[PATCH v2] block: check disk exist before trying to add partition

[Yufen Yu <yuyufen@xxxxxxxxxx>]

If disk have been deleted, we should return fail for ioctl
BLKPG_DEL_PARTITION. Otherwise, the directory /sys/class/block
may remain invalid symlinks file. The race as following:

blkdev_open
				del_gendisk
				    disk->flags &= ~GENHD_FL_UP;
				    blk_drop_partitions
blkpg_ioctl
    bdev_add_partition
    add_partition
        device_add
	    device_add_class_symlinks

ioctl may add_partition after del_gendisk() have tried to delete
partitions. Then, symlinks file will be created.

Reviewed-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Yufen Yu <yuyufen@xxxxxxxxxx>
---
 block/partitions/core.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/block/partitions/core.c b/block/partitions/core.c
index 186d4fbd9f09..b123ccb2cf64 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -454,17 +454,26 @@ int bdev_add_partition(struct block_device *bdev, int partno,
 		sector_t start, sector_t length)
 {
 	struct block_device *part;
+	struct gendisk *disk = bdev->bd_disk;
+	int ret;
 
-	mutex_lock(&bdev->bd_disk->open_mutex);
-	if (partition_overlaps(bdev->bd_disk, start, length, -1)) {
-		mutex_unlock(&bdev->bd_disk->open_mutex);
-		return -EBUSY;
+	mutex_lock(&disk->open_mutex);
+	if (!(disk->flags & GENHD_FL_UP)) {
+		ret = -ENXIO;
+		goto out;
+	}
+
+	if (partition_overlaps(disk, start, length, -1)) {
+		ret = -EBUSY;
+		goto out;
 	}
 
-	part = add_partition(bdev->bd_disk, partno, start, length,
+	part = add_partition(disk, partno, start, length,
 			ADDPART_FLAG_NONE, NULL);
-	mutex_unlock(&bdev->bd_disk->open_mutex);
-	return PTR_ERR_OR_ZERO(part);
+	ret = PTR_ERR_OR_ZERO(part);
+out:
+	mutex_unlock(&disk->open_mutex);
+	return ret;
 }
 
 int bdev_del_partition(struct block_device *bdev, int partno)
-- 
2.25.4