Re: [PATCH] Fix Warnining in arch/x86/kernel/signal.c

[Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>]

Subrata Modak wrote:
> Hello Hiroshi-san,
> 
> On Thu, 2009-05-14 at 09:24 +0900, Hiroshi Shimamoto wrote:
> H. Peter Anvin wrote:
>>> Ingo Molnar wrote:
>>>>>>>  
>>>>>>>         if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
>>>>>>>                 goto badframe;
>>>>>>> -       if (__get_user(set.sig[0], &frame->sc.oldmask) || (_NSIG_WORDS > 1
>>>>>>> -               && __copy_from_user(&set.sig[1], &frame->extramask,
>>>>>>> -                                   sizeof(frame->extramask))))
>>>>>>> +
>>>>>>> +        if ( (__copy_from_user(&set.sig[1], &frame->extramask,
>>>>>>> +                sizeof(frame->extramask)) && _NSIG_WORDS > 1) || 
>>>>>>> +                __get_user(set.sig[0], &frame->sc.oldmask))
>>>>>>>                 goto badframe;
>>>>>> I'm not sure why this eliminates that warning.
>>>>>> set.sig[0] may not be initialized too, if __copy_from_user() failed.
>>>>> True, but only when either or both of __copy_from_user() and
>>>>> (_NSIG_WORDS > 1) fails. But in all instances set.sig[1] gets
>>>>> initialized.
>>>>>
>>>>>> I don't have enough time to look at this right now, sorry.
>>>>>>
>>>>>> Another question, __copy_from_user() will be called even if
>>>>>> _NSIG_WORDS is less than 2, perhaps it never occurs.
>>>>>> I think, to check _NSIG_WORDS > 1 before calling __copy_from_user()
>>>>>> is better.
>>>>> Fine. Let Ingo/Thomas/Peter decide whether they would like this fix or
>>>>> drop it.
>>>> If you get the Acked-by from Hiroshi-san it looks good to me. He 
>>>> modified this code last.
>>>>
>>> This seriously looks wrong to me.  If _NSIG_WORDS == 1, then calling
>>> __copy_from_user here is a serious error.
>> Right. If _NSIG_WORDS is 1, sigset_t set has only sig[0], writing to
>> set.sig[1] means stack corruption.
>>
>> Subrata, could you try like this?
>> if ((_NSIG_WORDS > 1 && __copy_from_user(&set.sig[1], ...) ||
>>       __get_user(set.sig[0], ...))
>>
>>
> 
> How about now ? Thanks for pointing that out. My mistake ;-)

Hi Subrata, I have a question.
Have you tried to compile on x86_64 whether the compiler claims the
similar code in sys32_sigreturn() in arch/x86/ia32/ia32_signal.c?

Thanks,
Hiroshi