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

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Date:	Mon, 22 Oct 2012 20:40:46 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
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 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.)

-Kees

-- 
Kees Cook
Chrome OS Security
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