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From: "guillaume at morinfr dot org" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug malloc/20646] sysmalloc incorrectly fails with custom morecore
 function
Date: Wed, 14 Jul 2021 12:29:42 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D20646

--- Comment #9 from Guillaume Morin <guillaume at morinfr dot org> ---
That is not an equivalent solution though. What you're effectively saying n=
ow
that all libhugetlbfs users need to find, test and validate an entire malloc
implementation that suits them to use hugetlb (i.e we can't use glibc's mal=
loc
and we can't use libhugetblfs). Or are you expecting all existing users to
write their own custom malloc implementation?

You're mentioning hooking in morecore() is a security hazard. But from a
security point of view, wouldn't it just as good to support morecore()
interposition instead of the entire malloc implementation? And this would g=
ive
current users a rather easy fix and a documented interface (unless I am mis=
sing
anything).

I must say I find your other point about being subtly broken is a little ha=
rd
to digest. I put together a reproducer and a simple fix for this issue almo=
st 5
years ago... Yes, things will be broken if nothing is done to fix them :-)=
=20

Though this is the only issue with morecore() that I know of (and can only =
be
reached if the morecore implementation allows trimming). Keep in mind that
there are a lot of libhugetlbfs users and all of them are using morecore().
We've been using libhugetblfs in production for a long time (10+ years) wit=
hout
any issues.=20

Are there some unfixable issues with the morecore() scheme that we never
encountered besides the (understandable) security concerns?

--=20
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