Re: please consider disabling obsolete crypto in 5.10 and later
On Wed, 10 Mar 2021 at 14:38, Salvatore Bonaccorso <carnil@debian.org> wrote:
>
> Hi Ard,
>
> On Tue, Mar 09, 2021 at 05:45:01PM +0100, Ard Biesheuvel wrote:
> > On Thu, 25 Feb 2021 at 12:06, Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > On Thu, 25 Feb 2021 at 11:35, Salvatore Bonaccorso <carnil@debian.org> wrote:
> > > >
> > > > Hi Ard,
> > > >
> > > > On Mon, Feb 01, 2021 at 10:21:27PM +0100, Salvatore Bonaccorso wrote:
> > > > > Hi Ard,
> > > > >
> > > > > On Sat, Jan 30, 2021 at 04:41:16PM +0100, Ard Biesheuvel wrote:
> > > > > > L.S.,
> > > > > >
> > > > > > This is a request to consider disabling obsolete crypto in 5.10 and
> > > > > > later Debian builds of the Linux kernel on any architecture.
> > > > > >
> > > > > > We are all familiar with the rigid rules when it comes to not breaking
> > > > > > userspace by making changes to the kernel, but this rule only takes
> > > > > > effect when anybody notices, and so I am proposing disabling some code
> > > > > > downstream before removing it entirely.
> > > > > >
> > > > > > 5.10 introduces a new Kconfig symbol
> > > > > >
> > > > > > CONFIG_CRYPTO_USER_API_ENABLE_OBSOLETE
> > > > > >
> > > > > > which is enabled by default, but depends on support for the AF_ALG
> > > > > > socket API being enabled. In turn, block ciphers that are obsolete and
> > > > > > unlikely to be used anywhere have been made to depend on this new
> > > > > > symbol.
> > > > > >
> > > > > > This means that these obsolete block ciphers will disappear entirely
> > > > > > when the AF_ALG socket API is omitted, but we can get rid of these
> > > > > > block ciphers explicitly too, by not setting the new symbol. I.e.,
> > > > > > adding
> > > > > >
> > > > > > # CONFIG_CRYPTO_USER_API_ENABLE_OBSOLETE is not set
> > > > > >
> > > > > > to the kernel configs. Note that Fedora have already done so in release 33 [0]
> > > > > >
> > > > > > The block ciphers in question are RC4, Khazad, SEED, and
> > > > > > TEA/XTEA/XETA, none of which are used by the kernel itself, or known
> > > > > > to be used via the socket API (although a change was applied to
> > > > > > iwd/libell recently to get rid of an occurrence of RC4 - this change
> > > > > > has already been pulled into bullseye afaik)
> > > > > >
> > > > > > Note that this is not a statement on whether these algorithms are
> > > > > > secure or not -there is simply no point in carrying and shipping code
> > > > > > that nobody uses or audits, but which can be autoloaded and exercised
> > > > > > via an unprivileged interface.
> > > > >
> > > > > FTR (posteriori), we tried that in
> > > > > https://salsa.debian.org/kernel-team/linux/-/commit/633e1992f7d915c22b2a2adea87981e7503bb737
> > > > > (and is in the 5.10.12-1 upload to unstable).
> > > >
> > > > There were two reports which might be in the end related to that
> > > > change:
> > > >
> > > > https://bugs.debian.org/979764
> > > > https://bugs.debian.org/983508
> > > >
> > > > We have long that nfs-utils need to be updated, but the version was so
> > > > outdated, that progress on updating to a newer version stalled, and
> > > > could not be done in time for bulleye. Once bullseye is released I
> > > > guess this really needs to be prioritzed in some way.
> > > >
> > > > Ard, have you any insight in the above, so, should we revert the above
> > > > change for bullseye again?
> > > >
> > >
> > > Hello Salvatore,
> > >
> > > I think the issue is the patch below. Having something that requires
> > > RC4 and MD5 for security is an absolute joke in 2021, so I won't
> > > recommend you reverting it. Instead, you should really fix nfs-utils
> > > with priority.
> > >
> >
> > Any updates on this?
>
> Apologies for not replying earlier. I agree with you.
>
> Debian's nfs-utils situation is quite bad. As you might know we still
> ship 1.3.4, which at best is ancient with respect to upstream. Worse,
> we cannot update it at this stage of the freeze (cf.
> https://release.debian.org/#release-dates).
>
> So I guess the only two options we have now is either to revert the
> above commit you think is the cause of the issues reported, or if this
> is feasible apply the needed changes for nfs-utils (if they can be
> determined and can be applied to the old version).
>
Reverting the patch in question in the distro kernel seems reasonable,
but please keep it as a downstream change only. Note that you will
also need to revert the CONFIG_CRYPTO_USER_API_ENABLE_OBSOLETE change,
or re-enable the ecb(arc4) driver in another way, because the NFS code
relies on RC4.
> After the Debian bullseye release it defintively needs to be a
> priority for nfs-utils to be rebased to 2.5.3 and later (and then in
> particular keep up with rebasing it, and not fall into the same issue
> again).
>
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