Messages in this thread | | | Subject | Re: [PATCH] Fix Warnining in arch/x86/kernel/signal.c | From | Subrata Modak <> | Date | Mon, 18 May 2009 12:08:12 +0530 |
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On Mon, 2009-05-18 at 12:36 +0900, Hiroshi Shimamoto wrote: > Subrata Modak wrote: > > On Fri, 2009-05-15 at 12:32 +0900, Hiroshi Shimamoto wrote: > >> 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? > > > > Oops. No, the compiler does not complain here. It simply compiles fine. > > > > So, do you want to take a different view for the patch against > > arch/x86/kernel/signal.c, or, i would resend it with the following > > things fixed: > > If you don't think this fix is urgent, could you please check whether > that warning is false positive on 32bit or gcc for 64bit has an issue > not to complain against ia32 part? >
I will try to find out.
> I think arch/x86/kernel/signal.c and arch/x86/ia32/ia32_signal.c should > have the same code.
Sure. Not a problem. Please drop the patch for the time being.
Regards-- Subrata
> > Thanks, > Hiroshi
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