From: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
To: jakub@redhat.com
Cc: schwab@suse.de, drepper@redhat.com, libc-hacker@sources.redhat.com
Subject: Re: [PATCH] xdr_array and calloc security fix
Date: Fri, 02 Aug 2002 04:57:00 -0000 [thread overview]
Message-ID: <20020802115729.25576.qmail@md.dent.med.uni-muenchen.de> (raw)
In-Reply-To: <20020802134512.D20867@sunsite.ms.mff.cuni.cz> (message from Jakub Jelinek on Fri, 2 Aug 2002 13:45:12 +0200)
> > But (a > a * b || b > a * b) should work, shouldn't it?
>
> No. For a=1 b=2 this will give the correct answer (no overflow), but
> for a=0x6000000 b=64 it will give incorrect one (no overflow, while
> 0x180000000LL certainly doesn't fit into 32-bits (but 0x80000000 is
> still bigger than any of the operands).
Ok, if we're going to have two comparisions anyway, I'd suggest we
assume at least 32bits and use
a >= 46340 || b >= 46340
(46340 <= sqrt(2^31), if I did my math correctly)
Of course this will detect some cases as overflow which actually
aren't, but that is harmless.
Regards,
Wolfram.
next prev parent reply other threads:[~2002-08-02 11:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-08-01 15:46 Jakub Jelinek
2002-08-02 0:20 ` Ulrich Drepper
2002-08-02 2:29 ` Wolfram Gloger
2002-08-02 2:43 ` Ulrich Drepper
2002-08-02 2:50 ` Ulrich Drepper
2002-08-02 2:56 ` Jakub Jelinek
2002-08-02 4:07 ` Andreas Schwab
2002-08-02 4:46 ` Jakub Jelinek
2002-08-02 4:57 ` Wolfram Gloger [this message]
2002-08-02 5:05 ` Jakub Jelinek
2002-08-02 5:13 ` Wolfram Gloger
2002-08-03 5:03 ` [PATCH] optimize calloc Jakub Jelinek
2002-08-03 12:02 ` Ulrich Drepper
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