Re: [PATCH v9 2/3] mm: add a field to store names for private anonymous memory

[Suren Baghdasaryan <surenb@google.com>]

On Fri, Sep 3, 2021 at 3:28 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Sep 03, 2021 at 02:56:21PM -0700, Suren Baghdasaryan wrote:
> > On Fri, Sep 3, 2021 at 2:47 PM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > (Sorry, a few more things jumped out at me when I looked again...)
> > >
> > > On Thu, Sep 02, 2021 at 04:18:12PM -0700, Suren Baghdasaryan wrote:
> > > > [...]
> > > > diff --git a/kernel/sys.c b/kernel/sys.c
> > > > index 72c7639e3c98..25118902a376 100644
> > > > --- a/kernel/sys.c
> > > > +++ b/kernel/sys.c
> > > > @@ -2299,6 +2299,64 @@ int __weak arch_prctl_spec_ctrl_set(struct task_struct *t, unsigned long which,
> > > >
> > > >  #define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE)
> > > >
> > > > +#ifdef CONFIG_MMU
> > > > +
> > > > +#define ANON_VMA_NAME_MAX_LEN        256
> > > > +
> > > > +static inline bool is_valid_name_char(char ch)
> > > > +{
> > > > +     /* printable ascii characters, except [ \ ] */
> > > > +     return (ch > 0x1f && ch < 0x5b) || (ch > 0x5d && ch < 0x7f);
> > > > +}
> > >
> > > In the back of my mind, I feel like disallowing backtick would be nice,
> > > but then if $, (, and ) are allowed, it doesn't matter, and that seems
> > > too limiting. :)
> >
> > It's not used by the only current user (Android) and we can always
> > allow more chars later. However going the other direction and
> > disallowing some of them I think would be harder (need to make sure
> > nobody uses them). WDYT if we keep it stricter and relax if needed?
>
> I'd say, if we can also drop each of: ` $ ( )
> then let's do it. Better to keep the obvious shell meta-characters out
> of this, although I don't feel strongly about it. Anything that might
> get confused by this would be similarly confused by binary names too:
>
> $ cat /proc/3407216/maps
> 560bdafd4000-560bdafd6000 r--p 00000000 fd:02 2621909 /tmp/yay`wat
>
> And it's probably easier to change a binary name than to call prctl. :P
>
> I'm good either way. What you have now is great, but if we wanted to be
> extra extra strict, we can add the other 4 above.

While testing v10 I found one case when () are used in the name
"dalvik-main space (region space)". So I can add ` and $ to the
restricted set but not ( and ). Kees, would you be happy with:

static inline bool is_valid_name_char(char ch)
{
    return ch > 0x1f && ch < 0x7f && !strchr("\\`$[]", ch);
}

?

>
> --
> Kees Cook