[S390] dasd: fix race between open and offline

The dasd_open function uses the private_data pointer of the gendisk to
find the dasd_block structure that matches the gendisk. When a DASD
device is set offline, we set the private_data pointer of the gendisk
to NULL and later remove the dasd_block structure, but there is still
a small race window, in which dasd_open could first read a pointer
from the private_data field and then try to use it, after the structure
has already been freed.
To close this race window, we will store a pointer to the dasd_devmap
structure of the base device in the private_data field. The devmap
entries are not deleted, and we already have proper locking and
reference counting in place, so that we can safely get from a devmap
pointer to the dasd_device and dasd_block structures of the device.

Signed-off-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/block/dasd.c

@@ -2314,15 +2314,14 @@ static void dasd_flush_request_queue(struct dasd_block *block)
 
 static int dasd_open(struct block_device *bdev, fmode_t mode)
 {
-	struct dasd_block *block = bdev->bd_disk->private_data;
 	struct dasd_device *base;
 	int rc;
 
-	if (!block)
+	base = dasd_device_from_gendisk(bdev->bd_disk);
+	if (!base)
 		return -ENODEV;
 
-	base = block->base;
-	atomic_inc(&block->open_count);
+	atomic_inc(&base->block->open_count);
 	if (test_bit(DASD_FLAG_OFFLINE, &base->flags)) {
 		rc = -ENODEV;
 		goto unlock;
@@ -2355,21 +2354,28 @@ static int dasd_open(struct block_device *bdev, fmode_t mode)
 		goto out;
 	}
 
+	dasd_put_device(base);
 	return 0;
 
 out:
 	module_put(base->discipline->owner);
 unlock:
-	atomic_dec(&block->open_count);
+	atomic_dec(&base->block->open_count);
+	dasd_put_device(base);
 	return rc;
 }
 
 static int dasd_release(struct gendisk *disk, fmode_t mode)
 {
-	struct dasd_block *block = disk->private_data;
+	struct dasd_device *base;
 
-	atomic_dec(&block->open_count);
-	module_put(block->base->discipline->owner);
+	base = dasd_device_from_gendisk(disk);
+	if (!base)
+		return -ENODEV;
+
+	atomic_dec(&base->block->open_count);
+	module_put(base->discipline->owner);
+	dasd_put_device(base);
 	return 0;
 }
 
@@ -2378,20 +2384,20 @@ static int dasd_release(struct gendisk *disk, fmode_t mode)
  */
 static int dasd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
 {
-	struct dasd_block *block;
 	struct dasd_device *base;
 
-	block = bdev->bd_disk->private_data;
-	if (!block)
+	base = dasd_device_from_gendisk(bdev->bd_disk);
+	if (!base)
 		return -ENODEV;
-	base = block->base;
 
 	if (!base->discipline ||
-	    !base->discipline->fill_geometry)
+	    !base->discipline->fill_geometry) {
+		dasd_put_device(base);
 		return -EINVAL;
-
-	base->discipline->fill_geometry(block, geo);
-	geo->start = get_start_sect(bdev) >> block->s2b_shift;
+	}
+	base->discipline->fill_geometry(base->block, geo);
+	geo->start = get_start_sect(bdev) >> base->block->s2b_shift;
+	dasd_put_device(base);
 	return 0;
 }
 
@@ -2528,7 +2534,6 @@ void dasd_generic_remove(struct ccw_device *cdev)
 	dasd_set_target_state(device, DASD_STATE_NEW);
 	/* dasd_delete_device destroys the device reference. */
 	block = device->block;
-	device->block = NULL;
 	dasd_delete_device(device);
 	/*
 	 * life cycle of block is bound to device, so delete it after
@@ -2650,7 +2655,6 @@ int dasd_generic_set_offline(struct ccw_device *cdev)
 	dasd_set_target_state(device, DASD_STATE_NEW);
 	/* dasd_delete_device destroys the device reference. */
 	block = device->block;
-	device->block = NULL;
 	dasd_delete_device(device);
 	/*
 	 * life cycle of block is bound to device, so delete it after

drivers/s390/block/dasd_devmap.c

@@ -674,6 +674,36 @@ dasd_device_from_cdev(struct ccw_device *cdev)
 	return device;
 }
 
+void dasd_add_link_to_gendisk(struct gendisk *gdp, struct dasd_device *device)
+{
+	struct dasd_devmap *devmap;
+
+	devmap = dasd_find_busid(dev_name(&device->cdev->dev));
+	if (IS_ERR(devmap))
+		return;
+	spin_lock(&dasd_devmap_lock);
+	gdp->private_data = devmap;
+	spin_unlock(&dasd_devmap_lock);
+}
+
+struct dasd_device *dasd_device_from_gendisk(struct gendisk *gdp)
+{
+	struct dasd_device *device;
+	struct dasd_devmap *devmap;
+
+	if (!gdp->private_data)
+		return NULL;
+	device = NULL;
+	spin_lock(&dasd_devmap_lock);
+	devmap = gdp->private_data;
+	if (devmap && devmap->device) {
+		device = devmap->device;
+		dasd_get_device(device);
+	}
+	spin_unlock(&dasd_devmap_lock);
+	return device;
+}
+
 /*
  * SECTION: files in sysfs
  */

drivers/s390/block/dasd_genhd.c

@@ -73,7 +73,7 @@ int dasd_gendisk_alloc(struct dasd_block *block)
 	if (base->features & DASD_FEATURE_READONLY ||
 	    test_bit(DASD_FLAG_DEVICE_RO, &base->flags))
 		set_disk_ro(gdp, 1);
-	gdp->private_data = block;
+	dasd_add_link_to_gendisk(gdp, base);
 	gdp->queue = block->request_queue;
 	block->gdp = gdp;
 	set_capacity(block->gdp, 0);

drivers/s390/block/dasd_int.h

@@ -686,6 +686,9 @@ struct dasd_device *dasd_device_from_cdev(struct ccw_device *);
 struct dasd_device *dasd_device_from_cdev_locked(struct ccw_device *);
 struct dasd_device *dasd_device_from_devindex(int);
 
+void dasd_add_link_to_gendisk(struct gendisk *, struct dasd_device *);
+struct dasd_device *dasd_device_from_gendisk(struct gendisk *);
+
 int dasd_parse(void);
 int dasd_busid_known(const char *);
 

drivers/s390/block/dasd_ioctl.c

@@ -42,16 +42,22 @@ dasd_ioctl_api_version(void __user *argp)
 static int
 dasd_ioctl_enable(struct block_device *bdev)
 {
-	struct dasd_block *block = bdev->bd_disk->private_data;
+	struct dasd_device *base;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
-	dasd_enable_device(block->base);
+	base = dasd_device_from_gendisk(bdev->bd_disk);
+	if (!base)
+		return -ENODEV;
+
+	dasd_enable_device(base);
 	/* Formatting the dasd device can change the capacity. */
 	mutex_lock(&bdev->bd_mutex);
-	i_size_write(bdev->bd_inode, (loff_t)get_capacity(block->gdp) << 9);
+	i_size_write(bdev->bd_inode,
+		     (loff_t)get_capacity(base->block->gdp) << 9);
 	mutex_unlock(&bdev->bd_mutex);
+	dasd_put_device(base);
 	return 0;
 }
 
@@ -62,11 +68,14 @@ dasd_ioctl_enable(struct block_device *bdev)
 static int
 dasd_ioctl_disable(struct block_device *bdev)
 {
-	struct dasd_block *block = bdev->bd_disk->private_data;
+	struct dasd_device *base;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
+	base = dasd_device_from_gendisk(bdev->bd_disk);
+	if (!base)
+		return -ENODEV;
 	/*
 	 * Man this is sick. We don't do a real disable but only downgrade
 	 * the device to DASD_STATE_BASIC. The reason is that dasdfmt uses
@@ -75,7 +84,7 @@ dasd_ioctl_disable(struct block_device *bdev)
 	 * using the BIODASDFMT ioctl. Therefore the correct state for the
 	 * device is DASD_STATE_BASIC that allows to do basic i/o.
 	 */
-	dasd_set_target_state(block->base, DASD_STATE_BASIC);
+	dasd_set_target_state(base, DASD_STATE_BASIC);
 	/*
 	 * Set i_size to zero, since read, write, etc. check against this
 	 * value.
@@ -83,6 +92,7 @@ dasd_ioctl_disable(struct block_device *bdev)
 	mutex_lock(&bdev->bd_mutex);
 	i_size_write(bdev->bd_inode, 0);
 	mutex_unlock(&bdev->bd_mutex);
+	dasd_put_device(base);
 	return 0;
 }
 
@@ -191,26 +201,36 @@ static int dasd_format(struct dasd_block *block, struct format_data_t *fdata)
 static int
 dasd_ioctl_format(struct block_device *bdev, void __user *argp)
 {
-	struct dasd_block *block = bdev->bd_disk->private_data;
+	struct dasd_device *base;
 	struct format_data_t fdata;
+	int rc;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 	if (!argp)
 		return -EINVAL;
-
-	if (block->base->features & DASD_FEATURE_READONLY ||
-	    test_bit(DASD_FLAG_DEVICE_RO, &block->base->flags))
+	base = dasd_device_from_gendisk(bdev->bd_disk);
+	if (!base)
+		return -ENODEV;
+	if (base->features & DASD_FEATURE_READONLY ||
+	    test_bit(DASD_FLAG_DEVICE_RO, &base->flags)) {
+		dasd_put_device(base);
 		return -EROFS;
-	if (copy_from_user(&fdata, argp, sizeof(struct format_data_t)))
+	}
+	if (copy_from_user(&fdata, argp, sizeof(struct format_data_t))) {
+		dasd_put_device(base);
 		return -EFAULT;
+	}
 	if (bdev != bdev->bd_contains) {
 		pr_warning("%s: The specified DASD is a partition and cannot "
 			   "be formatted\n",
-			   dev_name(&block->base->cdev->dev));
+			   dev_name(&base->cdev->dev));
+		dasd_put_device(base);
 		return -EINVAL;
 	}
-	return dasd_format(block, &fdata);
+	rc = dasd_format(base->block, &fdata);
+	dasd_put_device(base);
+	return rc;
 }
 
 #ifdef CONFIG_DASD_PROFILE
@@ -340,8 +360,8 @@ static int dasd_ioctl_information(struct dasd_block *block,
 static int
 dasd_ioctl_set_ro(struct block_device *bdev, void __user *argp)
 {
-	struct dasd_block *block =  bdev->bd_disk->private_data;
-	int intval;
+	struct dasd_device *base;
+	int intval, rc;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
@@ -350,10 +370,17 @@ dasd_ioctl_set_ro(struct block_device *bdev, void __user *argp)
 		return -EINVAL;
 	if (get_user(intval, (int __user *)argp))
 		return -EFAULT;
-	if (!intval && test_bit(DASD_FLAG_DEVICE_RO, &block->base->flags))
+	base = dasd_device_from_gendisk(bdev->bd_disk);
+	if (!base)
+		return -ENODEV;
+	if (!intval && test_bit(DASD_FLAG_DEVICE_RO, &base->flags)) {
+		dasd_put_device(base);
 		return -EROFS;
+	}
 	set_disk_ro(bdev->bd_disk, intval);
-	return dasd_set_feature(block->base->cdev, DASD_FEATURE_READONLY, intval);
+	rc = dasd_set_feature(base->cdev, DASD_FEATURE_READONLY, intval);
+	dasd_put_device(base);
+	return rc;
 }
 
 static int dasd_ioctl_readall_cmb(struct dasd_block *block, unsigned int cmd,
@@ -372,59 +399,78 @@ static int dasd_ioctl_readall_cmb(struct dasd_block *block, unsigned int cmd,
 int dasd_ioctl(struct block_device *bdev, fmode_t mode,
 	       unsigned int cmd, unsigned long arg)
 {
-	struct dasd_block *block = bdev->bd_disk->private_data;
+	struct dasd_block *block;
+	struct dasd_device *base;
 	void __user *argp;
+	int rc;
 
 	if (is_compat_task())
 		argp = compat_ptr(arg);
 	else
 		argp = (void __user *)arg;
 
-	if (!block)
-                return -ENODEV;
-
 	if ((_IOC_DIR(cmd) != _IOC_NONE) && !arg) {
 		PRINT_DEBUG("empty data ptr");
 		return -EINVAL;
 	}
 
+	base = dasd_device_from_gendisk(bdev->bd_disk);
+	if (!base)
+		return -ENODEV;
+	block = base->block;
+	rc = 0;
 	switch (cmd) {
 	case BIODASDDISABLE:
-		return dasd_ioctl_disable(bdev);
+		rc = dasd_ioctl_disable(bdev);
+		break;
 	case BIODASDENABLE:
-		return dasd_ioctl_enable(bdev);
+		rc = dasd_ioctl_enable(bdev);
+		break;
 	case BIODASDQUIESCE:
-		return dasd_ioctl_quiesce(block);
+		rc = dasd_ioctl_quiesce(block);
+		break;
 	case BIODASDRESUME:
-		return dasd_ioctl_resume(block);
+		rc = dasd_ioctl_resume(block);
+		break;
 	case BIODASDFMT:
-		return dasd_ioctl_format(bdev, argp);
+		rc = dasd_ioctl_format(bdev, argp);
+		break;
 	case BIODASDINFO:
-		return dasd_ioctl_information(block, cmd, argp);
+		rc = dasd_ioctl_information(block, cmd, argp);
+		break;
 	case BIODASDINFO2:
-		return dasd_ioctl_information(block, cmd, argp);
+		rc = dasd_ioctl_information(block, cmd, argp);
+		break;
 	case BIODASDPRRD:
-		return dasd_ioctl_read_profile(block, argp);
+		rc = dasd_ioctl_read_profile(block, argp);
+		break;
 	case BIODASDPRRST:
-		return dasd_ioctl_reset_profile(block);
+		rc = dasd_ioctl_reset_profile(block);
+		break;
 	case BLKROSET:
-		return dasd_ioctl_set_ro(bdev, argp);
+		rc = dasd_ioctl_set_ro(bdev, argp);
+		break;
 	case DASDAPIVER:
-		return dasd_ioctl_api_version(argp);
+		rc = dasd_ioctl_api_version(argp);
+		break;
 	case BIODASDCMFENABLE:
-		return enable_cmf(block->base->cdev);
+		rc = enable_cmf(base->cdev);
+		break;
 	case BIODASDCMFDISABLE:
-		return disable_cmf(block->base->cdev);
+		rc = disable_cmf(base->cdev);
+		break;
 	case BIODASDREADALLCMB:
-		return dasd_ioctl_readall_cmb(block, cmd, argp);
+		rc = dasd_ioctl_readall_cmb(block, cmd, argp);
+		break;
 	default:
 		/* if the discipline has an ioctl method try it. */
-		if (block->base->discipline->ioctl) {
-			int rval = block->base->discipline->ioctl(block, cmd, argp);
-			if (rval != -ENOIOCTLCMD)
-				return rval;
-		}
-
-		return -EINVAL;
+		if (base->discipline->ioctl) {
+			rc = base->discipline->ioctl(block, cmd, argp);
+			if (rc == -ENOIOCTLCMD)
+				rc = -EINVAL;
+		} else
+			rc = -EINVAL;
 	}
+	dasd_put_device(base);
+	return rc;
 }