From: Andreas Schwab <schwab@linux-m68k.org>
To: Siddhesh Poyarekar <siddhesh@gotplt.org>
Cc: libc-alpha@sourceware.org, fweimer@redhat.com, carlos@redhat.com
Subject: Re: [RFC] Supporting malloc_usable_size
Date: Fri, 02 Dec 2022 13:03:14 +0100 [thread overview]
Message-ID: <87sfhyrp19.fsf@igel.home> (raw)
In-Reply-To: <20221124213258.305192-1-siddhesh@gotplt.org> (Siddhesh Poyarekar's message of "Thu, 24 Nov 2022 16:32:58 -0500")
On Nov 24 2022, Siddhesh Poyarekar wrote:
> This is in context of this systemd issue:
>
> https://github.com/systemd/systemd/issues/22801
>
> through which I had discovered that systemd was (ab)using
> malloc_usable_size to use spare space in an allocated object. This was
> discovered when _FORTIFY_SOURCE=3 flagged this as a buffer overflow,
> since the compiler is unable to see that the space beyond the allocation
> was safe to use.
Which it isn't. Nothing prevents malloc to hand out the extra space to
a different thread any time, so the size returned by malloc_usable_size
can get outdated instantly.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
"And now for something completely different."
next prev parent reply other threads:[~2022-12-02 12:03 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-24 21:32 [RFC] Supporting malloc_usable_size Siddhesh Poyarekar
2022-12-02 4:42 ` DJ Delorie via Libc-alpha
2022-12-02 5:00 ` Sam James via Libc-alpha
2022-12-02 5:28 ` DJ Delorie via Libc-alpha
2022-12-02 12:36 ` Siddhesh Poyarekar
2022-12-02 19:16 ` DJ Delorie via Libc-alpha
2022-12-02 19:49 ` Siddhesh Poyarekar
2022-12-02 19:57 ` DJ Delorie via Libc-alpha
2022-12-02 12:03 ` Andreas Schwab [this message]
2022-12-02 12:22 ` Siddhesh Poyarekar
2022-12-02 12:34 ` Andreas Schwab
2022-12-02 12:39 ` Florian Weimer via Libc-alpha
2022-12-05 18:46 ` Zack Weinberg via Libc-alpha
2022-12-05 19:04 ` Siddhesh Poyarekar
2022-12-05 20:35 ` Florian Weimer via Libc-alpha
2022-12-06 19:25 ` Siddhesh Poyarekar
2022-12-07 10:01 ` Florian Weimer via Libc-alpha
2022-12-07 16:34 ` Siddhesh Poyarekar
2022-12-07 16:54 ` Adhemerval Zanella Netto via Libc-alpha
2022-12-07 16:57 ` Sam James via Libc-alpha
2022-12-07 17:39 ` Florian Weimer via Libc-alpha
2022-12-09 15:42 ` Siddhesh Poyarekar
2022-12-07 18:45 ` DJ Delorie via Libc-alpha
2022-12-02 12:54 ` Florian Weimer via Libc-alpha
-- strict thread matches above, loose matches on Subject: below --
2022-12-02 13:54 Wilco Dijkstra via Libc-alpha
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