[PATCH v5 REPOST 4/6] hw_random: fix unregister race.
From: Amos Kong <hidden>
Date: 2014-12-08 08:53:44
Also in:
kvm, linux-crypto, lkml
Subsystem:
hardware random number generator core, the rest · Maintainers:
Olivia Mackall, Herbert Xu, Linus Torvalds
From: Rusty Russell <redacted> 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 <redacted> Signed-off-by: Amos Kong <redacted> --- 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