blk-zoned: allow BLKREPORTZONE without CAP_SYS_ADMIN

commit 4d643b6 upstream.

A user space process should not need the CAP_SYS_ADMIN capability set
in order to perform a BLKREPORTZONE ioctl.

Getting the zone report is required in order to get the write pointer.
Neither read() nor write() requires CAP_SYS_ADMIN, so it is reasonable
that a user space process that can read/write from/to the device, also
can get the write pointer. (Since e.g. writes have to be at the write
pointer.)

Fixes: 3ed05a9 ("blk-zoned: implement ioctls")
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Aravind Ramesh <aravind.ramesh@wdc.com>
Reviewed-by: Adam Manzanares <a.manzanares@samsung.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: stable@vger.kernel.org # v4.10+
Link: https://lore.kernel.org/r/20210811110505.29649-3-Niklas.Cassel@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

block/blk-zoned.c

@@ -288,9 +288,6 @@ int blkdev_report_zones_ioctl(struct block_device *bdev, fmode_t mode,
 	if (!blk_queue_is_zoned(q))
 		return -ENOTTY;
 
-	if (!capable(CAP_SYS_ADMIN))
-		return -EACCES;
-
 	if (copy_from_user(&rep, argp, sizeof(struct blk_zone_report)))
 		return -EFAULT;