From: Jason A. Donenfeld <Jason@zx2c4.com>
Date: Wed, 9 Feb 2022 17:42:13 +0000 (+0100)
Subject: random: zero buffer after reading entropy from userspace
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=d2d1ad9430b1e23aa2f82bca561e85868c519383;p=linux.git

random: zero buffer after reading entropy from userspace

commit 7b5164fb1279bf0251371848e40bae646b59b3a8 upstream.

This buffer may contain entropic data that shouldn't stick around longer
than needed, so zero out the temporary buffer at the end of write_pool().

Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 88f55921757f1..6108403564079 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1336,19 +1336,24 @@ static __poll_t random_poll(struct file *file, poll_table *wait)
 static int write_pool(const char __user *ubuf, size_t count)
 {
 	size_t len;
+	int ret = 0;
 	u8 block[BLAKE2S_BLOCK_SIZE];
 
 	while (count) {
 		len = min(count, sizeof(block));
-		if (copy_from_user(block, ubuf, len))
-			return -EFAULT;
+		if (copy_from_user(block, ubuf, len)) {
+			ret = -EFAULT;
+			goto out;
+		}
 		count -= len;
 		ubuf += len;
 		mix_pool_bytes(block, len);
 		cond_resched();
 	}
 
-	return 0;
+out:
+	memzero_explicit(block, sizeof(block));
+	return ret;
 }
 
 static ssize_t random_write(struct file *file, const char __user *buffer,