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random: set up the NUMA crng instances after the CRNG is fully initialized

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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: 1e7f583af6 ("random: make /dev/urandom scalable for silly...")
Cc: stable@kernel.org # 4.8+
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2018-04-11 15:23:56 -04:00
parent dc12baacb9
commit 8ef35c866f
1 changed files with 27 additions and 19 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

46
drivers/char/random.c
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@ -787,6 +787,32 @@ static void crng_initialize(struct crng_state *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.
@ -893,6 +919,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
spin_unlock_irqrestore(&primary_crng.lock, flags);
if (crng == &primary_crng && crng_init < 2) {
invalidate_batched_entropy();
numa_crng_init();
crng_init = 2;
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);
@ -1727,28 +1754,9 @@ static void init_std_data(struct entropy_store *r)
*/
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);