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hwrng: core - Always drop the RNG in hwrng_unregister() 

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 142a27f0a7

Fixes: 142a27f0a7 ("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>
This commit is contained in:
Michael Büsch 2018-06-14 20:08:11 +02:00 committed by Herbert Xu
parent a81ae80957
commit 837bf7cc3b
1 changed files with 9 additions and 2 deletions
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11
drivers/char/hw_random/core.c
View File

@ -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);