[Bug 917446] [NEW] switch_root does not allow switching to a non-block device as the new root filesytem

[Mickey]

Public bug reported:

The current switch_root does a sanity check to ensure that it does not
wipe out the new root filesystem by checking the device id of the parent
and child directories. If they are the same, then the child directory is
not considered a mount point and the contents are deleted recursively.

This presents a problem because non-block device mounted file systems
such as tmpfs and ramfs both report the same device id from struct stat.
Which is '0'.

So if you have your to-be root filesystem contained in a non-block
device (/proc/filesystems: nodev entries), it will be wiped out before
chroot/execve ever happens.

This can be verified by running stat against the root and to-be root
filesystems in the initramfs.

Releases affected = All
Versions affected = All

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

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https://bugs.launchpad.net/bugs/917446

Title:
  switch_root does not allow switching to a non-block device as the new
  root filesytem

Status in “util-linux” package in Ubuntu:
  New

Bug description:
  The current switch_root does a sanity check to ensure that it does not
  wipe out the new root filesystem by checking the device id of the
  parent and child directories. If they are the same, then the child
  directory is not considered a mount point and the contents are deleted
  recursively.

  This presents a problem because non-block device mounted file systems
  such as tmpfs and ramfs both report the same device id from struct
  stat. Which is '0'.

  So if you have your to-be root filesystem contained in a non-block
  device (/proc/filesystems: nodev entries), it will be wiped out before
  chroot/execve ever happens.

  This can be verified by running stat against the root and to-be root
  filesystems in the initramfs.

  Releases affected = All
  Versions affected = All

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