This patchset adds support for keeping mount ownership information in
the kernel, and allow unprivileged mount(2) and umount(2) in certain
cases.
This can be useful for the following reasons:
- mount(8) can store ownership ("user=XY" option) in the kernel
instead, or in addition to storing it in /etc/mtab. For example if
private namespaces are used with mount propagations /etc/mtab
becomes unworkable, but using /proc/mounts works fine
- fuse won't need a special suid-root mount/umount utility. Plain
umount(8) can easily be made to work with unprivileged fuse mounts
- users can use bind mounts without having to pre-configure them in
/etc/fstab
All this is done in a secure way, and unprivileged bind and fuse
mounts are disabled by default and can be enabled through sysctl or
/proc/sys.
One thing that is missing from this series is the ability to restrict
user mounts to private namespaces. The reason is that private
namespaces have still not gained the momentum and support needed for
painless user experience. So such a feature would not yet get enough
attention and testing. However adding such an optional restriction
can be done with minimal changes in the future, once private
namespaces have matured.
An earlier version of these patches have been discussed here:
http://lkml.org/lkml/2005/5/3/64
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