linux-kernel - [PATCH v4 4/6] hw_random: fix unregister race.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon,  3 Nov 2014 23:56:24 +0800
From:	Amos Kong <akong@...hat.com>
To:	virtualization@...ts.linux-foundation.org
Cc:	kvm@...r.kernel.org, rusty@...tcorp.com.au,
	herbert@...dor.apana.org.au, m@...s.ch, mb@...sch.de,
	mpm@...enic.com, amit.shah@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH v4 4/6] hw_random: fix unregister race.

From: Rusty Russell <rusty@...tcorp.com.au>

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.

v4: add cleanup_done flag to insure that cleanup is done

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Amos Kong <akong@...hat.com>
---
 drivers/char/hw_random/core.c | 8 ++++++++
 include/linux/hw_random.h     | 1 +
 2 files changed, 9 insertions(+)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 27ad6b4..c31bf91 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 +99,8 @@ static inline void cleanup_rng(struct kref *kref)
 
 	if (rng->cleanup)
 		rng->cleanup(rng);
+	rng->cleanup_done = true;
+	wake_up_all(&rng_done);
 }
 
 static void set_current_rng(struct hwrng *rng)
@@ -536,6 +539,11 @@ 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/