diff options
author | Jason A. Donenfeld <Jason@zx2c4.com> | 2022-05-09 14:40:55 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-05-30 10:24:07 +0300 |
commit | e84123f90491618c6d0095495502e566bc5b41c4 (patch) | |
tree | fa212c52106a457819d438f9653bbd27e8a0d6d3 /drivers/char/random.c | |
parent | a199b1cf0d53b2da8994b084cd25a84f26cb462a (diff) | |
download | linux-e84123f90491618c6d0095495502e566bc5b41c4.tar.xz |
random: avoid initializing twice in credit race
commit fed7ef061686cc813b1f3d8d0edc6c35b4d3537b upstream.
Since all changes of crng_init now go through credit_init_bits(), we can
fix a long standing race in which two concurrent callers of
credit_init_bits() have the new bit count >= some threshold, but are
doing so with crng_init as a lower threshold, checked outside of a lock,
resulting in crng_reseed() or similar being called twice.
In order to fix this, we can use the original cmpxchg value of the bit
count, and only change crng_init when the bit count transitions from
below a threshold to meeting the threshold.
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/char/random.c')
-rw-r--r-- | drivers/char/random.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index a22122b50a63..d9b76f44135d 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -821,7 +821,7 @@ static void extract_entropy(void *buf, size_t nbytes) static void credit_init_bits(size_t nbits) { - unsigned int init_bits, orig, add; + unsigned int new, orig, add; unsigned long flags; if (crng_ready() || !nbits) @@ -831,12 +831,12 @@ static void credit_init_bits(size_t nbits) do { orig = READ_ONCE(input_pool.init_bits); - init_bits = min_t(unsigned int, POOL_BITS, orig + add); - } while (cmpxchg(&input_pool.init_bits, orig, init_bits) != orig); + new = min_t(unsigned int, POOL_BITS, orig + add); + } while (cmpxchg(&input_pool.init_bits, orig, new) != orig); - if (!crng_ready() && init_bits >= POOL_READY_BITS) + if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) crng_reseed(); - else if (unlikely(crng_init == CRNG_EMPTY && init_bits >= POOL_EARLY_BITS)) { + else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) { spin_lock_irqsave(&base_crng.lock, flags); if (crng_init == CRNG_EMPTY) { extract_entropy(base_crng.key, sizeof(base_crng.key)); |