Re: please consider disabling obsolete crypto in 5.10 and later
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).
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).
Salvatore
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