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
next prev parent 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
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