linux-kernel - [PATCH 027/115] gpu: ion: Fix race between ion_import and ion

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Message-Id: <1386973529-4884-28-git-send-email-john.stultz@linaro.org>
Date:	Fri, 13 Dec 2013 14:24:01 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Jesse Barker <jesse.barker@....com>,
	Colin Cross <ccross@...roid.com>,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	John Stultz <john.stultz@...aro.org>
Subject: [PATCH 027/115] gpu: ion: Fix race between ion_import and ion_free

From: Rebecca Schultz Zavin <rebecca@...roid.com>

If preemted during ion_free after the refcount is updated but
before the handle can be removed from the rb_tree, import
might find that handle in the tree and try to reuse it
when execution returns to free, the handle will be cleaned
up leaving the caller of import with a corrupt handle.
This patch modifies the locking to protect agains this race.

Signed-off-by: Rebecca Schultz Zavin <rebecca@...roid.com>
[jstultz: modified patch to apply to staging directory]
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 drivers/staging/android/ion/ion.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index 84229bd..f7dc821 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -253,8 +253,6 @@ static void ion_handle_destroy(struct kref *kref)
 	struct ion_client *client = handle->client;
 	struct ion_buffer *buffer = handle->buffer;
 
-	mutex_lock(&client->lock);
-
 	mutex_lock(&buffer->lock);
 	while (handle->kmap_cnt)
 		ion_handle_kmap_put(handle);
@@ -262,7 +260,6 @@ static void ion_handle_destroy(struct kref *kref)
 
 	if (!RB_EMPTY_NODE(&handle->node))
 		rb_erase(&handle->node, &client->handles);
-	mutex_unlock(&client->lock);
 
 	ion_buffer_put(buffer);
 	kfree(handle);
@@ -406,13 +403,13 @@ void ion_free(struct ion_client *client, struct ion_handle *handle)
 
 	mutex_lock(&client->lock);
 	valid_handle = ion_handle_validate(client, handle);
-	mutex_unlock(&client->lock);
 
 	if (!valid_handle) {
 		WARN(1, "%s: invalid handle passed to free.\n", __func__);
 		return;
 	}
 	ion_handle_put(handle);
+	mutex_unlock(&client->lock);
 }
 EXPORT_SYMBOL(ion_free);
 
-- 
1.8.3.2

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