This is a note to let you know that I've just added the patch titled random: fix data race on crng init time to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: random-fix-data-race-on-crng-init-time.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 009ba8568be497c640cab7571f7bfd18345d7b24 Mon Sep 17 00:00:00 2001 From: Eric Biggers <ebiggers@xxxxxxxxxx> Date: Mon, 20 Dec 2021 16:41:57 -0600 Subject: random: fix data race on crng init time From: Eric Biggers <ebiggers@xxxxxxxxxx> commit 009ba8568be497c640cab7571f7bfd18345d7b24 upstream. _extract_crng() does plain loads of crng->init_time and crng_global_init_time, which causes undefined behavior if crng_reseed() and RNDRESEEDCRNG modify these corrently. Use READ_ONCE() and WRITE_ONCE() to make the behavior defined. Don't fix the race on crng->init_time by protecting it with crng->lock, since it's not a problem for duplicate reseedings to occur. I.e., the lockless access with READ_ONCE() is fine. Fixes: d848e5f8e1eb ("random: add new ioctl RNDRESEEDCRNG") Fixes: e192be9d9a30 ("random: replace non-blocking pool with a Chacha20-based CRNG") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/char/random.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -908,7 +908,7 @@ static void crng_reseed(struct crng_stat crng->state[i+4] ^= buf.key[i] ^ rv; } memzero_explicit(&buf, sizeof(buf)); - crng->init_time = jiffies; + WRITE_ONCE(crng->init_time, jiffies); if (crng == &primary_crng && crng_init < 2) { numa_crng_init(); crng_init = 2; @@ -946,12 +946,15 @@ static inline void crng_wait_ready(void) static void _extract_crng(struct crng_state *crng, __u8 out[CHACHA20_BLOCK_SIZE]) { - unsigned long v, flags; + unsigned long v, flags, init_time; - if (crng_ready() && - (time_after(crng_global_init_time, crng->init_time) || - time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL))) - crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL); + if (crng_ready()) { + init_time = READ_ONCE(crng->init_time); + if (time_after(READ_ONCE(crng_global_init_time), init_time) || + time_after(jiffies, init_time + CRNG_RESEED_INTERVAL)) + crng_reseed(crng, crng == &primary_crng ? + &input_pool : NULL); + } spin_lock_irqsave(&crng->lock, flags); if (arch_get_random_long(&v)) crng->state[14] ^= v; @@ -1916,7 +1919,7 @@ static long random_ioctl(struct file *f, if (crng_init < 2) return -ENODATA; crng_reseed(&primary_crng, &input_pool); - crng_global_init_time = jiffies - 1; + WRITE_ONCE(crng_global_init_time, jiffies - 1); return 0; default: return -EINVAL; Patches currently in stable-queue which might be from ebiggers@xxxxxxxxxx are queue-4.9/random-fix-data-race-on-crng-init-time.patch queue-4.9/random-fix-data-race-on-crng_node_pool.patch