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

["H. Peter Anvin" <hpa@zytor.com>]

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.

	-hpa