linux-kernel - [PATCH 2/7] random: print a warning for the first ten uninitialized random users

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Message-Id: <1465832919-11316-3-git-send-email-tytso@mit.edu>
Date:	Mon, 13 Jun 2016 11:48:34 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>
Cc:	linux-crypto@...r.kernel.org, smueller@...onox.de,
	herbert@...dor.apana.org.au, andi@...stfloor.org,
	sandyinchina@...il.com, jsd@...n.com, hpa@...or.com,
	Theodore Ts'o <tytso@....edu>, stable@...nel.org
Subject: [PATCH 2/7] random: print a warning for the first ten uninitialized random users

Since systemd is consistently using /dev/urandom before it is
initialized, we can't see the other potentially dangerous users of
/dev/urandom immediately after boot.  So print the first ten such
complaints instead.

Cc: stable@...nel.org
Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 drivers/char/random.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 4e2627a..74596d3 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1458,12 +1458,16 @@ random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 static ssize_t
 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 {
+	static int maxwarn = 10;
 	int ret;
 
-	if (unlikely(nonblocking_pool.initialized == 0))
-		printk_once(KERN_NOTICE "random: %s urandom read "
-			    "with %d bits of entropy available\n",
-			    current->comm, nonblocking_pool.entropy_total);
+	if (unlikely(nonblocking_pool.initialized == 0) &&
+	    maxwarn > 0) {
+		maxwarn--;
+		printk(KERN_NOTICE "random: %s: uninitialized urandom read "
+		       "(%d bytes read, %d bits of entropy available)\n",
+		       current->comm, nbytes, nonblocking_pool.entropy_total);
+	}
 
 	nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));
 	ret = extract_entropy_user(&nonblocking_pool, buf, nbytes);
-- 
2.5.0