[Bug 695259] Re: btrfs tree balance can be triggered by non-root user

[Gary M]

Emailed to linux-btrfs by  Ben Hutchings.  Submitted to linux-kernel:
git pull request for 2.6.38-rc1.

** Bug watch added: Email to linux-btrfs at vger #
   mailto:linux-btrfs at vger.kernel.org

** Also affects: linux via
   mailto:linux-btrfs at vger.kernel.org
   Importance: Undecided
       Status: New

** Changed in: linux
       Status: New => Fix Released

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Title:
  btrfs tree balance can be triggered by non-root user

Status in The Linux Kernel:
  Fix Released
Status in “btrfs-tools” package in Ubuntu:
  Invalid
Status in “linux” package in Ubuntu:
  Fix Released
Status in “linux-2.6” package in Debian:
  Fix Released

Bug description:
  Balance tree action of btrfs command should be limited to only root
  user, because it may cause data corrupt and usually result in an
  uninterruptible process which is causing a heavy I/O load (the process
  may keep runing for a long time because the action is not a easy
  deal).

  Run the following command as a non-root user will also start the balance tree action ( / is btrfs here, with ext4 /boot):
  $ btrfs filesystem balance /

  I think this problem will cause serious issues if somebody uses it in
  a production system (though it is really not recommended).

  What's more, I'm not sure whether this should be a bug in the Linux kernel/btrfs-tools, because such action is actually performed by using system calls. If I try to make a snapshot in a directory by a user who does not have the access, it will generate an error like this:
  $ pwd
  /home
  $ whoami
  aron
  $ btrfs subvolume snapshot . backhome
  Create a snapshot of '.' in './backhome'
  ERROR: cannot snapshot '.

  I think at least a workaround is needed to be settled in btrfs-tools
  (geteuid test) before the kernel side has this problem fixed.

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