linux-kernel - Re: [PATCH v5 12/37] lib: prevent module unloading if memory is not freed

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Message-ID: <CAJuCfpFDY=+gmVytYY6iCYds5OW0gVfwrXguWWq0B0G1qq7hYQ@mail.gmail.com>
Date: Tue, 12 Mar 2024 11:41:28 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Luis Chamberlain <mcgrof@...nel.org>
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Subject: Re: [PATCH v5 12/37] lib: prevent module unloading if memory is not freed

On Tue, Mar 12, 2024 at 11:22 AM Luis Chamberlain <mcgrof@...nel.org> wrote:
>
> On Wed, Mar 06, 2024 at 10:24:10AM -0800, Suren Baghdasaryan wrote:
> > Skip freeing module's data section if there are non-zero allocation tags
> > because otherwise, once these allocations are freed, the access to their
> > code tag would cause UAF.
>
> So you just let them linger?

Well, I think this is not a normal situation when a module allocated
some memory and then is being unloaded without freeing that memory,
no?

>
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
>
>
> >  /* Free a module, remove from lists, etc. */
> >  static void free_module(struct module *mod)
> >  {
> > +     bool unload_codetags;
> > +
> >       trace_module_free(mod);
> >
> > -     codetag_unload_module(mod);
> > +     unload_codetags = codetag_unload_module(mod);
> > +     if (!unload_codetags)
> > +             pr_warn("%s: memory allocation(s) from the module still alive, cannot unload cleanly\n",
> > +                     mod->name);
> > +
>
> Because this is not unwinding anything. Should'd we check if we can
> free all tags first, if we can't then we can't free the module. If we
> can then ensure we don't enter a state where we can't later?

unload_codetags already indicates that someone has a live reference to
one or more tags of that module, so we can't free them. Maybe I
misunderstood your suggestion?

>
>   Luis