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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Jann Horn <jannh@google.com>,
        Eric Biggers <ebiggers@google.com>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>
Subject: [PATCH 5.17 021/111] random: zero buffer after reading entropy from userspace
Date:   Fri, 27 May 2022 10:48:53 +0200
Message-Id: <20220527084822.362277500@linuxfoundation.org>
In-Reply-To: <20220527084819.133490171@linuxfoundation.org>
References: <20220527084819.133490171@linuxfoundation.org>
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From: "Jason A. Donenfeld" <Jason@zx2c4.com>

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>
---
 drivers/char/random.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1336,19 +1336,24 @@ static __poll_t random_poll(struct file
 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,