Re: [PATCH 1/2] fs: add link restrictions

[Kees Cook]

On Sat, Jun 30, 2012 at 2:14 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Jun 25, 2012 at 02:05:26PM -0700, Kees Cook wrote:
>
>> +config PROTECTED_LINKS
>> +     bool "Evaluate vulnerable link conditions"
>> +     default y
>
> Remember Linus' rants about 'default y' in general?

I added these configs due to other people's requests. I am happy to
remove them all and have the sysctls start their life == 1. It would
eliminate all the #ifdef logic too.

>> +     /* Check parent directory mode and owner. */
>
> I suspect that we ought to simply pass that parent directory as argument - caller
> *does* have a reference to it, so we don't need to mess with ->d_lock, etc.

I don't see where the parent is held in either path_openat nor
path_lookupat. What should I be passing into may_follow_link() for the
parent?

>> +                     err = may_follow_link(&link);
>> +                     if (unlikely(err))
>> +                             break;
>
> No.  This is definitely wrong - you are leaking dentries and vfsmount here.

What should I do to avoid the leak? I thought it was avoiding the need
to call put_link because it aborts before calling follow_link.

>> +             error = may_follow_link(&link);
>> +             if (unlikely(error))
>> +                     break;
>
> Ditto.

Same thing here -- it aborts before the follow_link. I must be
misunderstanding something. What am I missing?

Thanks for the feedback! I'll clean up the other things you mentioned as well.

-Kees

-- 
Kees Cook
Chrome OS Security
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/