random: clamp credited irq bits to maximum mixed

Since the most that's mixed into the pool is sizeof(long)*2, don't
credit more than that many bytes of entropy.

Fixes: e3e33fc2ea7f ("random: do not use input pool from hard IRQs")
Cc: stable@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 520a385c7dab8df9c6a04dc693d995b26c0bad42..2f370aa248b22ae1970b5f4131db49b27cd46e19 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1004,7 +1004,7 @@ static void mix_interrupt_randomness(struct work_struct *work)
        local_irq_enable();
 
        mix_pool_bytes(pool, sizeof(pool));
-       credit_init_bits(max(1u, (count & U16_MAX) / 64));
+       credit_init_bits(clamp_t(unsigned int, (count & U16_MAX) / 64, 1, sizeof(pool) * 8));
 
        memzero_explicit(pool, sizeof(pool));
 }