vdisk_nullio: Add "read_zero" attribute

Add an attribute called "read_zero" to vdisk_nullio devices that
controls whether or not READs from a vdisk_nullio device return
zeroed data buffers.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>



git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@5539 d57e44dd-8a1f-0410-8b47-8ef2f437770f

scst/README

@@ -982,7 +982,7 @@ Intended to be used for performance measurements at the same way as
 blocksize, read_only, removable, tst. See vdisk_fileio above for
 description of those parameters.
 
-vdisk_nullio also has extra attribute:
+vdisk_nullio devices have the following two additional attributes:
 
  - dummy - if this flag is set, LUNs corresponding to this device will
    not appear at the initiator side. This is because SCST will set the
@@ -991,6 +991,13 @@ vdisk_nullio also has extra attribute:
    See also SPC-4 for more information. It is designed to be used as a
    "dummy" placeholder on LUN 0, if LUN 0 is not desired.
 
+ - read_zero - if this flag is set, reading from a vdisk_nullio device
+   returns a buffer filled with byte 0x00. If this flag is cleared
+   (which is the default behavior), the buffer returned to the
+   initiator is not cleared. Although this results in slightly faster
+   operation this is a security hole since any data that is present in
+   kernel memory can be returned to the initiator.
+
 Handler vcdrom allows emulation of a virtual CDROM device using an ISO
 file as backend. It has only single parameter: tst.
 

scst/README_in-tree

@@ -840,7 +840,7 @@ Intended to be used for performance measurements at the same way as
 blocksize, read_only, removable, tst. See vdisk_fileio above for
 description of those parameters.
 
-vdisk_nullio also has extra attribute:
+vdisk_nullio devices have the following two additional attributes:
 
  - dummy - if this flag is set, LUNs corresponding to this device will
    not appear at the initiator side. This is because SCST will set the
@@ -849,6 +849,13 @@ vdisk_nullio also has extra attribute:
    See also SPC-4 for more information. It is designed to be used as a
    "dummy" placeholder on LUN 0, if LUN 0 is not desired.
 
+ - read_zero - if this flag is set, reading from a vdisk_nullio device
+   returns a buffer filled with byte 0x00. If this flag is cleared
+   (which is the default behavior), the buffer returned to the
+   initiator is not cleared. Although this results in slightly faster
+   operation this is a security hole since any data that is present in
+   kernel memory can be returned to the initiator.
+
 Handler vcdrom allows emulation of a virtual CDROM device using an ISO
 file as backend. It has only single parameter: tst.
 

scst/src/dev_handlers/scst_vdisk.c

@@ -109,6 +109,7 @@ static struct scst_trace_log vdisk_local_trace_tbl[] = {
 #define DEF_NV_CACHE			0
 #define DEF_O_DIRECT			0
 #define DEF_DUMMY			0
+#define DEF_READ_ZERO			0
 #define DEF_REMOVABLE			0
 #define DEF_ROTATIONAL			1
 #define DEF_THIN_PROVISIONED		0
@@ -160,6 +161,7 @@ struct scst_vdisk_dev {
 	unsigned int blockio:1;
 	unsigned int cdrom_empty:1;
 	unsigned int dummy:1;
+	unsigned int read_zero:1;
 	unsigned int removable:1;
 	unsigned int thin_provisioned:1;
 	unsigned int thin_provisioned_manually_set:1;
@@ -263,7 +265,8 @@ static int vcdrom_parse(struct scst_cmd *);
 static int non_fileio_parse(struct scst_cmd *);
 static int vdisk_exec(struct scst_cmd *cmd);
 static int vcdrom_exec(struct scst_cmd *cmd);
-static int non_fileio_exec(struct scst_cmd *cmd);
+static int blockio_exec(struct scst_cmd *cmd);
+static int nullio_exec(struct scst_cmd *cmd);
 static void fileio_on_free_cmd(struct scst_cmd *cmd);
 static enum compl_status_e nullio_exec_read(struct vdisk_cmd_params *p);
 static enum compl_status_e blockio_exec_read(struct vdisk_cmd_params *p);
@@ -349,6 +352,10 @@ static ssize_t vdisk_sysfs_o_direct_show(struct kobject *kobj,
 	struct kobj_attribute *attr, char *buf);
 static ssize_t vdev_sysfs_dummy_show(struct kobject *kobj,
 	struct kobj_attribute *attr, char *buf);
+static ssize_t vdev_sysfs_rz_show(struct kobject *kobj,
+	struct kobj_attribute *attr, char *buf);
+static ssize_t vdev_sysfs_rz_store(struct kobject *kobj,
+	struct kobj_attribute *attr, const char *buf, size_t count);
 static ssize_t vdisk_sysfs_removable_show(struct kobject *kobj,
 	struct kobj_attribute *attr, char *buf);
 static ssize_t vdev_sysfs_filename_show(struct kobject *kobj,
@@ -421,6 +428,9 @@ static struct kobj_attribute vdisk_o_direct_attr =
 	__ATTR(o_direct, S_IRUGO, vdisk_sysfs_o_direct_show, NULL);
 static struct kobj_attribute vdev_dummy_attr =
 	__ATTR(dummy, S_IRUGO, vdev_sysfs_dummy_show, NULL);
+static struct kobj_attribute vdev_read_zero_attr =
+	__ATTR(read_zero, S_IWUSR|S_IRUGO, vdev_sysfs_rz_show,
+	       vdev_sysfs_rz_store);
 static struct kobj_attribute vdisk_removable_attr =
 	__ATTR(removable, S_IRUGO, vdisk_sysfs_removable_show, NULL);
 static struct kobj_attribute vdisk_filename_attr =
@@ -516,6 +526,7 @@ static const struct attribute *vdisk_nullio_attrs[] = {
 	&vdisk_rd_only_attr.attr,
 	&vdisk_tst_attr.attr,
 	&vdev_dummy_attr.attr,
+	&vdev_read_zero_attr.attr,
 	&vdisk_removable_attr.attr,
 	&vdev_t10_vend_id_attr.attr,
 	&vdev_vend_specific_id_attr.attr,
@@ -634,7 +645,7 @@ static struct scst_dev_type vdisk_blk_devtype = {
 	.attach_tgt =		vdisk_attach_tgt,
 	.detach_tgt =		vdisk_detach_tgt,
 	.parse =		non_fileio_parse,
-	.exec =			non_fileio_exec,
+	.exec =			blockio_exec,
 	.task_mgmt_fn_done =	vdisk_task_mgmt_fn_done,
 	.get_supported_opcodes = vdisk_get_supported_opcodes,
 	.devt_priv =		(void *)blockio_ops,
@@ -677,7 +688,7 @@ static struct scst_dev_type vdisk_null_devtype = {
 	.attach_tgt =		vdisk_attach_tgt,
 	.detach_tgt =		vdisk_detach_tgt,
 	.parse =		non_fileio_parse,
-	.exec =			non_fileio_exec,
+	.exec =			nullio_exec,
 	.task_mgmt_fn_done =	vdisk_task_mgmt_fn_done,
 	.devt_priv =		(void *)nullio_ops,
 	.get_supported_opcodes = vdisk_get_supported_opcodes,
@@ -2847,8 +2858,7 @@ out:
 	return;
 }
 
-/* blockio and nullio */
-static int non_fileio_exec(struct scst_cmd *cmd)
+static int blockio_exec(struct scst_cmd *cmd)
 {
 	struct scst_vdisk_dev *virt_dev = cmd->dev->dh_priv;
 	const vdisk_op_fn *ops = virt_dev->vdev_devt->devt_priv;
@@ -2875,6 +2885,31 @@ err:
 	goto out;
 }
 
+static int nullio_exec(struct scst_cmd *cmd)
+{
+	struct scst_device *dev = cmd->dev;
+	struct scst_vdisk_dev *virt_dev = dev->dh_priv;
+
+	if (unlikely(virt_dev->read_zero &&
+		     (cmd->data_direction == SCST_DATA_READ ||
+		      cmd->data_direction == SCST_DATA_BIDI))) {
+		struct scatterlist *sge;
+		int i;
+		void *p;
+
+		for_each_sg(cmd->sg, sge, cmd->sg_cnt, i) {
+			p = kmap(sg_page(sge));
+			if (sge->offset == 0 && sge->length == PAGE_SIZE)
+				clear_page(p);
+			else
+				memset(p + sge->offset, 0, sge->length);
+			kunmap(p);
+		}
+	}
+
+	return blockio_exec(cmd);
+}
+
 static int vcdrom_exec(struct scst_cmd *cmd)
 {
 	int res = SCST_EXEC_COMPLETED;
@@ -5942,6 +5977,7 @@ static int vdev_create(struct scst_dev_type *devt,
 
 	virt_dev->rd_only = DEF_RD_ONLY;
 	virt_dev->dummy = DEF_DUMMY;
+	virt_dev->read_zero = DEF_READ_ZERO;
 	virt_dev->removable = DEF_REMOVABLE;
 	virt_dev->rotational = DEF_ROTATIONAL;
 	virt_dev->thin_provisioned = DEF_THIN_PROVISIONED;
@@ -7012,6 +7048,51 @@ static ssize_t vdev_sysfs_dummy_show(struct kobject *kobj,
 		 virt_dev->dummy != DEF_DUMMY ? SCST_SYSFS_KEY_MARK "\n" : "");
 }
 
+static ssize_t vdev_sysfs_rz_show(struct kobject *kobj,
+				  struct kobj_attribute *attr, char *buf)
+{
+	struct scst_device *dev = container_of(kobj, struct scst_device,
+					       dev_kobj);
+	struct scst_vdisk_dev *virt_dev = dev->dh_priv;
+	bool read_zero = virt_dev->read_zero;
+
+	return sprintf(buf, "%d\n%s", read_zero, read_zero != DEF_READ_ZERO ?
+		       SCST_SYSFS_KEY_MARK "\n" : "");
+}
+
+static ssize_t vdev_sysfs_rz_store(struct kobject *kobj,
+				   struct kobj_attribute *attr, const char *buf,
+				   size_t count)
+{
+	struct scst_device *dev = container_of(kobj, struct scst_device,
+					       dev_kobj);
+	struct scst_vdisk_dev *virt_dev = dev->dh_priv;
+	long read_zero;
+	int res;
+	char ch[16];
+
+	sprintf(ch, "%.*s", min_t(int, sizeof(ch) - 1, count), buf);
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 39)
+	res = kstrtol(ch, 0, &read_zero);
+#else
+	res = strict_strtol(ch, 0, &read_zero);
+#endif
+	if (res)
+		goto out;
+	res = -EINVAL;
+	if (read_zero != 0 && read_zero != 1)
+		goto out;
+
+	spin_lock(&virt_dev->flags_lock);
+	virt_dev->read_zero = read_zero;
+	spin_unlock(&virt_dev->flags_lock);
+
+	res = count;
+
+out:
+	return res;
+}
+
 static ssize_t vdisk_sysfs_removable_show(struct kobject *kobj,
 	struct kobj_attribute *attr, char *buf)
 {