Patch "staging/android/ion : fix a race condition in the ion driver" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    staging/android/ion : fix a race condition in the ion driver

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     staging-android-ion-fix-a-race-condition-in-the-ion-driver.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 9590232bb4f4cc824f3425a6e1349afbe6d6d2b7 Mon Sep 17 00:00:00 2001
From: EunTaik Lee <eun.taik.lee@samsung.com>
Date: Wed, 24 Feb 2016 04:38:06 +0000
Subject: staging/android/ion : fix a race condition in the ion driver

From: EunTaik Lee <eun.taik.lee@samsung.com>

commit 9590232bb4f4cc824f3425a6e1349afbe6d6d2b7 upstream.

There is a use-after-free problem in the ion driver.
This is caused by a race condition in the ion_ioctl()
function.

A handle has ref count of 1 and two tasks on different
cpus calls ION_IOC_FREE simultaneously.

cpu 0                                   cpu 1
-------------------------------------------------------
ion_handle_get_by_id()
(ref == 2)
                            ion_handle_get_by_id()
                            (ref == 3)

ion_free()
(ref == 2)

ion_handle_put()
(ref == 1)

                            ion_free()
                            (ref == 0 so ion_handle_destroy() is
                            called
                            and the handle is freed.)

                            ion_handle_put() is called and it
                            decreases the slub's next free pointer

The problem is detected as an unaligned access in the
spin lock functions since it uses load exclusive
 instruction. In some cases it corrupts the slub's
free pointer which causes a mis-aligned access to the
next free pointer.(kmalloc returns a pointer like
ffffc0745b4580aa). And it causes lots of other
hard-to-debug problems.

This symptom is caused since the first member in the
ion_handle structure is the reference count and the
ion driver decrements the reference after it has been
freed.

To fix this problem client->lock mutex is extended
to protect all the codes that uses the handle.

Signed-off-by: Eun Taik Lee <eun.taik.lee@samsung.com>
Reviewed-by: Laura Abbott <labbott@redhat.com>
Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

index 7ff2a7ec871f..33b390e7ea31
---
 drivers/staging/android/ion/ion.c |   55 +++++++++++++++++++++++++++++---------
 1 file changed, 42 insertions(+), 13 deletions(-)

--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -387,13 +387,22 @@ static void ion_handle_get(struct ion_ha
 	kref_get(&handle->ref);
 }
 
-static int ion_handle_put(struct ion_handle *handle)
+static int ion_handle_put_nolock(struct ion_handle *handle)
+{
+	int ret;
+
+	ret = kref_put(&handle->ref, ion_handle_destroy);
+
+	return ret;
+}
+
+int ion_handle_put(struct ion_handle *handle)
 {
 	struct ion_client *client = handle->client;
 	int ret;
 
 	mutex_lock(&client->lock);
-	ret = kref_put(&handle->ref, ion_handle_destroy);
+	ret = ion_handle_put_nolock(handle);
 	mutex_unlock(&client->lock);
 
 	return ret;
@@ -417,20 +426,30 @@ static struct ion_handle *ion_handle_loo
 	return ERR_PTR(-EINVAL);
 }
 
-static struct ion_handle *ion_handle_get_by_id(struct ion_client *client,
+static struct ion_handle *ion_handle_get_by_id_nolock(struct ion_client *client,
 						int id)
 {
 	struct ion_handle *handle;
 
-	mutex_lock(&client->lock);
 	handle = idr_find(&client->idr, id);
 	if (handle)
 		ion_handle_get(handle);
-	mutex_unlock(&client->lock);
 
 	return handle ? handle : ERR_PTR(-EINVAL);
 }
 
+struct ion_handle *ion_handle_get_by_id(struct ion_client *client,
+						int id)
+{
+	struct ion_handle *handle;
+
+	mutex_lock(&client->lock);
+	handle = ion_handle_get_by_id_nolock(client, id);
+	mutex_unlock(&client->lock);
+
+	return handle;
+}
+
 static bool ion_handle_validate(struct ion_client *client,
 				struct ion_handle *handle)
 {
@@ -532,22 +551,28 @@ struct ion_handle *ion_alloc(struct ion_
 }
 EXPORT_SYMBOL(ion_alloc);
 
-void ion_free(struct ion_client *client, struct ion_handle *handle)
+static void ion_free_nolock(struct ion_client *client, struct ion_handle *handle)
 {
 	bool valid_handle;
 
 	BUG_ON(client != handle->client);
 
-	mutex_lock(&client->lock);
 	valid_handle = ion_handle_validate(client, handle);
 
 	if (!valid_handle) {
 		WARN(1, "%s: invalid handle passed to free.\n", __func__);
-		mutex_unlock(&client->lock);
 		return;
 	}
+	ion_handle_put_nolock(handle);
+}
+
+void ion_free(struct ion_client *client, struct ion_handle *handle)
+{
+	BUG_ON(client != handle->client);
+
+	mutex_lock(&client->lock);
+	ion_free_nolock(client, handle);
 	mutex_unlock(&client->lock);
-	ion_handle_put(handle);
 }
 EXPORT_SYMBOL(ion_free);
 
@@ -1283,11 +1308,15 @@ static long ion_ioctl(struct file *filp,
 	{
 		struct ion_handle *handle;
 
-		handle = ion_handle_get_by_id(client, data.handle.handle);
-		if (IS_ERR(handle))
+		mutex_lock(&client->lock);
+		handle = ion_handle_get_by_id_nolock(client, data.handle.handle);
+		if (IS_ERR(handle)) {
+			mutex_unlock(&client->lock);
 			return PTR_ERR(handle);
-		ion_free(client, handle);
-		ion_handle_put(handle);
+		}
+		ion_free_nolock(client, handle);
+		ion_handle_put_nolock(handle);
+		mutex_unlock(&client->lock);
 		break;
 	}
 	case ION_IOC_SHARE:


Patches currently in stable-queue which might be from eun.taik.lee@samsung.com are

queue-4.4/staging-android-ion-fix-a-race-condition-in-the-ion-driver.patch