[PATCH 2/7] random: Add GRND_INSECURE to return best-effort non-cryptographic bytes

Andy Lutomirski
2019-08-30T01:11:52Z

drivers/char/random.c | 11 +++++++++--
include/uapi/linux/random.h | 2 ++
2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index d152612e08fc..acabb870f222 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2122,7 +2122,14 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
{
int ret;

- if (flags & ~(GRND_NONBLOCK|GRND_RANDOM))
+ if (flags & ~(GRND_NONBLOCK|GRND_RANDOM|GRND_INSECURE))
+ return -EINVAL;
+
+ /*
+ * Requesting insecure and blocking randomness at the same time makes
+ * no sense.
+ */
+ if ((flags & (GRND_INSECURE|GRND_RANDOM)) == (GRND_INSECURE|GRND_RANDOM))
return -EINVAL;

if (count > INT_MAX)
@@ -2131,7 +2138,7 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
if (flags & GRND_RANDOM)
return _random_read(flags & GRND_NONBLOCK, buf, count);

- if (!crng_ready()) {
+ if (!(flags & GRND_INSECURE) && !crng_ready()) {
if (flags & GRND_NONBLOCK)
return -EAGAIN;
ret = wait_for_random_bytes();
diff --git a/include/uapi/linux/random.h b/include/uapi/linux/random.h
index 26ee91300e3e..c092d20088d3 100644
--- a/include/uapi/linux/random.h
+++ b/include/uapi/linux/random.h
@@ -49,8 +49,10 @@ struct rand_pool_info {
*
* GRND_NONBLOCK Don't block and return EAGAIN instead
* GRND_RANDOM Use the /dev/random pool instead of /dev/urandom
+ * GRND_INSECURE Return non-cryptographic random bytes
*/
#define GRND_NONBLOCK 0x0001
#define GRND_RANDOM 0x0002
+#define GRND_INSECURE 0x0004

#endif /* _UAPI_LINUX_RANDOM_H */
--
2.21.0