random: clamp credited irq bits to maximum mixed

BugLink: https://bugs.launchpad.net/bugs/1995638
commit e78a802a7b4febf53f2a92842f494b01062d85a8 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 50dc861f183b6c3b23b461910b8c663ac5598d9f..5b2950473c19b595a78f0ec8fb8ebb57e6e36248 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -980,7 +980,7 @@ 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));
 }