[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>

5 files changed, 143 insertions, 60 deletions

diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index 4d2df2f76ea0..475e603fc584 100644
--- a/drivers/s390/block/dasd.c
+++ b/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
diff --git a/drivers/s390/block/dasd_devmap.c b/drivers/s390/block/dasd_devmap.c
index 42e1bf35f689..d71511c7850a 100644
--- a/drivers/s390/block/dasd_devmap.c
+++ b/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
  */
diff --git a/drivers/s390/block/dasd_genhd.c b/drivers/s390/block/dasd_genhd.c
index 5505bc07e1e7..19a1ff03d65e 100644
--- a/drivers/s390/block/dasd_genhd.c
+++ b/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);
diff --git a/drivers/s390/block/dasd_int.h b/drivers/s390/block/dasd_int.h
index df9f6999411d..d1e4f2c1264c 100644
--- a/drivers/s390/block/dasd_int.h
+++ b/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 *);
 
diff --git a/drivers/s390/block/dasd_ioctl.c b/drivers/s390/block/dasd_ioctl.c
index 26075e95b1ba..72261e4c516d 100644
--- a/drivers/s390/block/dasd_ioctl.c
+++ b/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;
 }