From 837bf7cc3b7504385ae0e829c72e470dfc27cf6c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michael=20B=C3=BCsch?= <m@bues.ch>
Date: Thu, 14 Jun 2018 20:08:11 +0200
Subject: [PATCH] hwrng: core - Always drop the RNG in hwrng_unregister()
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enable_best_rng() is used in hwrng_unregister() to switch away from the
currently active RNG, if that is the one currently being removed.
However enable_best_rng() might fail, if the next RNG's init routine
fails. In that case enable_best_rng() will return an error code and
the currently active RNG will remain active.
After unregistering this might lead to crashes due to use-after-free.
Fix this by dropping the currently active RNG, if enable_best_rng()
failed. This will result in no RNG to be active, if the next-best
one failed to initialize.
This problem was introduced by 142a27f0a731ddcf467546960a5585970ca98e21
Fixes: 142a27f0a731 ("hwrng: core - Reset user selected rng by...")
Reported-by: Wirz <spam@lukas-wirz.de>
Tested-by: Wirz <spam@lukas-wirz.de>
Signed-off-by: Michael Büsch <m@bues.ch>
Cc: stable@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---
drivers/char/hw_random/core.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 91bb98c42a1ca7..aaf9e5afaad435 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -516,11 +516,18 @@ EXPORT_SYMBOL_GPL(hwrng_register);
void hwrng_unregister(struct hwrng *rng)
{
+ int err;
+
mutex_lock(&rng_mutex);
list_del(&rng->list);
- if (current_rng == rng)
- enable_best_rng();
+ if (current_rng == rng) {
+ err = enable_best_rng();
+ if (err) {
+ drop_current_rng();
+ cur_rng_set_by_user = 0;
+ }
+ }
if (list_empty(&rng_list)) {
mutex_unlock(&rng_mutex);
--
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