[PATCH v2 2/7] random: Add GRND_INSECURE to return best-effort non-cryptographic bytes

[Andy Lutomirski]

Signed-off-by: Andy Lutomirski <l...@kernel.org>
---
 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