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

Signed-off-by: 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. It applies from 3.18 to 4.11, although with a trivial conflict resolution for the later branches. 4c23cbff073f3b9b ("staging: android: ion: Remove import interface")

drivers/staging/android/ion/ion.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c index 374f840f31a48..11f93a6314fdb 100644 --- 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 +388,15 @@ static void ion_handle_get(struct ion_handle *handle) 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 +443,9 @@ static struct ion_handle *ion_handle_get_by_id_nolock(struct ion_client *client,

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 +1212,7 @@ struct ion_handle *ion_import_dma_buf(struct ion_client *client, int fd) /* 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; }