Re: [RFC][PATCH] Prevent overriding of Symbols in the Kernel, avoiding Undefined behaviour

[Rusty Russell <rusty@rustcorp.com.au>]

On Mon, 2005-12-12 at 18:09 +0530, Ashutosh Naik wrote:
> diff -Naurp linux-2.6.15-rc5-vanilla/kernel/module.c linux-2.6.15-rc5-mod/kernel/module.c
> --- linux-2.6.15-rc5-vanilla/kernel/module.c    2005-12-07 19:32:23.000000000 +0530
> +++ linux-2.6.15-rc5-mod/kernel/module.c        2005-12-12 17:47:28.000000000 +0530
> @@ -1204,6 +1204,63 @@ void *__symbol_get(const char *symbol)
>  }
>  EXPORT_SYMBOL_GPL(__symbol_get);
>  
> +/*
> + * Ensure that an exported symbol [global namespace] does not already exist
> + * in the Kernel or in some other modules exported symbol table.
> + */
> +static int verify_export_symbols(Elf_Shdr *sechdrs,
> +                           const char *strtab,
> +                           struct module *mod)
> +{
> +       struct kernel_symbol *exportsym, *gplsym;
> +       unsigned long i,ret=0,value=0;
> +       struct module *owner;
> +       const unsigned long *crc;
> +       unsigned long index=0;
> +        
> +       spin_lock_irq(&modlist_lock);
> +
> +       exportsym = (struct kernel_symbol *)mod->syms;
> +       gplsym = (struct kernel_symbol *)mod->gpl_syms;
> +
> +       if (exportsym)
> +               for (i = 0; i < mod->num_syms; exportsym++,i++) {

Hi,
	The check for exportsym not being NULL is redundant, since
mod->num_syms will be 0 in that case.  The cast is also redundant.  You
have two identical failure cases at the bottom.  And your use of index
is convoluted: do it after relocations.

How about something like:

	const struct kernel_symbol *sym;
	unsigned int i;
	const unsigned long *crc;
	struct module *owner;

	spin_lock_irq(&modlist_lock);
	for (i = 0; i < mod->num_syms; i++)
		if (__find_symbol(mod->syms[i].name, &owner, &crc, 1))
			goto dup;
	for (i = 0; i < num->num_gpl_syms; i++)
		if (__find_symbol(mod->gpl_syms[i].name,&owner,&crc,1))
			goto dup;
	spin_unlock_irq(&modlist_lock);
	return 0;
dup:
	printk("%s: exports duplicate symbol (owned by %s)\n",
		mod->name, module_name(owner));
	return -ENOEXEC;
}

Cheers,
Rusty.
-- 
 ccontrol: http://ozlabs.org/~rusty/ccontrol

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