linux-kernel - Re: [PATCH 1/4] module: add syscall to load module from fd

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Date:	Tue, 23 Oct 2012 02:08:31 -0200
From:	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
To:	Kees Cook <keescook@...omium.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, mtk.manpages@...il.com,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	jonathon@...masters.org
Subject: Re: [PATCH 1/4] module: add syscall to load module from fd

On Tue, Oct 23, 2012 at 1:40 AM, Kees Cook <keescook@...omium.org> wrote:
> On Mon, Oct 22, 2012 at 7:37 PM, Lucas De Marchi
> <lucas.demarchi@...fusion.mobi> wrote:
>> On Mon, Oct 22, 2012 at 5:39 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>>> "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> writes:
>>>>> FIX: add flags arg to sys_finit_module()
>>>>>
>>>>> Thanks to Michael Kerrisk for keeping us honest.
>>>>
>>>> w00t! Thanks, Rusty ;-).
>>>>
>>>> Acked-by: Michael Kerrisk <mtk.manpages@...il.com>
>>>
>>> Here's the version I ended up with when I added two flags.
>>>
>>> Lucas, is this useful to you?
>>>
>>> BTW Michael: why aren't the syscall man pages in the kernel source?
>>>
>>> Thanks,
>>> Rusty.
>>>
>>> module: add flags arg to sys_finit_module()
>>>
>>> Thanks to Michael Kerrisk for keeping us honest.  These flags are actually
>>> useful for eliminating the only case where kmod has to mangle a module's
>>> internals: for overriding module versioning.
>>>
>>> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
>
> Acked-by: Kees Cook <keescook@...omium.org>
>
>> I wonder if we shouldn't get a new init_module2() as well, adding the
>> flags parameter. Of course this would be in another patch.
>>
>> My worries are that for compressed modules we still need to use
>> init_module() and then --force won't work with signed modules.
>
> For those cases, I think it should remain up to userspace to do the
> decompress and use init_module(). The code I'd written for patching
> module-init-tools basically just kept the fd around if it didn't need
> to mangle the module, and it would use finit_module (written before
> the flags argument was added):
>
>         /* request kernel linkage */
> -       ret = init_module(module->data, module->len, opts);
> +       if (fd < 0)
> +               ret = init_module(module->data, module->len, opts);
> +       else {
> +           ret = finit_module(fd, opts);
> +           if (ret != 0 && errno == ENOSYS)
> +                   ret = init_module(module->data, module->len, opts);
> +       }
>         if (ret != 0) {
>
> (And yes, I realize kmod is what'll actually be getting this logic.
> This was for my testing in Chrome OS, which is still using
> module-init-tools.)

sure... but do you realize this will fail in case kernel is checking
module signature and we passed --force to modprobe (therefore mangled
the decompressed memory area)?


Lucas De Marchi
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