From 3689ac035180926ee70ceede0133d24af4605fa9 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Tue, 8 Mar 2022 10:12:16 -0700
Subject: [PATCH] random: check for signal and try earlier when generating
entropy
commit 3e504d2026eb6c8762cd6040ae57db166516824a upstream.
Rather than waiting a full second in an interruptable waiter before
trying to generate entropy, try to generate entropy first and wait
second. While waiting one second might give an extra second for getting
entropy from elsewhere, we're already pretty late in the init process
here, and whatever else is generating entropy will still continue to
contribute. This has implications on signal handling: we call
try_to_generate_entropy() from wait_for_random_bytes(), and
wait_for_random_bytes() always uses wait_event_interruptible_timeout()
when waiting, since it's called by userspace code in restartable
contexts, where signals can pend. Since try_to_generate_entropy() now
runs first, if a signal is pending, it's necessary for
try_to_generate_entropy() to check for signals, since it won't hit the
wait until after try_to_generate_entropy() has returned. And even before
this change, when entering a busy loop in try_to_generate_entropy(), we
should have been checking to see if any signals are pending, so that a
process doesn't get stuck in that loop longer than expected.
Cc: Theodore Ts'o <tytso@mit.edu>
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>
---
drivers/char/random.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 4187cc8e4cb74..4c0a12c9052bc 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -127,10 +127,11 @@ int wait_for_random_bytes(void)
{
while (!crng_ready()) {
int ret;
+
+ try_to_generate_entropy();
ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
if (ret)
return ret > 0 ? 0 : ret;
- try_to_generate_entropy();
}
return 0;
}
@@ -1371,7 +1372,7 @@ static void try_to_generate_entropy(void)
return;
timer_setup_on_stack(&stack.timer, entropy_timer, 0);
- while (!crng_ready()) {
+ while (!crng_ready() && !signal_pending(current)) {
if (!timer_pending(&stack.timer))
mod_timer(&stack.timer, jiffies + 1);
mix_pool_bytes(&stack.cycles, sizeof(stack.cycles));
--
2.30.2