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 Reported-by: Wirz <[email protected]> Tested-by: Wirz <[email protected]> Signed-off-by: Michael Büsch <[email protected]> Cc: [email protected] --- See this discussion for a crash in b43's hwrng caused by this problem: https://www.spinics.net/lists/linux-wireless/msg173089.html diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 91bb98c42a1c..aaf9e5afaad4 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); -- Michael
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