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

[Jamie Lokier <jamie@shareable.org>]

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