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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, Theodore Tso <tytso@mit.edu>
Subject: [PATCH 4.16 008/113] random: rate limit unseeded randomness warnings
Date:   Mon, 30 Apr 2018 12:23:39 -0700
Message-Id: <20180430184015.422520343@linuxfoundation.org>
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4.16-stable review patch.  If anyone has any objections, please let me know.

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

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

commit 4e00b339e264802851aff8e73cde7d24b57b18ce upstream.

On systems without sufficient boot randomness, no point spamming dmesg.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/char/random.c |   39 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 34 insertions(+), 5 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -261,6 +261,7 @@
 #include <linux/ptrace.h>
 #include <linux/workqueue.h>
 #include <linux/irq.h>
+#include <linux/ratelimit.h>
 #include <linux/syscalls.h>
 #include <linux/completion.h>
 #include <linux/uuid.h>
@@ -438,6 +439,16 @@ static void _crng_backtrack_protect(stru
 static void process_random_ready_list(void);
 static void _get_random_bytes(void *buf, int nbytes);
 
+static struct ratelimit_state unseeded_warning =
+	RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3);
+static struct ratelimit_state urandom_warning =
+	RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
+
+static int ratelimit_disable __read_mostly;
+
+module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
+MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
+
 /**********************************************************************
  *
  * OS independent entropy store.   Here are the functions which handle
@@ -931,6 +942,18 @@ static void crng_reseed(struct crng_stat
 		process_random_ready_list();
 		wake_up_interruptible(&crng_init_wait);
 		pr_notice("random: crng init done\n");
+		if (unseeded_warning.missed) {
+			pr_notice("random: %d get_random_xx warning(s) missed "
+				  "due to ratelimiting\n",
+				  unseeded_warning.missed);
+			unseeded_warning.missed = 0;
+		}
+		if (urandom_warning.missed) {
+			pr_notice("random: %d urandom warning(s) missed "
+				  "due to ratelimiting\n",
+				  urandom_warning.missed);
+			urandom_warning.missed = 0;
+		}
 	}
 }
 
@@ -1574,8 +1597,9 @@ static void _warn_unseeded_randomness(co
 #ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM
 	print_once = true;
 #endif
-	pr_notice("random: %s called from %pS with crng_init=%d\n",
-		  func_name, caller, crng_init);
+	if (__ratelimit(&unseeded_warning))
+		pr_notice("random: %s called from %pS with crng_init=%d\n",
+			  func_name, caller, crng_init);
 }
 
 /*
@@ -1769,6 +1793,10 @@ static int rand_initialize(void)
 	init_std_data(&blocking_pool);
 	crng_initialize(&primary_crng);
 	crng_global_init_time = jiffies;
+	if (ratelimit_disable) {
+		urandom_warning.interval = 0;
+		unseeded_warning.interval = 0;
+	}
 	return 0;
 }
 early_initcall(rand_initialize);
@@ -1836,9 +1864,10 @@ urandom_read(struct file *file, char __u
 
 	if (!crng_ready() && maxwarn > 0) {
 		maxwarn--;
-		printk(KERN_NOTICE "random: %s: uninitialized urandom read "
-		       "(%zd bytes read)\n",
-		       current->comm, nbytes);
+		if (__ratelimit(&urandom_warning))
+			printk(KERN_NOTICE "random: %s: uninitialized "
+			       "urandom read (%zd bytes read)\n",
+			       current->comm, nbytes);
 		spin_lock_irqsave(&primary_crng.lock, flags);
 		crng_init_cnt = 0;
 		spin_unlock_irqrestore(&primary_crng.lock, flags);