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Subject[PATCH 4.9 107/107] staging: android: ion: check for kref overflow
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Rosenberg <drosen@google.com>

This patch is against 4.9. It does not apply to master due to a large
rework of ion in 4.12 which removed the affected functions altogther.
4c23cbff073f3b9b ("staging: android: ion: Remove import interface")

Userspace can cause the kref to handles to increment
arbitrarily high. Ensure it does not overflow.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/staging/android/ion/ion.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -15,6 +15,7 @@
*
*/

+#include <linux/atomic.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/file.h>
@@ -305,6 +306,16 @@ static void ion_handle_get(struct ion_ha
kref_get(&handle->ref);
}

+/* Must hold the client lock */
+static struct ion_handle *ion_handle_get_check_overflow(
+ struct ion_handle *handle)
+{
+ if (atomic_read(&handle->ref.refcount) + 1 == 0)
+ return ERR_PTR(-EOVERFLOW);
+ ion_handle_get(handle);
+ return handle;
+}
+
int ion_handle_put_nolock(struct ion_handle *handle)
{
return kref_put(&handle->ref, ion_handle_destroy);
@@ -347,9 +358,9 @@ struct ion_handle *ion_handle_get_by_id_

handle = idr_find(&client->idr, id);
if (handle)
- ion_handle_get(handle);
+ return ion_handle_get_check_overflow(handle);

- return handle ? handle : ERR_PTR(-EINVAL);
+ return ERR_PTR(-EINVAL);
}

static bool ion_handle_validate(struct ion_client *client,
@@ -1110,7 +1121,7 @@ struct ion_handle *ion_import_dma_buf(st
/* if a handle exists for this buffer just take a reference to it */
handle = ion_handle_lookup(client, buffer);
if (!IS_ERR(handle)) {
- ion_handle_get(handle);
+ handle = ion_handle_get_check_overflow(handle);
mutex_unlock(&client->lock);
goto end;
}

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