Messages in this thread | | | Date | Thu, 14 May 2009 09:24:12 +0900 | From | Hiroshi Shimamoto <> | Subject | Re: [PATCH] Fix Warnining in arch/x86/kernel/signal.c |
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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 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
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