[PATCH 1/2] crypto: rng - Override drivers/char/random in FIPS mode

[Jay Wang <wanjay@amazon.com>]

From: Herbert Xu <herbert.xu@redhat.com>

Upstream: RHEL only
Bugzilla: 1984784

This patch overrides the drivers/char/random RNGs with the FIPS
RNG from Crypto API when FIPS mode is enabled.

Cc: stable@vger.kernel.org
Signed-off-by: Herbert Xu <herbert.xu@redhat.com>
(cherry picked from commit 37e0042aaf43d4494bcbea2113605366d0fe6187)
Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>
[6.12: Resolve minor merge conflicts]
Signed-off-by: Elena Avila <ellavila@amazon.com>
---
 crypto/rng.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/crypto/rng.c b/crypto/rng.c
index 9d8804e46422..cdba806846e2 100644
--- a/crypto/rng.c
+++ b/crypto/rng.c
@@ -12,11 +12,14 @@
 #include <linux/atomic.h>
 #include <linux/cryptouser.h>
 #include <linux/err.h>
+#include <linux/fips.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/random.h>
 #include <linux/seq_file.h>
+#include <linux/sched.h>
+#include <linux/sched/signal.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <net/netlink.h>
@@ -217,5 +220,73 @@ void crypto_unregister_rngs(struct rng_alg *algs, int count)
 }
 EXPORT_SYMBOL_GPL(crypto_unregister_rngs);
 
+static ssize_t crypto_devrandom_read(void __user *buf, size_t buflen)
+{
+	u8 tmp[256];
+	ssize_t ret;
+
+	if (!buflen)
+		return 0;
+
+	ret = crypto_get_default_rng();
+	if (ret)
+		return ret;
+
+	for (;;) {
+		int err;
+		int i;
+
+		i = min_t(int, buflen, sizeof(tmp));
+		err = crypto_rng_get_bytes(crypto_default_rng, tmp, i);
+		if (err) {
+			ret = err;
+			break;
+		}
+
+		if (copy_to_user(buf, tmp, i)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		buflen -= i;
+		buf += i;
+		ret += i;
+
+		if (!buflen)
+			break;
+
+		if (need_resched()) {
+			if (signal_pending(current))
+				break;
+			schedule();
+		}
+	}
+
+	crypto_put_default_rng();
+	memzero_explicit(tmp, sizeof(tmp));
+
+	return ret;
+}
+
+static const struct random_extrng crypto_devrandom_rng = {
+	.extrng_read = crypto_devrandom_read,
+	.owner = THIS_MODULE,
+};
+
+static int __init crypto_rng_init(void)
+{
+	if (fips_enabled)
+		random_register_extrng(&crypto_devrandom_rng);
+	return 0;
+}
+
+static void __exit crypto_rng_exit(void)
+{
+	random_unregister_extrng();
+}
+
+late_initcall(crypto_rng_init);
+module_exit(crypto_rng_exit);
+
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("Random Number Generator");
-- 
2.47.1