From: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
To: libc-hacker@sources.redhat.com
Subject: Re: [PATCH] xdr_array and calloc security fix
Date: Fri, 02 Aug 2002 02:29:00 -0000 [thread overview]
Message-ID: <20020802092945.24679.qmail@md.dent.med.uni-muenchen.de> (raw)
In-Reply-To: <20020802004635.Y20867@sunsite.ms.mff.cuni.cz> (message from Jakub Jelinek on Fri, 2 Aug 2002 00:46:35 +0200)
Hi,
> + /* size_t is unsigned so the behavior on overflow is defined. */
> + bytes = n * elem_size;
> + if (bytes / elem_size != n) {
> + MALLOC_FAILURE_ACTION;
> + return 0;
> + }
This is of course correct, but some (long) time ago I've measured that
the cost for the division is quite noticeable, for say, the very
common calloc(1, small_size).
I've given up on being able to do this fast _and_ portably.
Do we already have some system-specific mechanism to detect the rare
overflow case for a 32bit-multiplication without having to perform a
division?
Regards,
Wolfram.
next prev parent reply other threads:[~2002-08-02 9:29 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20020802092945.24679.qmail@md.dent.med.uni-muenchen.de \
--to=wmglo@dent.med.uni-muenchen.de \
--cc=libc-hacker@sources.redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).