From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753155AbZENJNK (ORCPT ); Thu, 14 May 2009 05:13:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751917AbZENJMz (ORCPT ); Thu, 14 May 2009 05:12:55 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:44013 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751010AbZENJMy (ORCPT ); Thu, 14 May 2009 05:12:54 -0400 From: Subrata Modak To: Hiroshi Shimamoto Cc: "H. Peter Anvin" , Balbir Singh , Andi Kleen , Ingo Molnar , x86@kernel.org, Linux Kernel , Thomas Gleixner , Sachin P Sant , Subrata Modak , Andi Kleen , Ingo Molnar Date: Thu, 14 May 2009 14:42:47 +0530 Message-Id: <20090514091247.32082.38639.sendpatchset@subratamodak.linux.ibm.com> Subject: Re:[PATCH] Fix Warnining in arch/x86/kernel/signal.c Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 To: Hiroshi Shimamoto , Cc: H. Peter Anvin , Cc: Ingo Molnar , Cc: x86@kernel.org, Cc: Sachin P Sant , Cc: Andi Kleen , Cc: Andi Kleen , Cc: Linux Kernel , Cc: Balbir Singh , Cc: Thomas Gleixner , Cc: Ingo Molnar 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