From: Eric Biggers <ebiggers@kernel.org>
To: Theodore Ts'o <tytso@mit.edu>, "Jason A . Donenfeld " <Jason@zx2c4.com>
Cc: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
"Paul E . McKenney" <paulmck@kernel.org>,
stable@vger.kernel.org
Subject: [PATCH v2 1/2] random: fix data race on crng_node_pool
Date: Mon, 20 Dec 2021 16:41:56 -0600 [thread overview]
Message-ID: <20211220224157.111959-2-ebiggers@kernel.org> (raw)
In-Reply-To: <20211220224157.111959-1-ebiggers@kernel.org>
From: Eric Biggers <ebiggers@google.com>
extract_crng() and crng_backtrack_protect() load crng_node_pool with a
plain load, which causes undefined behavior if do_numa_crng_init()
modifies it concurrently.
Fix this by using READ_ONCE(). Note: as per the previous discussion
https://lore.kernel.org/lkml/20211219025139.31085-1-ebiggers@kernel.org/T/#u,
READ_ONCE() is believed to be sufficient here, and it was requested that
it be used here instead of smp_load_acquire().
Also change do_numa_crng_init() to set crng_node_pool using
cmpxchg_release() instead of mb() + cmpxchg(), as the former is
sufficient here but is more lightweight.
Fixes: 1e7f583af67b ("random: make /dev/urandom scalable for silly userspace programs")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
drivers/char/random.c | 42 ++++++++++++++++++++++--------------------
1 file changed, 22 insertions(+), 20 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 605969ed0f96..1294b4527cdd 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -843,8 +843,8 @@ static void do_numa_crng_init(struct work_struct *work)
crng_initialize_secondary(crng);
pool[i] = crng;
}
- mb();
- if (cmpxchg(&crng_node_pool, NULL, pool)) {
+ /* pairs with READ_ONCE() in select_crng() */
+ if (cmpxchg_release(&crng_node_pool, NULL, pool) != NULL) {
for_each_node(i)
kfree(pool[i]);
kfree(pool);
@@ -857,8 +857,26 @@ static void numa_crng_init(void)
{
schedule_work(&numa_crng_init_work);
}
+
+static struct crng_state *select_crng(void)
+{
+ struct crng_state **pool;
+ int nid = numa_node_id();
+
+ /* pairs with cmpxchg_release() in do_numa_crng_init() */
+ pool = READ_ONCE(crng_node_pool);
+ if (pool && pool[nid])
+ return pool[nid];
+
+ return &primary_crng;
+}
#else
static void numa_crng_init(void) {}
+
+static struct crng_state *select_crng(void)
+{
+ return &primary_crng;
+}
#endif
/*
@@ -1005,15 +1023,7 @@ static void _extract_crng(struct crng_state *crng,
static void extract_crng(__u8 out[CHACHA_BLOCK_SIZE])
{
- struct crng_state *crng = NULL;
-
-#ifdef CONFIG_NUMA
- if (crng_node_pool)
- crng = crng_node_pool[numa_node_id()];
- if (crng == NULL)
-#endif
- crng = &primary_crng;
- _extract_crng(crng, out);
+ _extract_crng(select_crng(), out);
}
/*
@@ -1042,15 +1052,7 @@ static void _crng_backtrack_protect(struct crng_state *crng,
static void crng_backtrack_protect(__u8 tmp[CHACHA_BLOCK_SIZE], int used)
{
- struct crng_state *crng = NULL;
-
-#ifdef CONFIG_NUMA
- if (crng_node_pool)
- crng = crng_node_pool[numa_node_id()];
- if (crng == NULL)
-#endif
- crng = &primary_crng;
- _crng_backtrack_protect(crng, tmp, used);
+ _crng_backtrack_protect(select_crng(), tmp, used);
}
static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
--
2.34.1
next prev parent reply other threads:[~2021-12-20 22:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-20 22:41 [PATCH v2 0/2] random: fix some data races Eric Biggers
2021-12-20 22:41 ` Eric Biggers [this message]
2021-12-20 22:41 ` [PATCH v2 2/2] random: fix data race on crng init time Eric Biggers
2021-12-20 23:40 ` [PATCH v2 0/2] random: fix some data races Paul E. McKenney
2021-12-21 12:15 ` Jason A. Donenfeld
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