Re: [PATCH] libceph: Re-establish the FIPS keylength check in the Ceph code

[Eric Biggers]

On Fri, Aug 21, 2026 at 05:53:15PM +0000, Eric Biggers wrote:
> Do Ceph session keys shorter than 128 bits even actually occur in
> practice?  It seems that the Ceph authenticated modes support only
> AES-based cipher suites, where the minimum valid session key length is
> 128 bits.
> 
> I wonder if the client should just reject session_key_len < 16
> regardless of fips_enabled.

It looks like this is theoretically possible only when CEPH_AUTH_CEPHX
is being used but the session key uses CEPH_CRYPTO_NONE, which seems
insecure and contradictory, and likely not ever used by the server.  I
suspect the ceph client should just reject that combination outright
(and also session_key_len < 16 as defense-in-depth).  It is up to the
ceph folks who are the experts here, but if there are unnecessary
footguns like this, they should just be fixed for everyone.

- Eric