Public bug reported:

SRU Justification

Impact: Stéphane reported regression for btrfs workloads employing shiftfs.
Unprivileged users can already toggle whether a subvolume will be ro or
rw. This is broken on current shiftfs as we haven't whitelisted these
ioctls().

Fix: To enable this with shiftfs we need to whitelist BTRFS_IOC_FS_INFO,
BTRFS_IOC_SUBVOL_GETFLAGS, BTRFS_IOC_SUBVOL_SETFLAGS. All of them should
be safe for unprivileged users.

Regression Potential: Limited to shiftfs.

Test Case: Tested with LXD running shiftfs on top of btrfs and verified
btrfs subvolumes can be made ro or rw.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1832316

Title:
  shiftfs: allow changing ro/rw for subvolumes

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