On 10/04/2013 05:41:25 PM, Eric W. Biederman wrote:
This patchset is an attempt to address two problems:
1) Not all modifications to the filesystems happen through the vfs and
since the vfs can not cope with a mount point being unlinked or
renamed filesystems whose modifications that do not come through
the
vfs are required to lie.
2) Through an oversight it is now possible for one unprivileged user
to
mount something on another unprivileged users dentry and make it
impossible for the other user to unlink or rename that dentry.
It is now technically possible to easily lift the restriction on
unlinking and renaming files with mount points on them, with a
corresponding reduction in complexity of the vfs semantics and a small
code side reduction.
A todo item I've had _forever_ is fixing chroot() to not be broken so
that you can trivially break out of a chroot via:
chdir("/");
mkdir("sub");
chroot("sub");
chdir("./../../../../../../../..");
(Because chroot() affects where "/" points but NOT where "." points to,
and chdir does an == check with the dentry "/" points at to know when
to stop, so if you move "/" under "." you can back up to the actual
root of the tree.)
The above is why lxc uses pivot_root() instead of chroot().
These days, we have multiple mount trees so there's no reason chroot()
can't trim the process local mount tree (creating a new bind mount if
necessary). Except my todo list runneth over and I haven't had a chance
to dig in and see what would be involved. (Last time I brought this up
people were wondering why chroot() didn't just move "." to the new "/"
if it wasn't under it. I had no idea, still don't.)
Rob--
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