X-Authentication-Warning:	delorie.com: mail set sender to djgpp-bounces using -f
X-Recipient:	djgpp AT delorie DOT com
X-Original-DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=gmail.com; s=20161025;
	h=subject:to:references:from:openpgp:autocrypt:message-id:date
	:user-agent:mime-version:in-reply-to:content-language
	:content-transfer-encoding;
	bh=ojEGYOj3aIrv59fT0L9N2epamUlYRc/M/It96Gg1MiA=;
	b=P6DLDNfO7wMtFt5bHD5tQqedhJ3norhlz2iIltnxg/T4pABsKj9Q61d5sLVWZ2eScD
	NFOTCMLaWTmCYmPD25mEu7bkEVF/rxlgrIdHefW+x25YGy6aAJHLatiEFEMhRGj3SYbZ
	47jF9RQZorhLHA2hnSSM8fTb7MmXubfFeO2r7jtYqqrC5VLyxM4SQ8Jbh4riRF1hryEU
	wFM5j/6N4/qzWbi07webp3xa5UWaytrdANoWuf5wTUTFxT5nt7vhUFuwnfLWG1KmiaHD
	raA3d99+NSABZYBHejsjAArHyJxp82PKAElZ4FHTNkUImin6UmLoEdabTYkLE8LKUFzl
	pAhQ==
X-Google-DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=1e100.net; s=20161025;
	h=x-gm-message-state:subject:to:references:from:openpgp:autocrypt
	:message-id:date:user-agent:mime-version:in-reply-to
	:content-language:content-transfer-encoding;
	bh=ojEGYOj3aIrv59fT0L9N2epamUlYRc/M/It96Gg1MiA=;
	b=boZvJpvrAXXPZSSJw1yR/5PnoOHCRX3Yie0Tk4hS2Obplzq7Y+NylgdLvmVzHsl5U3
	WBFchC462XTwU7kJiT2AdPQP/WnFtJdWHs4GSYkdKUhf3/ixEsQquHfcXf6JRahJ5Gpt
	R8McXmfU0000Sq90gzQKgldjAwS+J7RxJ4+TDCtDRuszj5SQDlceSSY1fHm6tfrCUXgq
	GTht9TmVfa+csF/HR3MieD3FQH6bdTyw9So8nvs/QAOymY/FlPi4o7rcxB7ZHYGAFEqw
	4kKVe+n1olLBYh4RkBzCvJO9cBF1bA92DAOe8JSyku92SMYENiKFwQMQi2snNi6mAkmE
	JTgw==
X-Gm-Message-State:	APjAAAUVuh8dmm+V6vDt3u7BmV7o2bREosF4ReRfLngtdVdSKhYqERTB
	M/Q13iJh6UjMCSW0yXq7tm0VaiSa
X-Google-Smtp-Source:	APXvYqxgCrkhdnAGiYki7veCkxUwqxKYbSHGTJb6q72YyR8hclo+eL4jlFpBYPzhlSnWqfzbbrOsFQ==
X-Received:	by 2002:a17:906:db:: with SMTP id 27mr39362892eji.153.1560789177328;
	Mon, 17 Jun 2019 09:32:57 -0700 (PDT)
Subject:	Re: malloc() returns pointer to already allocated memory
To:	djgpp AT delorie DOT com
References:	<158e5d20-0a90-4beb-de48-da328379d8fb AT gmail DOT com>
	<qe76u1$1kj8$1 AT gioia DOT aioe DOT org>
	<f0b68226-f6f4-244a-6dd5-a8ecbabb584b AT gmail DOT com>
	<qe79eb$1urs$1 AT gioia DOT aioe DOT org>
From:	"J.W. Jagersma (jwjagersma AT gmail DOT com) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
Openpgp:	id=D1694EA4DA1338AF4905293BA5102F469FA45960
Autocrypt:	addr=jwjagersma AT gmail DOT com; prefer-encrypt=mutual; keydata=
	mJMEWlMYlBMJKyQDAwIIAQENBAMEORD9eiW30pI0XzJbuE7/4WF3ZyEOkpRgrmZnpTRmzXMW
	z22N+2YrczEM+q+NzM/wn8XOVH4hZ7eSaUsLT86YLS+gF/F44IbRZVCHxdrL+qSQQ0SafwDM
	Aaddx2azX+6MtlFO2B6oDbCHT7Nn5oQi3IgR+pgBzaCkfxyOnU1wjvO0JEouVy4gSmFnZXJz
	bWEgPGp3amFnZXJzbWFAZ21haWwuY29tPojQBBMTCgA4FiEE0WlOpNoTOK9JBSk7pRAvRp+k
	WWAFAlpTGJQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQpRAvRp+kWWA3xAH/WIBG
	sLngyIrTsn5uKz4JygtlCfjMRRSwl3/UIaW96VvIM/wUyzHl+vlyLmuclOjAiTVia/Js03Ar
	zB9iCHZQ0QH/W8cRwHjRNZRukU2IR8eqoGsl6hTUrrAAOKOVO04wrjO4jGDHg3Sw2GxBx7Md
	mD0QRId/gFwR/1UWS0jBdSUWC7iXBFpTGJQSCSskAwMCCAEBDQQDBFipNF/RUEAer/hhT6yJ
	5no1ZLAZgpypvWZ3xJSrBKmcDTaOmNKNRrw1dNtSZ6M6wYcBmtCq7uvR5iiGyK3nD+olwe7a
	4WDkhEEvbmdAYl2LnBsYeyruoW+N+KiMalvf9SphDmBi2NwdSZ1IhnBpxlUns8jqlgZGvG1G
	xE1sleq7AwEKCYi4BBgTCgAgFiEE0WlOpNoTOK9JBSk7pRAvRp+kWWAFAlpTGJQCGwwACgkQ
	pRAvRp+kWWBnyAH+JLrW/cK2aVDvq2nxn471opBgHyExzMi0hvbuy8BjyEt+AfL0RNCFcdds
	CQakIGDv5k69TAgOftECgASwv6CG5wH8D3jnksh6YvYMf0hCBlSfwJ5ehIeqQTj0m2410RgC
	KWywqmfU1X5YVXgmuXatRNgV/ggXS2Q7GnSP/StQzlh3sQ==
Message-ID:	<e151fcfa-79cc-6512-1b84-821ec70b24ff@gmail.com>
Date:	Mon, 17 Jun 2019 18:31:50 +0200
User-Agent:	Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101
	Thunderbird/60.7.1
MIME-Version:	1.0
In-Reply-To:	<qe79eb$1urs$1@gioia.aioe.org>
Reply-To:	djgpp AT delorie DOT com
Errors-To:	nobody AT delorie DOT com
X-Mailing-List:	djgpp AT delorie DOT com
X-Unsubscribes-To:	listserv AT delorie DOT com

On 2019-06-17 07:48, Rod Pemberton wrote:
> One thing he could do is reduce the likelihood, i.e., probability, that
> he'll get a false positive, i.e., random value.  He could check for
> multiple magic values in a row.  The more values he checks for, the
> lower the probability will be that it's random.  I'd probably
> check for an entire block.
Then the test also depends on how well aligned the pointers returned by 
malloc are. eg. you write a 16-byte value to 0x1000, if malloc next 
returns a pointer to 0x1008 it still overlaps, but this would be more 
difficult to detect.

- Raw text -