On 11/18/2013 08:45 PM, Eric Blake wrote:
> On 11/18/2013 06:28 AM, Pradipta Kr. Banerjee wrote:
>> Creating a qemu VM with /dev/hwrng as backed RNG device throws the
>> following error - "Could not open '/dev/hwrng': Operation not permitted"
>> This patch fixes the issue
>>
>> Signed-off-by: Pradipta Kr. Banerjee <bpradip@xxxxxxxxxx>
>> ---
>> src/qemu/qemu_cgroup.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> This is probably not the right fix. This says that we are making the
> random device to all possible guests, and that a compromised guest can
> then open() the device and starve it of entropy to the detriment of
> other guests. I think the _real_ fix is to quit exposing /dev/random by
> default (/dev/urandom may be okay), and to instead teach the code for
> RNG devices to add an ACL change for either random device (/dev/random
> or /dev/hwrng) only for the guests that actually use RNG backed by a
> hardware device. That way, guests not using an RNG device cannot starve
> entropy from guests that depend on it.
Right..Thanks for the suggestion Eric.
>
>>
>> diff --git a/src/qemu/qemu_cgroup.c b/src/qemu/qemu_cgroup.c
>> index ace7e35..d9ebb30 100644
>> --- a/src/qemu/qemu_cgroup.c
>> +++ b/src/qemu/qemu_cgroup.c
>> @@ -39,7 +39,7 @@
>>
>> static const char *const defaultDeviceACL[] = {
>> "/dev/null", "/dev/full", "/dev/zero",
>> - "/dev/random", "/dev/urandom",
>> + "/dev/random", "/dev/urandom", "/dev/hwrng",
>> "/dev/ptmx", "/dev/kvm", "/dev/kqemu",
>> "/dev/rtc", "/dev/hpet", "/dev/vfio/vfio",
>> NULL,
>>
>
--
Regards,
Pradipta
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