[dm-devel] [PATCH] crypto: mark unused ciphers as obsolete

[Van Leeuwen, Pascal]

> -----Original Message-----
> From: Ard Biesheuvel <ardb at kernel.org>
> Sent: Friday, September 11, 2020 6:30 PM
> To: Van Leeuwen, Pascal <pvanleeuwen at rambus.com>; dm-devel at redhat.com; Milan Broz <gmazyland at gmail.com>
> Cc: linux-crypto at vger.kernel.org; herbert at gondor.apana.org.au; ebiggers at kernel.org
> Subject: Re: [PATCH] crypto: mark unused ciphers as obsolete
>
> <<< External Email >>>
> (cc Milan and dm-devel)
>
> On Fri, 11 Sep 2020 at 19:24, Van Leeuwen, Pascal
> <pvanleeuwen at rambus.com> wrote:
> >
> > > -----Original Message-----
> > > From: linux-crypto-owner at vger.kernel.org <linux-crypto-owner at vger.kernel.org> On Behalf Of Ard Biesheuvel
> > > Sent: Friday, September 11, 2020 4:11 PM
> > > To: linux-crypto at vger.kernel.org
> > > Cc: herbert at gondor.apana.org.au; ebiggers at kernel.org; Ard Biesheuvel <ardb at kernel.org>
> > > Subject: [PATCH] crypto: mark unused ciphers as obsolete
> > >
> > > <<< External Email >>>
> > > We have a few interesting pieces in our cipher museum, which are never
> > > used internally, and were only ever provided as generic C implementations.
> > >
> > > Unfortunately, we cannot simply remove this code, as we cannot be sure
> > > that it is not being used via the AF_ALG socket API, however unlikely.
> > > So let's mark the Anubis, Khazad, SEED and TEA algorithms as obsolete,
> > >
> > Wouldn't the IKE deamon be able to utilize these algorithms through the XFRM API?
> > I'm by no means an expert on the subject, but it looks like the cipher template is
> > provided there directly via XFRM, so it does not need to live in the kernel source.
> > And I know for a fact that SEED is being used for IPsec (and TLS) in Korea.
> >
>
> I have been staring at net/xfrm/xfrm_algo.c, and as far as I can tell,
> algorithms have to be mentioned there in order to be usable. None of
> the ciphers that this patch touches are listed there or anywhere else
> in the kernel.
>
Hmmm ... good point. Wasn't aware XFRM was actively allowing only a subset.
Actually found this commented out code in my Pluto source (kernel_netlink.c):

/*
 * Not yet implemented in Linux kernel xfrm_algo.c
{ SADB_X_EALG_SEEDCBC, "cbc(seed)" },
 */

Go figure.

> > The point being, there are more users to consider beyond "internal" (meaning hard
> > coded in the kernel source in this context?) and AF_ALG.
> >
>
> That is a good point, actually, since dm-crypt could be affected here
> as well, hence the CCs.
>
> Milan (or others): are you aware of any of these ciphers being used
> for dm-crypt?
>
>
> > I'm not aware of any real use cases for Anubis, Khazad and TEA though.
> >
>
> OK, thanks for confirming. Removing those would be a good start.
>
> > > which means they can only be enabled in the build if the socket API is
> > > enabled in the first place.
> > >
> > > Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> > > ---
> > > Hopefully, I will be able to convince the distro kernel maintainers to
> > > disable CRYPTO_USER_API_ENABLE_OBSOLETE in their v5.10+ builds once the
> > > iwd changes for arc4 make it downstream (Debian already has an updated
> > > version in its unstable distro). With the joint coverage of their QA,
> > > we should be able to confirm that these algos are never used, and
> > > actually remove them altogether.
> > >
> > >  crypto/Kconfig | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/crypto/Kconfig b/crypto/Kconfig
> > > index e85d8a059489..fac10143d23f 100644
> > > --- a/crypto/Kconfig
> > > +++ b/crypto/Kconfig
> > > @@ -1185,6 +1185,7 @@ config CRYPTO_AES_PPC_SPE
> > >
> > >  config CRYPTO_ANUBIS
> > >  tristate "Anubis cipher algorithm"
> > > +depends on CRYPTO_USER_API_ENABLE_OBSOLETE
> > >  select CRYPTO_ALGAPI
> > >  help
> > >    Anubis cipher algorithm.
> > > @@ -1424,6 +1425,7 @@ config CRYPTO_FCRYPT
> > >
> > >  config CRYPTO_KHAZAD
> > >  tristate "Khazad cipher algorithm"
> > > +depends on CRYPTO_USER_API_ENABLE_OBSOLETE
> > >  select CRYPTO_ALGAPI
> > >  help
> > >    Khazad cipher algorithm.
> > > @@ -1487,6 +1489,7 @@ config CRYPTO_CHACHA_MIPS
> > >
> > >  config CRYPTO_SEED
> > >  tristate "SEED cipher algorithm"
> > > +depends on CRYPTO_USER_API_ENABLE_OBSOLETE
> > >  select CRYPTO_ALGAPI
> > >  help
> > >    SEED cipher algorithm (RFC4269).
> > > @@ -1613,6 +1616,7 @@ config CRYPTO_SM4
> > >
> > >  config CRYPTO_TEA
> > >  tristate "TEA, XTEA and XETA cipher algorithms"
> > > +depends on CRYPTO_USER_API_ENABLE_OBSOLETE
> > >  select CRYPTO_ALGAPI
> > >  help
> > >    TEA cipher algorithm.
> > > --
> > > 2.17.1
> >
> > Regards,
> > Pascal van Leeuwen
> > Silicon IP Architect Multi-Protocol Engines, Rambus Security
> > Rambus ROTW Holding BV
> > +31-73 6581953
> >
> > Note: The Inside Secure/Verimatrix Silicon IP team was recently acquired by Rambus.
> > Please be so kind to update your e-mail address book with my new e-mail address.
> >
> >
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Regards,
Pascal van Leeuwen
Silicon IP Architect Multi-Protocol Engines, Rambus Security
Rambus ROTW Holding BV
+31-73 6581953

Note: The Inside Secure/Verimatrix Silicon IP team was recently acquired by Rambus.
Please be so kind to update your e-mail address book with my new e-mail address.


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