[RFC] block: relax permission for Persistent Reservations ioctl

[Jingbo Xu <jefflexu@linux.alibaba.com>]

When the shared storage is accessed from containers [1], it's not
recommended to grant CAP_SYS_ADMIN to containers for access to
Persistent Reservations in risk of container escape.

Remove the extra CAP_SYS_ADMIN permission constraint for Persistent
Reservations ioctl which shall do no harm [2].

[1] https://lore.kernel.org/linux-block/345a7cdc-e55b-7aaa-43d4-59b3f911ef18@linux.alibaba.com/
[2] https://lore.kernel.org/linux-block/ZGxaxnOeadVwb2gR@infradead.org/

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
---
I also noticed that the extra CAP_SYS_ADMIN permission constraint is not
added until v4 [*] of original pull request for Persistent Reservation
API.

[*] https://lore.kernel.org/all/1444911052-9423-1-git-send-email-hch@lst.de/
---
 block/ioctl.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index 9c5f637ff153..46c9ac43bbf8 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -260,8 +260,6 @@ static int blkdev_pr_register(struct block_device *bdev,
 	const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
 	struct pr_registration reg;
 
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
 	if (!ops || !ops->pr_register)
 		return -EOPNOTSUPP;
 	if (copy_from_user(&reg, arg, sizeof(reg)))
@@ -278,8 +276,6 @@ static int blkdev_pr_reserve(struct block_device *bdev,
 	const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
 	struct pr_reservation rsv;
 
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
 	if (!ops || !ops->pr_reserve)
 		return -EOPNOTSUPP;
 	if (copy_from_user(&rsv, arg, sizeof(rsv)))
@@ -296,8 +292,6 @@ static int blkdev_pr_release(struct block_device *bdev,
 	const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
 	struct pr_reservation rsv;
 
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
 	if (!ops || !ops->pr_release)
 		return -EOPNOTSUPP;
 	if (copy_from_user(&rsv, arg, sizeof(rsv)))
@@ -314,8 +308,6 @@ static int blkdev_pr_preempt(struct block_device *bdev,
 	const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
 	struct pr_preempt p;
 
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
 	if (!ops || !ops->pr_preempt)
 		return -EOPNOTSUPP;
 	if (copy_from_user(&p, arg, sizeof(p)))
@@ -332,8 +324,6 @@ static int blkdev_pr_clear(struct block_device *bdev,
 	const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
 	struct pr_clear c;
 
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
 	if (!ops || !ops->pr_clear)
 		return -EOPNOTSUPP;
 	if (copy_from_user(&c, arg, sizeof(c)))
-- 
2.19.1.6.gb485710b