy, and that source needs to be "non-blocking", like
> `/dev/urandom`. However, currently QEMU defaults to the problematic
> `/dev/random`, which is "blocking" (as in, it waits until sufficient
> entropy is available).
>
> So change the entropy source to the recommended `/dev/urandom`.
>
> Related discussion in these[1][2] past threads.
>
> [1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html
> -- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?"
> [2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html
> -- "[RFC] Virtio RNG: Consider changing the default entropy source to
> /dev/urandom"
>
> Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
> ---
> backends/rng-random.c | 2 +-
> qemu-options.hx | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/backends/rng-random.c b/backends/rng-random.c
> index e2a49b0571..eff36ef140 100644
> --- a/backends/rng-random.c
> +++ b/backends/rng-random.c
> @@ -112,7 +112,7 @@ static void rng_random_init(Object *obj)
> rng_random_set_filename,
> NULL);
>
> - s->filename = g_strdup("/dev/random");
> + s->filename = g_strdup("/dev/urandom");
> s->fd = -1;
> }
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 51802cbb26..a525609149 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -4276,7 +4276,7 @@ Creates a random number generator backend which obtains entropy from
> a device on the host. The @option{id} parameter is a unique ID that
> will be used to reference this entropy backend from the @option{virtio-rng}
> device. The @option{filename} parameter specifies which file to obtain
> -entropy from and if omitted defaults to @option{/dev/random}.
> +entropy from and if omitted defaults to @option{/dev/urandom}.
>
> @item -object rng-egd,id=@var{id},chardev=@var{chardevid}
I think this is a very sensible change, removing a bit of superstition
about randomness.
Reviewed-by: Richard W.M. Jones <rjones@redhat.com>
Rich.
--
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