Re: [PATCH v1 6/7] NFSD: Add filehandle crypto functions and helpers

[Eric Biggers <ebiggers@kernel.org>]

On Sat, Dec 27, 2025 at 08:34:18PM -0500, Chuck Lever wrote:
> I'd feel more comfortable if the crypto community had a look
> to ensure that we're utilizing the APIs in the most efficient
> way possible. Adding linux-crypto ...

Many crypto algorithms (especially hash algorithms and MACs) have
library APIs now.  They're much easier to use than the traditional APIs.

But it's too soon to be discussing which API to use.  Looking at the
whole series in lore, there doesn't seem to be any explanation of what
problem this series is trying to solve and how cryptography is being
used to solve that problem.

The choice of AES-CBC encryption is unusual.  It's unlikely to be an
appropriate choice for the problem.

I suspect you're really looking to protect the authenticity of the file
handles, not their confidentiality; i.e., you'd like to prevent clients
from constructing their own file handles.  In that case you'd probably
need a MAC, such as SipHash or HMAC-SHA256.  This would be similar to
the kernel's existing implementations of TCP SYN and SCTP cookies: the
system sends out cookies that encode some information, and it uses a MAC
to verify that any received cookie is a previously sent one.

But that's just what I suspect.  I can't know for sure since this series
doesn't provide any context about what it's trying to achieve.

- Eric