linux-kernel - Re: [PATCH v2 1/7] modules: Create rlimit for module space

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Message-ID: <CAG48ez0pPX7XNqSj4dVG1s+PaDBCh4ar5xw1WcY1sLBPV_QAzA@mail.gmail.com>
Date:   Fri, 12 Oct 2018 20:23:15 +0200
From:   Jann Horn <jannh@...gle.com>
To:     rick.p.edgecombe@...el.com
Cc:     Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, jeyu@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-mips@...ux-mips.org, linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-arch <linux-arch@...r.kernel.org>, kristen@...ux.intel.com,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        deneen.t.dock@...el.com
Subject: Re: [PATCH v2 1/7] modules: Create rlimit for module space

On Fri, Oct 12, 2018 at 2:35 AM Jann Horn <jannh@...gle.com> wrote:
> On Fri, Oct 12, 2018 at 1:40 AM Rick Edgecombe
> <rick.p.edgecombe@...el.com> wrote:
> > This introduces a new rlimit, RLIMIT_MODSPACE, which limits the amount of
> > module space a user can use. The intention is to be able to limit module space
> > allocations that may come from un-privlidged users inserting e/BPF filters.
>
> Note that in some configurations (iirc e.g. the default Ubuntu
> config), normal users can use the subuid mechanism (the /etc/subuid
> config file and the /usr/bin/newuidmap setuid helper) to gain access
> to 65536 UIDs, which means that in such a configuration,
> RLIMIT_MODSPACE*65537 is the actual limit for one user. (Same thing
> applies to RLIMIT_MEMLOCK.)

Actually, I may have misremembered, perhaps it's not installed by
default - I just checked in a Ubuntu VM, and the newuidmap helper from
the uidmap package wasn't installed.