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

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

[Subrata Modak]

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], ...))
> 
> 

I tried out and the compiler does not complain in this case.
Updated Patch below. Please review.

Signed-Off-By: Subrata Modak <subrata@linux.vnet.ibm.com>
To: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>,
Cc: H. Peter Anvin <hpa@zytor.com>,
Cc: Ingo Molnar <mingo@elte.hu>,
Cc: x86@kernel.org,
Cc: Sachin P Sant <sachinp@linux.vnet.ibm.com>,
Cc: Andi Kleen <andi@firstfloor.org>,
Cc: Andi Kleen <ak@linux.intel.com>,
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>,
Cc: Thomas Gleixner <tglx@linutronix.de>,
Cc: Ingo Molnar <mingo@redhat.com>
Subject: Re:[PATCH] Fix Warnining in arch/x86/kernel/signal.c
---

--- a/arch/x86/kernel/signal.c	2009-05-14 11:27:15.000000000 +0530
+++ b/arch/x86/kernel/signal.c	2009-05-14 11:50:52.000000000 +0530
@@ -576,9 +576,9 @@ unsigned long sys_sigreturn(struct pt_re
 
 	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 ( (_NSIG_WORDS > 1 && __copy_from_user(&set.sig[1],
+               &frame->extramask, sizeof(frame->extramask))) ||
+               __get_user(set.sig[0], &frame->sc.oldmask))
 		goto badframe;
 
 	sigdelsetmask(&set, ~_BLOCKABLE);

---
Regards--
Subrata

> I wonder whether gcc really complains about the case of
> __get_user(set.sig[0], ...) failure.
> Why, the case which sig[0] initialized and sig[1] uninitialized is NG
> and the case which sig[0] uninitialized and sig[1] initialized is OK.
> 
> Thanks,
> Hiroshi

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

[Hiroshi Shimamoto]

Subrata Modak wrote:
> Hello Hiroshi-san,

Hi Subrata,

> 
> 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], ...))
>>
>>
> 
> I tried out and the compiler does not complain in this case.
> Updated Patch below. Please review.

thanks for testing, it looks OK except small nits.
Could you please check with checkpatch.pl?

> 
> Signed-Off-By: Subrata Modak <subrata@linux.vnet.ibm.com>

WARNING: Signed-off-by: is the preferred form

> To: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>,
> Cc: H. Peter Anvin <hpa@zytor.com>,
> Cc: Ingo Molnar <mingo@elte.hu>,
> Cc: x86@kernel.org,
> Cc: Sachin P Sant <sachinp@linux.vnet.ibm.com>,
> Cc: Andi Kleen <andi@firstfloor.org>,
> Cc: Andi Kleen <ak@linux.intel.com>,
> Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
> Cc: Balbir Singh <balbir@linux.vnet.ibm.com>,
> Cc: Thomas Gleixner <tglx@linutronix.de>,
> Cc: Ingo Molnar <mingo@redhat.com>
> Subject: Re:[PATCH] Fix Warnining in arch/x86/kernel/signal.c
> ---
> 
> --- a/arch/x86/kernel/signal.c	2009-05-14 11:27:15.000000000 +0530
> +++ b/arch/x86/kernel/signal.c	2009-05-14 11:50:52.000000000 +0530
> @@ -576,9 +576,9 @@ unsigned long sys_sigreturn(struct pt_re
>  
>  	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 ( (_NSIG_WORDS > 1 && __copy_from_user(&set.sig[1],

ERROR: space prohibited after that open parenthesis '('

> +               &frame->extramask, sizeof(frame->extramask))) ||

ERROR: code indent should use tabs where possible

> +               __get_user(set.sig[0], &frame->sc.oldmask))

ERROR: code indent should use tabs where possible

Thanks,
Hiroshi

>  		goto badframe;
>  
>  	sigdelsetmask(&set, ~_BLOCKABLE);
> 
> ---
> Regards--
> Subrata
> 
>> I wonder whether gcc really complains about the case of
>> __get_user(set.sig[0], ...) failure.
>> Why, the case which sig[0] initialized and sig[1] uninitialized is NG
>> and the case which sig[0] uninitialized and sig[1] initialized is OK.
>>
>> Thanks,
>> Hiroshi
> 

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

[Subrata Modak]

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 ;-)

Signed-off-by: Subrata Modak <subrata@linux.vnet.ibm.com>
To: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>,
Cc: H. Peter Anvin <hpa@zytor.com>,
Cc: Ingo Molnar <mingo@elte.hu>,
Cc: x86@kernel.org,
Cc: Sachin P Sant <sachinp@linux.vnet.ibm.com>,
Cc: Andi Kleen <andi@firstfloor.org>,
Cc: Andi Kleen <ak@linux.intel.com>,
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>,
Cc: Thomas Gleixner <tglx@linutronix.de>,
Cc: Ingo Molnar <mingo@redhat.com>
Subject: Re:[PATCH] Fix Warnining in arch/x86/kernel/signal.c
---

--- a/arch/x86/kernel/signal.c	2009-05-14 11:27:15.000000000 +0530
+++ b/arch/x86/kernel/signal.c	2009-05-14 14:36:24.000000000 +0530
@@ -576,9 +576,9 @@ unsigned long sys_sigreturn(struct pt_re
 
 	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 ((_NSIG_WORDS > 1 && __copy_from_user(&set.sig[1],
+		&frame->extramask, sizeof(frame->extramask))) ||
+		__get_user(set.sig[0], &frame->sc.oldmask))
 		goto badframe;
 
 	sigdelsetmask(&set, ~_BLOCKABLE);

---
Regards--
Subrata

> I wonder whether gcc really complains about the case of
> __get_user(set.sig[0], ...) failure.
> Why, the case which sig[0] initialized and sig[1] uninitialized is NG
> and the case which sig[0] uninitialized and sig[1] initialized is OK.
> 
> Thanks,
> Hiroshi