During crng_init == 0, we never credit entropy in add_interrupt_ randomness(), but instead dump it directly into the primary_crng. That's fine, except for the fact that we then wind up throwing away that entropy later when we switch to extracting from the input pool and overwriting the primary_crng key. The two other early init sites -- add_hwgenerator_randomness()'s use crng_fast_load() and add_device_ randomness()'s use of crng_slow_load() -- always additionally give their inputs to the input pool. But not add_interrupt_randomness(). This commit fixes that shortcoming by calling mix_pool_bytes() after crng_fast_load() in add_interrupt_randomness(). That's partially verboten on PREEMPT_RT, where it implies taking spinlock_t from an IRQ handler. But this also only happens during early boot and then never again after that. Plus it's a trylock so it has the same considerations as calling crng_fast_load(), which we're already using. Cc: Theodore Ts'o <tytso@xxxxxxx> Reviewed-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> Suggested-by: Eric Biggers <ebiggers@xxxxxxxxxx> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> --- v3 uses a trylock instead of a spinlock, just like all the other locks taken in hard irq. (Incidentally, we're now talking about moving this into the deferred stage, so that at can be a spinlock, but at least with what we have here, this really must be a trylock.) drivers/char/random.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/char/random.c b/drivers/char/random.c index d31b0b3afe2e..f3179c67010b 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -850,6 +850,10 @@ void add_interrupt_randomness(int irq) crng_fast_load((u8 *)fast_pool->pool, sizeof(fast_pool->pool)) > 0) { fast_pool->count = 0; fast_pool->last = now; + if (spin_trylock(&input_pool.lock)) { + _mix_pool_bytes(&fast_pool->pool, sizeof(fast_pool->pool)); + spin_unlock(&input_pool.lock); + } } return; } -- 2.35.0