From: Amos Kong Subject: [PATCH v5 REPOST 4/6] hw_random: fix unregister race. Date: Mon, 8 Dec 2014 16:50:38 +0800 Message-ID: <1418028640-4891-5-git-send-email-akong@redhat.com> References: <1418028640-4891-1-git-send-email-akong@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: herbert@gondor.apana.org.au, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, m@bues.ch, mpm@selenic.com, amit.shah@redhat.com To: linux-crypto@vger.kernel.org Return-path: In-Reply-To: <1418028640-4891-1-git-send-email-akong@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: linux-crypto.vger.kernel.org From: Rusty Russell The previous patch added one potential problem: we can still be reading from a hwrng when it's unregistered. Add a wait for zero in the hwrng_unregister path. v5: reset cleanup_done flag, use compiler barrier to prevent recording. v4: add cleanup_done flag to insure that cleanup is done Signed-off-by: Rusty Russell Signed-off-by: Amos Kong --- drivers/char/hw_random/core.c | 12 ++++++++++++ include/linux/hw_random.h | 1 + 2 files changed, 13 insertions(+) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 83516cb..067270b 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -60,6 +60,7 @@ static DEFINE_MUTEX(rng_mutex); static DEFINE_MUTEX(reading_mutex); static int data_avail; static u8 *rng_buffer, *rng_fillbuf; +static DECLARE_WAIT_QUEUE_HEAD(rng_done); static unsigned short current_quality; static unsigned short default_quality; /* = 0; default to "off" */ @@ -98,6 +99,11 @@ static inline void cleanup_rng(struct kref *kref) if (rng->cleanup) rng->cleanup(rng); + + /* cleanup_done should be updated after cleanup finishes */ + smp_wmb(); + rng->cleanup_done = true; + wake_up_all(&rng_done); } static void set_current_rng(struct hwrng *rng) @@ -498,6 +504,8 @@ int hwrng_register(struct hwrng *rng) add_early_randomness(rng); } + rng->cleanup_done = false; + out_unlock: mutex_unlock(&rng_mutex); out: @@ -529,6 +537,10 @@ void hwrng_unregister(struct hwrng *rng) kthread_stop(hwrng_fill); } else mutex_unlock(&rng_mutex); + + /* Just in case rng is reading right now, wait. */ + wait_event(rng_done, rng->cleanup_done && + atomic_read(&rng->ref.refcount) == 0); } EXPORT_SYMBOL_GPL(hwrng_unregister); diff --git a/include/linux/hw_random.h b/include/linux/hw_random.h index c212e71..7832e50 100644 --- a/include/linux/hw_random.h +++ b/include/linux/hw_random.h @@ -46,6 +46,7 @@ struct hwrng { /* internal. */ struct list_head list; struct kref ref; + bool cleanup_done; }; /** Register a new Hardware Random Number Generator driver. */ -- 1.9.3