[PATCH] staging: android: ion: check for kref overflow

[Daniel Rosenberg]

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

diff --git a/drivers/staging/android/ion/ion.c 
b/drivers/staging/android/ion/ion.c
index 6f9974cb0e152..48821948fa487 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>
@@ -305,6 +306,16 @@ 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;
+}
+
 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_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,
@@ -1100,7 +1111,7 @@ struct ion_handle *ion_import_dma_buf(struct ion_client 
*client,
        /* 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;
        }
-- 
2.19.0.rc0.228.g281dcd1b4d0-goog