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Message-ID: <20130128211706.GA10654@openwall.com>
Date: Tue, 29 Jan 2013 01:17:06 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: dmg2john
On Tue, Jan 29, 2013 at 01:09:01AM +0400, Solar Designer wrote:
> 5. As also spotted by Milen:
>
> <@gat3way> @jmgosney @jeremiahg @DhiruKholia @solardiz Hm I think I found the problem....cno = ceil(header2.datasize / 4096.0) - 2; cno is int
>
> We must not do any floating-point math. When header2.datasize is large,
> there may be precision loss here, and the resulting value may be other
> than what we expect. We should express this without resorting to
> floating-point intermediate values:
>
> cno = (header2.datasize + 4095) / 4096 - 2;
>
> Milen - is this what you meant, too?
Oh, there's more to it. We do:
cno = ceil(header2.datasize / 4096.0) - 2;
chunk = (unsigned char *) malloc(header2.datasize);
data_size = header2.datasize - cno * 4096;
and we have a nice undefined signed integer overflow in "cno * 4096" and
when assigning to data_size.
These int's should probably be declared size_t instead.
Alexander
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