On Thu, Aug 22, 2013 at 01:54:15PM -0700, Linus Torvalds wrote:
> On Thu, Aug 22, 2013 at 1:48 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> >
> > Sure. But aren't they always last?
>
> What do you mean? I'd say that the /proc lookup is always *innermost*.
> Which means that it certainly cannot bail out, since there are many
> levels of nesting outside of it.
>
> > With the current code structure, trying to enforce some kind of
> > security restriction in the middle of lookup seems really unpleasant.
>
> If it's conditional (ie "linkat behaves differently from openat"), it
> certainly means that we'd have to pass in that info in annoying ways.
Nope. All we need to pass is one more LOOKUP_... Add
if (unlikely(nd->last_type == LAST_BIND)) {
if ((nd->flags & LOOKUP_BLAH) && !may_flink(...)) {
terminate_walk(nd);
return -EINVAL;
}
}
in the beginning of lookup_last() and pass LOOKUP_BLAH in flags when
linkat() calls user_path_at(). That will affect *only* the terminal
symlinks and cost nothing in all normal cases. The same check can
bloody well go into path_init() - take
if (*name) {
if (!can_lookup(dentry->d_inode)) {
fdput(f);
return -ENOTDIR;
}
}
in there and slap
else {
if ((flags & LOOKUP_BLAH) && !may_flink(...)) {
fdput(f);
return -EINVAL;
}
}
after it.
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