[PATCH 4.9 055/264] random: add GRND_INSECURE to return best-effort non-cryptographic bytes

Greg Kroah-Hartman
2022-06-23T17:00:42Z

From: Andy Lutomirski <luto@kernel.org>

commit 75551dbf112c992bc6c99a972990b3f272247e23 upstream.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/d5473b56cf1fa900ca4bd2b3fc1e5b8874399919.1577088521.git.luto@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 11 +++++++++--
include/uapi/linux/random.h | 2 ++
2 files changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2187,7 +2187,14 @@ SYSCALL_DEFINE3(getrandom, char __user *
{
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)
@@ -2196,7 +2203,7 @@ SYSCALL_DEFINE3(getrandom, char __user *
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();
--- a/include/uapi/linux/random.h
+++ b/include/uapi/linux/random.h
@@ -48,8 +48,10 @@ 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 */