diag: Synchronize command registration table access

Currently, command registration table is being read
in debugfs without any protection which may lead to
access of stale entries. The patch takes care of the
issue by adding proper protection.

CRs-Fixed: 2032672
Change-Id: I6ae058c16873f9ed52ae6516a1a70fd6d2d0da80
Signed-off-by: Mohit Aggarwal <[email protected]>

Author: Mohit Aggarwal

drivers/char/diag/diag_debugfs.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2011-2016, The Linux Foundation. All rights reserved.
+/* Copyright (c) 2011-2017, The Linux Foundation. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 and
@@ -256,8 +256,10 @@ static ssize_t diag_dbgfs_read_table(struct file *file, char __user *ubuf,
 	struct list_head *temp;
 	struct diag_cmd_reg_t *item = NULL;
 
+	mutex_lock(&driver->cmd_reg_mutex);
 	if (diag_dbgfs_table_index == driver->cmd_reg_count) {
 		diag_dbgfs_table_index = 0;
+		mutex_unlock(&driver->cmd_reg_mutex);
 		return 0;
 	}
 
@@ -266,6 +268,7 @@ static ssize_t diag_dbgfs_read_table(struct file *file, char __user *ubuf,
 	buf = kzalloc(sizeof(char) * buf_size, GFP_KERNEL);
 	if (ZERO_OR_NULL_PTR(buf)) {
 		pr_err("diag: %s, Error allocating memory\n", __func__);
+		mutex_unlock(&driver->cmd_reg_mutex);
 		return -ENOMEM;
 	}
 	buf_size = ksize(buf);
@@ -310,6 +313,7 @@ static ssize_t diag_dbgfs_read_table(struct file *file, char __user *ubuf,
 			break;
 	}
 	diag_dbgfs_table_index = i;
+	mutex_unlock(&driver->cmd_reg_mutex);
 
 	*ppos = 0;
 	ret = simple_read_from_buffer(ubuf, count, ppos, buf, bytes_in_buffer);