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@in.ibm.com> --- 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.
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,
-- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org