linux-kernel - [PATCH 4.9 75/95] random: set up the NUMA crng instances after the CRNG is fully initialized

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Date:   Sun, 22 Apr 2018 15:53:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        Theodore Tso <tytso@....edu>, stable@...nel.org
Subject: [PATCH 4.9 75/95] random: set up the NUMA crng instances after the CRNG is fully initialized

4.9-stable review patch.  If anyone has any objections, please let me know.

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

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

commit 8ef35c866f8862df074a49a93b0309725812dea8 upstream.

Until the primary_crng is fully initialized, don't initialize the NUMA
crng nodes.  Otherwise users of /dev/urandom on NUMA systems before
the CRNG is fully initialized can get very bad quality randomness.  Of
course everyone should move to getrandom(2) where this won't be an
issue, but there's a lot of legacy code out there.  This related to
CVE-2018-1108.

Reported-by: Jann Horn <jannh@...gle.com>
Fixes: 1e7f583af67b ("random: make /dev/urandom scalable for silly...")
Cc: stable@...nel.org # 4.8+
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/char/random.c |   46 +++++++++++++++++++++++++++-------------------
 1 file changed, 27 insertions(+), 19 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -818,6 +818,32 @@ static int crng_fast_load(const char *cp
 	return 1;
 }
 
+#ifdef CONFIG_NUMA
+static void numa_crng_init(void)
+{
+	int i;
+	struct crng_state *crng;
+	struct crng_state **pool;
+
+	pool = kcalloc(nr_node_ids, sizeof(*pool), GFP_KERNEL|__GFP_NOFAIL);
+	for_each_online_node(i) {
+		crng = kmalloc_node(sizeof(struct crng_state),
+				    GFP_KERNEL | __GFP_NOFAIL, i);
+		spin_lock_init(&crng->lock);
+		crng_initialize(crng);
+		pool[i] = crng;
+	}
+	mb();
+	if (cmpxchg(&crng_node_pool, NULL, pool)) {
+		for_each_node(i)
+			kfree(pool[i]);
+		kfree(pool);
+	}
+}
+#else
+static void numa_crng_init(void) {}
+#endif
+
 static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
 {
 	unsigned long	flags;
@@ -847,6 +873,7 @@ static void crng_reseed(struct crng_stat
 	memzero_explicit(&buf, sizeof(buf));
 	crng->init_time = jiffies;
 	if (crng == &primary_crng && crng_init < 2) {
+		numa_crng_init();
 		crng_init = 2;
 		process_random_ready_list();
 		wake_up_interruptible(&crng_init_wait);
@@ -1659,28 +1686,9 @@ static void init_std_data(struct entropy
  */
 static int rand_initialize(void)
 {
-#ifdef CONFIG_NUMA
-	int i;
-	struct crng_state *crng;
-	struct crng_state **pool;
-#endif
-
 	init_std_data(&input_pool);
 	init_std_data(&blocking_pool);
 	crng_initialize(&primary_crng);
-
-#ifdef CONFIG_NUMA
-	pool = kcalloc(nr_node_ids, sizeof(*pool), GFP_KERNEL|__GFP_NOFAIL);
-	for_each_online_node(i) {
-		crng = kmalloc_node(sizeof(struct crng_state),
-				    GFP_KERNEL | __GFP_NOFAIL, i);
-		spin_lock_init(&crng->lock);
-		crng_initialize(crng);
-		pool[i] = crng;
-	}
-	mb();
-	crng_node_pool = pool;
-#endif
 	return 0;
 }
 early_initcall(rand_initialize);