commit 82c1e117cabe36ffe91980fb93e01f92038ad7c4
author Andy Lutomirski <luto@kernel.org> Mon Dec 23 00:20:46 2019 -0800
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> Sat Jun 25 11:45:02 2022 +0200
tree 399fc0ee8566ea678907baad6900c7bef2d74224
parent a7b2d8f6e6e350f3ecbee2cbe7c143726b211a68

random: add GRND_INSECURE to return best-effort non-cryptographic bytes

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

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 7d802fe..284ffd0 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2187,7 +2187,14 @@
 {
 	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 @@
 	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();

include/uapi/linux/random.h

diff --git a/include/uapi/linux/random.h b/include/uapi/linux/random.h
index b455b0d..77c1e73 100644
--- a/include/uapi/linux/random.h
+++ b/include/uapi/linux/random.h
@@ -48,8 +48,10 @@
  *
  * 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 */