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From: Rich Felker <>
To: jvoisin <>
Cc:, James Raphael Tiovalen <>
Subject: Re: [musl] [PATCH v2] Add a safe dequeue integrity check for mallocng
Date: Sat, 16 Sep 2023 12:11:39 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sat, Sep 16, 2023 at 04:58:45PM +0200, jvoisin wrote:
> On 16/09/2023 09:08, James Raphael Tiovalen wrote:
> > This commit adds an integrity check to allow for safer dequeuing of the
> > out-of-band meta structs in mallocng. If the unlikely condition is true
> > due to some sort of heap metadata corruption, we abort.
> Since asserts aren't present in production code[1], I don't think that
> this change is useful.

Did you read the previous (v1 patch) thread or the code? In mallocng,
assert expands to a lightweight assertion check.

> > This approach is similar to the safe unlinking check performed by glibc.
> The metadata in musl's heap implementation are stored out-of-bound.
> Should an attacker be able to locate and modify them, it's already game
> over. Adding a `m->prev->next == m && m->next->prev == m` would only
> impede attackers if they only have an arbitrary read and a one-shot
> arbitrary write that can only overwrite one `meta` instead. This seems
> pretty contrived (as in "unlikely) to me. Do you have any particular
> scenario in mind?
> 1.

Indeed, I'm still mildly unsure of the usefulness of this check, but
not really opposed to it unless it turns out to be costly. (Note: many
of the others already there *are* moderately costly, but are based on
very plausible attack models where the data being checked is easily
reachable via application bugs.) Has anyone checked if this measurably
affects performance?


      reply	other threads:[~2023-09-16 16:11 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-16  7:08 James Raphael Tiovalen
2023-09-16 14:58 ` jvoisin
2023-09-16 16:11   ` Rich Felker [this message]

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