[S390] hypfs: Move buffer allocation from open to read

Currently the buffer for diagnose data is allocated in the open function
of the debugfs file and is released in the close function. This has the
drawback that a user (root) can pin that memory by not closing the file.
This patch moves the buffer allocation to the read function. The buffer is
automatically released after the buffer is copied to userspace.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 116 insertions, 0 deletions

diff --git a/arch/s390/hypfs/hypfs_dbfs.c b/arch/s390/hypfs/hypfs_dbfs.c
new file mode 100644
index 000000000000..b478013b7fec
--- /dev/null
+++ b/arch/s390/hypfs/hypfs_dbfs.c
@@ -0,0 +1,116 @@
+/*
+ * Hypervisor filesystem for Linux on s390 - debugfs interface
+ *
+ * Copyright (C) IBM Corp. 2010
+ * Author(s): Michael Holzheu <holzheu@linux.vnet.ibm.com>
+ */
+
+#include <linux/slab.h>
+#include "hypfs.h"
+
+static struct dentry *dbfs_dir;
+
+static struct hypfs_dbfs_data *hypfs_dbfs_data_alloc(struct hypfs_dbfs_file *f)
+{
+	struct hypfs_dbfs_data *data;
+
+	data = kmalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return NULL;
+	kref_init(&data->kref);
+	data->dbfs_file = f;
+	return data;
+}
+
+static void hypfs_dbfs_data_free(struct kref *kref)
+{
+	struct hypfs_dbfs_data *data;
+
+	data = container_of(kref, struct hypfs_dbfs_data, kref);
+	data->dbfs_file->data_free(data->buf_free_ptr);
+	kfree(data);
+}
+
+static void data_free_delayed(struct work_struct *work)
+{
+	struct hypfs_dbfs_data *data;
+	struct hypfs_dbfs_file *df;
+
+	df = container_of(work, struct hypfs_dbfs_file, data_free_work.work);
+	mutex_lock(&df->lock);
+	data = df->data;
+	df->data = NULL;
+	mutex_unlock(&df->lock);
+	kref_put(&data->kref, hypfs_dbfs_data_free);
+}
+
+static ssize_t dbfs_read(struct file *file, char __user *buf,
+			 size_t size, loff_t *ppos)
+{
+	struct hypfs_dbfs_data *data;
+	struct hypfs_dbfs_file *df;
+	ssize_t rc;
+
+	if (*ppos != 0)
+		return 0;
+
+	df = file->f_path.dentry->d_inode->i_private;
+	mutex_lock(&df->lock);
+	if (!df->data) {
+		data = hypfs_dbfs_data_alloc(df);
+		if (!data) {
+			mutex_unlock(&df->lock);
+			return -ENOMEM;
+		}
+		rc = df->data_create(&data->buf, &data->buf_free_ptr,
+				     &data->size);
+		if (rc) {
+			mutex_unlock(&df->lock);
+			kfree(data);
+			return rc;
+		}
+		df->data = data;
+		schedule_delayed_work(&df->data_free_work, HZ);
+	}
+	data = df->data;
+	kref_get(&data->kref);
+	mutex_unlock(&df->lock);
+
+	rc = simple_read_from_buffer(buf, size, ppos, data->buf, data->size);
+	kref_put(&data->kref, hypfs_dbfs_data_free);
+	return rc;
+}
+
+static const struct file_operations dbfs_ops = {
+	.read		= dbfs_read,
+	.llseek		= no_llseek,
+};
+
+int hypfs_dbfs_create_file(struct hypfs_dbfs_file *df)
+{
+	df->dentry = debugfs_create_file(df->name, 0400, dbfs_dir, df,
+					 &dbfs_ops);
+	if (IS_ERR(df->dentry))
+		return PTR_ERR(df->dentry);
+	mutex_init(&df->lock);
+	INIT_DELAYED_WORK(&df->data_free_work, data_free_delayed);
+	return 0;
+}
+
+void hypfs_dbfs_remove_file(struct hypfs_dbfs_file *df)
+{
+	debugfs_remove(df->dentry);
+}
+
+int hypfs_dbfs_init(void)
+{
+	dbfs_dir = debugfs_create_dir("s390_hypfs", NULL);
+	if (IS_ERR(dbfs_dir))
+		return PTR_ERR(dbfs_dir);
+	return 0;
+}
+
+void hypfs_dbfs_exit(void)
+{
+	debugfs_remove(dbfs_dir);
+}