[GIT PULL] Usernamespace related locked mount fixes
Eric W. Biederman
ebiederm at xmission.com
Thu Apr 16 23:40:44 UTC 2015
Please pull the for-linus branch from the git tree:
HEAD: e0c9c0afd2fc958ffa34b697972721d81df8a56f mnt: Update detach_mounts to leave mounts connected
Way back in October Andrey Vagin reported that umount(MNT_DETACH) could
be used to defeat MNT_LOCKED. As I worked to fix this I discovered
that combined with mount propagation and an appropriate selection of
shared subtrees a reference to a directory on an unmounted filesystem is
That MNT_DETACH is allowed in user namespace in a form that can break
MNT_LOCKED comes from my early misunderstanding what MNT_DETACH does.
To avoid breaking existing userspace the conflict between MNT_DETACH and
MNT_LOCKED is fixed by leaving mounts that are locked to their parents
in the mount hash table until the last reference goes away.
While investigating this issue I also found an issue with
__detach_mounts. The code was unnecessarily and incorrectly triggering
mount propagation. Resulting in too many mounts going away when a
directory is deleted, and too many cpu cycles are burned while doing
Looking some more I realized that __detach_mounts by only keeping mounts
connected that were MNT_LOCKED it had the potential to still leak
information so I tweaked the code to keep everything locked together
that possibly could be.
This code was almost ready last cycle but Al invented fs_pin which
slightly simplifies this code but required rewrites and retesting,
and I have not been in top form for a while so it took me a while to get
all of that done. Similiarly this pull request is late because I have
been feeling absolutely miserable all week.
The issue of being able to escape a bind mount has not yet been
addressed, as the fixes are not yet mature.
Eric W. Biederman (15):
mnt: Use hlist_move_list in namespace_unlock
mnt: Improve the umount_tree flags
mnt: Don't propagate umounts in __detach_mounts
mnt: In umount_tree reuse mnt_list instead of mnt_hash
mnt: Add MNT_UMOUNT flag
mnt: Delay removal from the mount hash.
mnt: On an unmount propagate clearing of MNT_LOCKED
mnt: Don't propagate unmounts to locked mounts
mnt: Fail collect_mounts when applied to unmounted mounts
mnt: Factor out unhash_mnt from detach_mnt and umount_tree
mnt: Factor umount_mnt from umount_tree
fs_pin: Allow for the possibility that m_list or s_list go unused.
mnt: Honor MNT_LOCKED when detaching mounts
mnt: Fix the error check in __detach_mounts
mnt: Update detach_mounts to leave mounts connected
fs/fs_pin.c | 4 +-
fs/namespace.c | 142 +++++++++++++++++++++++++++++++++----------------
fs/pnode.c | 60 ++++++++++++++++++---
fs/pnode.h | 7 ++-
include/linux/fs_pin.h | 2 +
include/linux/mount.h | 1 +
6 files changed, 159 insertions(+), 57 deletions(-)
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