[PATCH 4.9 018/264] random: set up the NUMA crng instances after the CRNG is fully initialized

Greg Kroah-Hartman
2022-06-23T16:47:15Z

From: Theodore Ts'o <tytso@mit.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@google.com>
Fixes: 1e7f583af67b ("random: make /dev/urandom scalable for silly...")
Cc: stable@kernel.org # 4.8+
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -799,6 +799,32 @@ static void crng_initialize(struct crng_
crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 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
+
/*
* crng_fast_load() can be called by code in the interrupt service
* path. So we can't afford to dilly-dally.
@@ -957,6 +983,7 @@ static void crng_reseed(struct crng_stat
if (crng == &primary_crng && crng_init < 2) {
numa_crng_init();
invalidate_batched_entropy();
+ numa_crng_init();
crng_init = 2;
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);