linux-kernel - Re: [PATCH v2] KEYS: asymmetric: Copy sig and digest in public_key_verify

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Date:   Mon, 12 Dec 2022 17:15:19 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     Eric Biggers <ebiggers@...nel.org>, dhowells@...hat.com,
        davem@...emloft.net, zohar@...ux.ibm.com,
        dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] KEYS: asymmetric: Copy sig and digest in
 public_key_verify_signature()

On Mon, Dec 12, 2022 at 10:07:38AM +0100, Roberto Sassu wrote:
>
> The problem is a misalignment between req->src_len (set to sig->s_size
> by akcipher_request_set_crypt()) and the length of the scatterlist (if
> we set the latter to sig->s_size + sig->digest_size).
> 
> When rsa_enc() calls mpi_read_raw_from_sgl(), it passes req->src_len as
> argument, and the latter allocates the MPI according to that. However,
> it does parsing depending on the length of the scatterlist.
> 
> If there are two scatterlists, it is not a problem, there is no
> misalignment. mpi_read_raw_from_sgl() picks the first. If there is just
> one, mpi_read_raw_from_sgl() parses all data there.

Thanks for the explanation.  That's definitely a bug which should
be fixed either in the RSA code or in MPI.

I'll look into it.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt