Re: [PATCH] crypto: af_alg - Document the deprecation of AF_ALG

[Eric Biggers <ebiggers@kernel.org>]

On Tue, May 05, 2026 at 04:17:18PM -0700, Andy Lutomirski wrote:
> > On Apr 29, 2026, at 6:19 PM, Eric Biggers <ebiggers@kernel.org> wrote:
> >
> > AF_ALG is almost completely unnecessary, and it exposes a massive attack
> > surface that hasn't been standing up to modern vulnerability discovery
> > tools.  The latest one even has its own website, providing a small
> > Python script that reliably roots most Linux distros: https://copy.fail/
> 
> How about adding a configuration option, defaulted on, that requires
> capable(CAP_SYS_ADMIN) to create the socket (and maybe also to bind /
> connect it).  And a sysctl to allow the administrator to override this
> in the unlikely event that it’s needed.
> 
> IIRC cryptsetup used to and maybe even still does require these
> sockets sometimes and this would let it keep working.  And there's all
> the FIPS stuff downthread.

Yes, I'd like to add a default-on requirement to hold a capability in
the initial user namespace.  We're trying to figure out the details.

It sounds like iwd runs with CAP_NET_ADMIN, not necessarily
CAP_SYS_ADMIN.  So it may need to be:

    has_capability_noaudit(current, CAP_NET_ADMIN) || capable(CAP_SYS_ADMIN)

iwd is being discussed in the thread
https://lore.kernel.org/linux-crypto/bcbbef00-5881-421b-8892-7be6c04b832d@gmail.com/

cryptsetup is normally run with CAP_SYS_ADMIN, but not always (e.g.,
'cryptsetup benchmark').  It might be acceptable for users to add sudo
in the exceptional cases.  cryptsetup is being discussed in the thread
https://lore.kernel.org/linux-crypto/5dd3be22-13fb-41fb-b469-1ae6472200b1@gmail.com/

bluez needs investigation.

- Eric