The block layer generic blk_revalidate_disk_zones() checks the validity of
zone descriptors reported by a disk using the blk_revalidate_zone_cb()
callback function executed for each zone descriptor. If a ZBC disk reports
invalid zone descriptors, blk_revalidate_disk_zones() returns an error and
sd_zbc_read_zones() changes the disk capacity to 0, which in turn results
in the gendisk structure capacity to be set to 0. This all works well for
the first revalidate pass on a disk and the block layer detects the
capactiy change.

On the second revalidate pass, blk_revalidate_disk_zones() is called again
and sd_zbc_report_zones() executed to check the zones a second time.
However, for this second pass, the gendisk capacity is now 0, which results
in sd_zbc_report_zones() to do nothing and to report success and no
zones. blk_revalidate_disk_zones() in turn returns success and sets the
disk queue chunk_sectors limit with zero as no zones were checked, causing
a oops to trigger on the BUG_ON(!is_power_of_2(chunk_sectors)) in
blk_queue_chunk_sectors().

Fix this by using the sdkp capacity field rather than the gendisk capacity
for the report zones loop in sd_zbc_report_zones(). Also add a check to
return immediately an error if the sdkp capacity is 0.  With this fix,
invalid/buggy ZBC disk scan does not trigger a oops and are exposed with a
0 capacity. This change also preserve the chance for the disk to be
correctly revalidated on the second revalidate pass as the scsi disk
structure capacity field is always set to the disk reported value when
sd_zbc_report_zones() is called.

Link: https://lore.kernel.org/r/20200219063800.880834-1-damien.lemoal@wdc.com
Fixes: d4100351 ("block: rework zone reporting")
Cc: Cc: <stable@vger.kernel.org> # v5.5
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>