From f4f7c153a61782f3fb259d0f39aab91444e555d9 Mon Sep 17 00:00:00 2001 From: Dominik Brodowski Date: Mon, 24 Jan 2022 21:29:50 +0100 Subject: [PATCH] hwrng: core - break out of hwrng_fillfn if current rng is not trusted For two reasons, current_quality may become zero within the rngd kernel thread: (1) The user lowers current_quality to 0 by writing to the sysfs module parameter file (note that increasing the quality from zero is without effect at the moment), or (2) there are two or more hwrng devices registered, and those which provide quality>0 are unregistered, but one with quality==0 remains. If current_quality is 0, the randomness is not trusted and cannot help to increase the entropy count. That will lead to continuous calls to the hwrngd thread and continuous stirring of the input pool with untrusted bits. Cc: Matt Mackall Cc: Herbert Xu Cc: Jason A. Donenfeld Signed-off-by: Dominik Brodowski Signed-off-by: Herbert Xu --- drivers/char/hw_random/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 9405fcdace384..bc9f95cbac921 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -429,6 +429,9 @@ static int hwrng_fillfn(void *unused) while (!kthread_should_stop()) { struct hwrng *rng; + if (!current_quality) + break; + rng = get_current_rng(); if (IS_ERR(rng) || !rng) break; -- 2.30.2