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). Regards, Salvatore
