Re: [PATCH] In-kernel module loader 1/7

From: Rusty Russell (rusty@rustcorp.com.au)
Date: Thu Sep 19 2002 - 20:22:08 EST

In message <20020919183843.GA16568@kroah.com> you write:
> On Thu, Sep 19, 2002 at 03:54:40PM +0200, Roman Zippel wrote:
> > I already said often enough, a module has only to answer the simple
> > question: Is it safe to unload the module?
>
> And with a LSM module, how can it answer that? There's no way, unless
> we count every time someone calls into our module. And if you do that,
> no one will even want to use your module, given the number of hooks, and
> the paths those hooks are on (the speed hit would be horrible.)

Well, it's up to you. You *could* implement:

#define call_security(method , ...) \
        ({ int __ret; \
           if (try_module_get(security_ops->owner)) { \
                __ret = security_ops->method(__VA_ARGS__); \
                module_put(security_ops->owner); \
           } else \
                /* If unloading or loading, default to "allow" */ \
                __ret = 0; \
          __ret; \
        })

Now, if you don't have CONFIG_MODULES this becomes the code as it is
now. If you don't have CONFIG_MODULE_UNLOAD, this becomes:

        if (security_ops->owner && security_ops->owner->live)
                __ret = security_ops->method(__VA_ARGS__);
        else
                __ret = 0;

With the case of CONFIG_MODULE_UNLOAD, it looks *really* horrible (53
instructions with 6 branches: ewww...). So I would recommend
register_security insert a shim and take the hit itself:

#ifdef CONFIG_MODULE_UNLOAD
        if (ops->owner) {
                module_ops->real = ops;
                ops = module_ops;
        }
#endif

Then module_ops does the inc/dec wrappers (well, it can optimize if
the ops can't sleep...).

Rusty. 

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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This archive was generated by hypermail 2b29 : Mon Sep 23 2002 - 22:00:29 EST