net: hns3: fix race condition in debugfs

When multiple threads concurrently access the debugfs content, data
and pointer exceptions may occur. Therefore, mutex lock protection is
added for debugfs.

Fixes: 5e69ea7e ("net: hns3: refactor the debugfs process")
Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/hisilicon/hns3/hnae3.h

@@ -839,6 +839,8 @@ struct hnae3_handle {
 
 	u8 netdev_flags;
 	struct dentry *hnae3_dbgfs;
+	/* protects concurrent contention between debugfs commands */
+	struct mutex dbgfs_lock;
 
 	/* Network interface message level enabled bits */
 	u32 msg_enable;

drivers/net/ethernet/hisilicon/hns3/hns3_debugfs.c

@@ -1226,6 +1226,7 @@ static ssize_t hns3_dbg_read(struct file *filp, char __user *buffer,
 	if (ret)
 		return ret;
 
+	mutex_lock(&handle->dbgfs_lock);
 	save_buf = &hns3_dbg_cmd[index].buf;
 
 	if (!test_bit(HNS3_NIC_STATE_INITED, &priv->state) ||
@@ -1238,15 +1239,15 @@ static ssize_t hns3_dbg_read(struct file *filp, char __user *buffer,
 		read_buf = *save_buf;
 	} else {
 		read_buf = kvzalloc(hns3_dbg_cmd[index].buf_len, GFP_KERNEL);
-		if (!read_buf)
-			return -ENOMEM;
+		if (!read_buf) {
+			ret = -ENOMEM;
+			goto out;
+		}
 
 		/* save the buffer addr until the last read operation */
 		*save_buf = read_buf;
-	}
 
-	/* get data ready for the first time to read */
-	if (!*ppos) {
+		/* get data ready for the first time to read */
 		ret = hns3_dbg_read_cmd(dbg_data, hns3_dbg_cmd[index].cmd,
 					read_buf, hns3_dbg_cmd[index].buf_len);
 		if (ret)
@@ -1255,8 +1256,10 @@ static ssize_t hns3_dbg_read(struct file *filp, char __user *buffer,
 
 	size = simple_read_from_buffer(buffer, count, ppos, read_buf,
 				       strlen(read_buf));
-	if (size > 0)
+	if (size > 0) {
+		mutex_unlock(&handle->dbgfs_lock);
 		return size;
+	}
 
 out:
 	/* free the buffer for the last read operation */
@@ -1265,6 +1268,7 @@ static ssize_t hns3_dbg_read(struct file *filp, char __user *buffer,
 		*save_buf = NULL;
 	}
 
+	mutex_unlock(&handle->dbgfs_lock);
 	return ret;
 }
 
@@ -1337,6 +1341,8 @@ int hns3_dbg_init(struct hnae3_handle *handle)
 			debugfs_create_dir(hns3_dbg_dentry[i].name,
 					   handle->hnae3_dbgfs);
 
+	mutex_init(&handle->dbgfs_lock);
+
 	for (i = 0; i < ARRAY_SIZE(hns3_dbg_cmd); i++) {
 		if ((hns3_dbg_cmd[i].cmd == HNAE3_DBG_CMD_TM_NODES &&
 		     ae_dev->dev_version <= HNAE3_DEVICE_VERSION_V2) ||
@@ -1363,6 +1369,7 @@ int hns3_dbg_init(struct hnae3_handle *handle)
 	return 0;
 
 out:
+	mutex_destroy(&handle->dbgfs_lock);
 	debugfs_remove_recursive(handle->hnae3_dbgfs);
 	handle->hnae3_dbgfs = NULL;
 	return ret;
@@ -1378,6 +1385,7 @@ void hns3_dbg_uninit(struct hnae3_handle *handle)
 			hns3_dbg_cmd[i].buf = NULL;
 		}
 
+	mutex_destroy(&handle->dbgfs_lock);
 	debugfs_remove_recursive(handle->hnae3_dbgfs);
 	handle->hnae3_dbgfs = NULL;
 }