linux-kernel - [PATCH] random: fix rdrand mix-in

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Message-Id: <20180717135307.3713325-1-arnd@arndb.de>
Date:   Tue, 17 Jul 2018 15:53:00 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "Theodore Ts'o" <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jann Horn <jannh@...gle.com>, "Tobin C. Harding" <me@...in.cc>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] random: fix rdrand mix-in

The newly added arch_get_random_int() call was done incorrectly,
using the output only if rdrand hardware was /not/ available. The
compiler points out that the data is uninitialized in this case:

drivers/char/random.c: In function 'write_pool.constprop':
drivers/char/random.c:1912:11: error: 't' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This fixes the condition so we only use that data when it was
valid.

Fixes: 349ddb707fb7 ("random: mix rdrand with entropy sent in from userspace")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/char/random.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 283fe390e878..71660aef8c8c 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1907,7 +1907,7 @@ write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
 			return -EFAULT;
 
 		for (b = bytes ; b > 0 ; b -= sizeof(__u32), i++) {
-			if (arch_get_random_int(&t))
+			if (!arch_get_random_int(&t))
 				continue;
 			buf[i] ^= t;
 		}
-- 
2.9.0