From: Herbert Xu Subject: [PATCH 2/5] hwrng: core - Fix current_rng init/cleanup race yet again Date: Tue, 23 Dec 2014 16:40:18 +1100 Message-ID: References: <20141223053909.GA28001@gondor.apana.org.au> To: Fengguang Wu , Rusty Russell , LKP , linux-kernel@vger.kernel.org, Linux Crypto Mailing List , Amos Kong , m@bues.ch, mpm@selenic.com, amit.shah@redhat.com Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org The kref solution is still buggy because we were only focusing on the register/unregister race. The same race affects the setting of current_rng through sysfs. This patch fixes it by using kref_get_unless_zero. Signed-off-by: Herbert Xu --- drivers/char/hw_random/core.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 3dba2cf..42827fd 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -105,7 +105,6 @@ static inline void cleanup_rng(struct kref *kref) static void set_current_rng(struct hwrng *rng) { BUG_ON(!mutex_is_locked(&rng_mutex)); - kref_get(&rng->ref); current_rng = rng; } @@ -150,6 +149,9 @@ static void put_rng(struct hwrng *rng) static inline int hwrng_init(struct hwrng *rng) { + if (kref_get_unless_zero(&rng->ref)) + goto skip_init; + if (rng->init) { int ret; @@ -157,6 +159,11 @@ static inline int hwrng_init(struct hwrng *rng) if (ret) return ret; } + + kref_init(&rng->ref); + reinit_completion(&rng->cleanup_done); + +skip_init: add_early_randomness(rng); current_quality = rng->quality ? : default_quality; @@ -467,6 +474,9 @@ int hwrng_register(struct hwrng *rng) goto out_unlock; } + init_completion(&rng->cleanup_done); + complete(&rng->cleanup_done); + old_rng = current_rng; err = 0; if (!old_rng) { @@ -494,8 +504,6 @@ int hwrng_register(struct hwrng *rng) add_early_randomness(rng); } - init_completion(&rng->cleanup_done); - out_unlock: mutex_unlock(&rng_mutex); out: