Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks and file bind mounts (try #5)

Jamie Lokier
2009-11-23T22:49:51Z

Jeff Layton wrote:
> > check_path_accessible seems pretty horrible. If a process is running
> > inside of a subdirectory it doesn't have permissions to access, say
> > a chroot, /proc/self/fd/XXX becomes completely unusable.
> >
>
> Hmm...I have this in there:
>
> + /* are we at global root or root of namespace? */
> + if ((tdentry == root.dentry && vfsmnt == root.mnt) ||
> + vfsmnt->mnt_parent == vfsmnt)
> + break;
>
> ...In the case of a chroot, wouldn't "current->fs->root" point to the
> root of the process' namespace? Or am I misunderstanding what
> current->fs actually represents?

A process can run inside a subdirectory it doesn't have permissions to
access without that being a chroot.

It can also run inside a subdirectory that isn't accessible from it's
root, if that's how it was started - as well as having other
descriptors pointing to things outside its root.

It can also be passed file descriptors from outside it's root while
it's running.

Really, I think the /proc/PID/fd/N check should restrict the open to
the O_* limitations that were used to open fd N before, and not have
any connection to actual paths at the time of this check.

-- Jamie