Re: [PATCH 1/1] crypto: authencesn: reject short ahash digests during instance creation

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Apr 20, 2026 at 11:21:54AM +0200, Ard Biesheuvel wrote:
> > diff --git a/crypto/authencesn.c b/crypto/authencesn.c
> > index 542a978663b9..bf44f035f7f8 100644
> > --- a/crypto/authencesn.c
> > +++ b/crypto/authencesn.c
> > @@ -384,6 +384,11 @@ static int crypto_authenc_esn_create(struct 
> > crypto_template *tmpl,
> >  		goto err_free_inst;
> >  	enc = crypto_spawn_skcipher_alg_common(&ctx->enc);
> > 
> > +	if (auth->digestsize > 0 && auth->digestsize < 4) {
> > +		err = -EINVAL;
> > +		goto err_free_inst;
> > +	}
> > +
> 
> Is this the best place for this check?

I probably would have put it a few lines earlier, right after the line
'auth_base = &auth->base;'.  But this works too.

Reviewed-by: Eric Biggers <ebiggers@kernel.org>

Of course, while this patch needs to be applied, this also doesn't go
nearly far enough.
https://lore.kernel.org/linux-crypto/20260420094120.5167-1-ardb@kernel.org/
removes the so-called "cipher_null", which has no reason to exist.

But "authencesn" itself should not be exposed to AF_ALG, let alone exist
in its current form at all.  The IPsec sequence numbers should just be
handled internally in the IPsec code itself.  That would be simpler and
more efficient, with much less UAPI surface as well.

- Eric