habanalabs: use default structure for user input in Debug IOCTL

This patch fixes a possible kernel crash when a user provides a too small
input structure to the Debug IOCTL.
The fix sets a default input structure and copies to it the user data.
In case the user provided as input a too small structure, the code will
use the default values taken from the default structure.
Note that in contrary to the input structure, the user can provide an
output structure with changing size or no size at all. Therefore the user
output structure validation is already done in the Debug logic later on.
Signed-off-by: Omer Shpigelman <oshpigelman@habana.ai>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>

drivers/misc/habanalabs/habanalabs_ioctl.c

@@ -144,13 +144,16 @@ static int debug_coresight(struct hl_device *hdev, struct hl_debug_args *args)
 	params->op = args->op;
 
 	if (args->input_ptr && args->input_size) {
-		input = memdup_user(u64_to_user_ptr(args->input_ptr),
-					args->input_size);
-		if (IS_ERR(input)) {
-			rc = PTR_ERR(input);
-			input = NULL;
-			dev_err(hdev->dev,
-				"error %d when copying input debug data\n", rc);
+		input = kzalloc(hl_debug_struct_size[args->op], GFP_KERNEL);
+		if (!input) {
+			rc = -ENOMEM;
+			goto out;
+		}
+
+		if (copy_from_user(input, u64_to_user_ptr(args->input_ptr),
+					args->input_size)) {
+			rc = -EFAULT;
+			dev_err(hdev->dev, "failed to copy input debug data\n");
 			goto out;
 		}