blk-zoned: allow BLKREPORTZONE without CAP_SYS_ADMIN

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 <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: Aravind Ramesh <[email protected]>
Reviewed-by: Adam Manzanares <[email protected]>
Reviewed-by: Himanshu Madhani <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>
Cc: [email protected] # v4.10+
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Niklas Cassel

block/blk-zoned.c

@@ -360,9 +360,6 @@ 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;