[PATCH 4.4 66/79] staging: android: ion: check for kref overflow

Greg Kroah-Hartman
2018-08-23T08:01:18Z

From: Daniel Rosenberg <drosen@google.com>

This patch is against 4.4. 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>
---
v2: Fixed patch corruption :(

It applies from 3.18 to 4.11, although with a trivial conflict resolution
for the later branches.
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>
@@ -387,6 +388,16 @@ 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;
+}
+
static int ion_handle_put_nolock(struct ion_handle *handle)
{
int ret;
@@ -433,9 +444,9 @@ static struct ion_handle *ion_handle_get

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);
}

struct ion_handle *ion_handle_get_by_id(struct ion_client *client,
@@ -1202,7 +1213,7 @@ 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;
}