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Subject[PATCH] random: check for signal and try earlier when generating entropy
Date
We call try_to_generate_entropy() from wait_for_random_bytes().
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. When entering a busy loop in
try_to_generate_entropy(), we should therefore also check to see if any
signals are pending, so that a process doesn't get stuck in that loop
longer than expected. As well, there's no point in waiting for a full
second before trying to generate entropy; instead do it in the opposite
order, where we try to generate, and then go into the waitable.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
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 edb5b06544da..4c5f515b6080 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -128,11 +128,12 @@ int wait_for_random_bytes(void)

do {
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();
} while (!crng_ready());

return 0;
@@ -1374,7 +1375,7 @@ 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));
--
2.35.1
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