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 142a27f0 Fixes: 142a27f0 ("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>
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