msm: kgsl: Correct the refcount on current process PID

In kgsl_process_private_new() function there is inconsistency
in the refcount of current process PID. Fix this to avoid
overflowing of reference counter leading to use after free
of this struct.

Change-Id: I6291b9a05e139337e7f8471d0f9409fc839969a3
Signed-off-by: Archana Sriram <apsrir@codeaurora.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/drivers/gpu/msm/kgsl.c b/drivers/gpu/msm/kgsl.c
index 9d9836052158..268e7231162a 100644
--- a/drivers/gpu/msm/kgsl.c
+++ b/drivers/gpu/msm/kgsl.c
@@ -916,17 +916,24 @@ static struct kgsl_process_private *kgsl_process_private_new(
 	list_for_each_entry(private, &kgsl_driver.process_list, list) {
 		if (private->pid == cur_pid) {
 			if (!kgsl_process_private_get(private)) {
-				put_pid(cur_pid);
 				private = ERR_PTR(-EINVAL);
 			}
+			/*
+			 * We need to hold only one reference to the PID for
+			 * each process struct to avoid overflowing the
+			 * reference counter which can lead to use-after-free.
+			 */
+			put_pid(cur_pid);
 			return private;
 		}
 	}
 
 	/* Create a new object */
 	private = kzalloc(sizeof(struct kgsl_process_private), GFP_KERNEL);
-	if (private == NULL)
+	if (private == NULL) {
+		put_pid(cur_pid);
 		return ERR_PTR(-ENOMEM);
+	}
 
 	kref_init(&private->refcount);