public inbox for libc-alpha@sourceware.org
 help / color / mirror / Atom feed
From: Florian Weimer <fweimer@redhat.com>
To: up201407890@alunos.dcc.fc.up.pt, Martin Sebor <msebor@redhat.com>
Cc: libc-alpha@sourceware.org
Subject: Re: use-after-free / double-free exploit mitigation
Date: Thu, 07 Sep 2017 16:00:00 -0000	[thread overview]
Message-ID: <8feaa5bc-94f7-547c-c241-a82c41bd7472@redhat.com> (raw)
In-Reply-To: <20170906144653.14363oywmmoc9ug4@webmail.alunos.dcc.fc.up.pt>

On 09/06/2017 02:46 PM, up201407890@alunos.dcc.fc.up.pt wrote:
> What are your thoughts on adding a SAFE_FREE() macro to glibc:
> 
> #define SAFE_FREE(x) do { if((x) != 0x0) { free(x); (x) = (void *)0x1; }
> } while(0)
> 
> After free(x), we set x to an address that will crash when dereferenced
> (use-after-free), and will also crash when it's an argument to free().
> Note that NULL isn't used, because free(NULL) does nothing, which might
> hide potential double-free bugs.

Maybe GCC should optionally do this for the actual call to free.  There
is some debate to what extend pointer *values* remain valid after free.
Martin Sebor may have some thought on that.

In any case, some GCC assistance is needed so that

  free (some_struct->ptr);
  free (some_struct);

actually clobbers some_struct->ptr.  I don't think we want to call out
to explicit_bzero here.

Thanks,
Florian

  reply	other threads:[~2017-09-07 16:00 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-06 12:47 up201407890
2017-09-07 16:00 ` Florian Weimer [this message]
2017-09-08 12:45   ` Martin Sebor
2017-09-09 17:59 Federico Manuel Bento
2017-09-10 15:41 ` Martin Sebor
2017-09-11 15:36   ` Federico Manuel Bento

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=8feaa5bc-94f7-547c-c241-a82c41bd7472@redhat.com \
    --to=fweimer@redhat.com \
    --cc=libc-alpha@sourceware.org \
    --cc=msebor@redhat.com \
    --cc=up201407890@alunos.dcc.fc.up.pt \
    /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).