Re: [PATCH v3 2/2] blk-zoned: allow BLKREPORTZONE without CAP_SYS_ADMIN

From: Niklas Cassel <redacted>

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: 3ed05a987e0f ("blk-zoned: implement ioctls")
Signed-off-by: Niklas Cassel <redacted>
Cc: stable@vger.kernel.org # v4.10+
---
Changes since v2:
-Drop the FMODE_READ check. Right now it is possible to open() the device with
O_WRONLY and get the zone report from that fd. Therefore adding a FMODE_READ
check on BLKREPORTZONE would break existing applications. Instead, just remove
the existing CAP_SYS_ADMIN check.

  block/blk-zoned.c | 3 ---
  1 file changed, 3 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 0789e6e9f7db..457eceabed2e 100644
--- a/block/blk-zoned.c
+++ b/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;