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authorJason A. Donenfeld <Jason@zx2c4.com>2022-05-09 14:40:55 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2022-05-30 10:24:07 +0300
commite84123f90491618c6d0095495502e566bc5b41c4 (patch)
treefa212c52106a457819d438f9653bbd27e8a0d6d3 /drivers/char/random.c
parenta199b1cf0d53b2da8994b084cd25a84f26cb462a (diff)
downloadlinux-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.c10
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));