linux-kernel - [PATCH 3.16 010/346] random: print a warning for the first ten uninitialized random users

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Message-ID: <lsq.1479082460.635033980@decadent.org.uk>
Date:   Mon, 14 Nov 2016 00:14:20 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 3.16 010/346] random: print a warning for the first ten
 uninitialized random users

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@....edu>

commit 9b4d008787f864f17d008c9c15bbe8a0f7e2fc24 upstream.

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.

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

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1379,12 +1379,16 @@ random_read(struct file *file, char __us
 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 "
+		       "(%zd 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);