ftp.delorie.com/archives/browse.cgi   search  
Mail Archives: djgpp/2019/06/17/17:48:35

X-Authentication-Warning: delorie.com: mail set sender to djgpp-bounces using -f
From: =?UTF-8?Q?Hans-Bernhard_Br=c3=b6ker?= <HBBroeker AT t-online DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: malloc() returns pointer to already allocated memory
Date: Mon, 17 Jun 2019 23:31:08 +0200
Lines: 30
Message-ID: <gmqf52F2te7U1@mid.dfncis.de>
References: <158e5d20-0a90-4beb-de48-da328379d8fb AT gmail DOT com>
Mime-Version: 1.0
X-Trace: news.dfncis.de hKxyORMsNafl1zPem6f9NAJfd1NFy6xt5ulzAiB0kAsbmGFGiXQAXnTd7n
Cancel-Lock: sha1:pu/75Ocj1u2YYzxxs3dg1A3lf8I=
Openpgp: preference=signencrypt
Autocrypt: addr=HBBroeker AT t-online DOT de; keydata=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User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
Thunderbird/60.7.1
In-Reply-To: <158e5d20-0a90-4beb-de48-da328379d8fb@gmail.com>
Bytes: 5895
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
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

Am 17.06.2019 um 02:27 schrieb J.W. Jagersma [via djgpp AT delorie DOT com]:
> I ran into this issue with malloc(). It seems that, given enough
> allocations, malloc() will eventually return a pointer into already
> allocated memory.

The problem with that claim is that it's just not correct.  Your code is
_not_ detecting what you claim it does.  It really detects nothing at all.

malloc() makes no guarantee whatsoever about the contents of the memory
you get --- if you wanted a specific content, you know where to find
calloc(), memset() and friends.

Reading the contents of malloc()ed memory prior to writing to it yields,
at best, indeterminate results.  If done like in your test program
(using pointers to a signed, multi-byte integer data type), is actually
worse: it invokes undefined behaviour.  So any conclusions drawn from
looking at the value delivered by such read-outs, like yours, are
automatically invalid.

Please also keep in mind that this is DJGPP, targeting DOS.  That's a
single-user operating system with no need nor concept of security
whatsoever.  That means there's absolutely no particular reason for any
part of the system, be that the DJGPP libc or run-time itself, the DPMI
host, or the underlying DOS, to support security mechanisms intended to
avoid, e.g., data leakage from one process to the other.

In other words: a DOS DPMI host is well within its rights serving fresh
pages whose contents just so happen to be copies of previously served
ones.  That's not the same as handing out the same page twice, nor does
it constitute, by any stretch of the imagination, clobbering.

- Raw text -


  webmaster     delorie software   privacy  
  Copyright © 2019   by DJ Delorie     Updated Jul 2019