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Message-ID: <20171002170111.GA6713@gmail.com>
Date: Mon, 2 Oct 2017 10:01:11 -0700
From: Eric Biggers <ebiggers3@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
David Howells <dhowells@...hat.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
Kirill Marinushkin <k.marinushkin@...il.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Ilhan Gurel <ilhan.gurel@...il.com>, security@...nel.org,
stable <stable@...r.kernel.org>
Subject: Re: Modular BIG_KEYS (was: Re: [PATCH v4] security/keys: rewrite all
of big_key crypto)
On Mon, Oct 02, 2017 at 09:14:36AM +0200, Geert Uytterhoeven wrote:
> Now this has hit mainline, the "BIG_KEYS" Kconfig symbol appeared on my
> radar. Is there any reason this cannot be tristate?
>
> The help text says:
>
> This option provides support for holding large keys within the kernel
> (for example Kerberos ticket caches). The data may be stored out to
> swapspace by tmpfs.
>
> If you are unsure as to whether this is required, answer N.
>
> So to save kernel size, I wan't to save N, but for a distro kernel that might
> have Kerberos users, you currently need to say Y, while M would be nicer.
>
> The symbol seems to just control the build of security/keys/big_key.c,
> which could use module_init() in the modular case.
> I'm not sending a patch to change BIG_KEYS from bool to tristate, as this is
> crypto, and I don't understand the full implications.
>
It's possible to have a key type in a module. In fact, some of the existing key
types such as key_type_rxrpc can already be modular. But I don't think it
really works as intended currently because there is no autoloading of key type
modules. That is, if big_key was a module and you tried to add a key of type
"big_key", the big_key module would *not* be automatically loaded, so the call
would return -ENODEV. This could be fixed, I believe.
(I also still need to convince myself that there aren't any race conditions in
key type unregistering. It's a little weird how it changes the key type to the
".dead" key type, rather than pinning the key type in memory while it's still
used.)
Eric
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