On Fri, 2018-03-16 at 17:38 -0300, Thiago Jung Bauermann wrote:
> IMA will need to access the digest of the PKCS7 message (as calculated by
> the kernel) before the signature is verified, so introduce
> pkcs7_get_digest() for that purpose.
>
> Also, modify pkcs7_digest() to detect when the digest was already
> calculated so that it doesn't have to do redundant work. Verifying that
> sinfo->sig->digest isn't NULL is sufficient because both places which
> allocate sinfo->sig (pkcs7_parse_message() and pkcs7_note_signed_info())
> use kzalloc() so sig->digest is always initialized to zero.
>
> Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxxxxxxx>
> Cc: David Howells <dhowells@xxxxxxxxxx>
> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> ---
> crypto/asymmetric_keys/pkcs7_verify.c | 25 +++++++++++++++++++++++++
> include/crypto/pkcs7.h | 3 +++
> 2 files changed, 28 insertions(+)
>
> diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
> index 39e6de0c2761..bd02360f8be5 100644
> --- a/crypto/asymmetric_keys/pkcs7_verify.c
> +++ b/crypto/asymmetric_keys/pkcs7_verify.c
> @@ -33,6 +33,10 @@ static int pkcs7_digest(struct pkcs7_message *pkcs7,
>
> kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
>
> + /* The digest was calculated already. */
> + if (sig->digest)
> + return 0;
> +
> if (!sinfo->sig->hash_algo)
> return -ENOPKG;
>
> @@ -122,6 +126,27 @@ static int pkcs7_digest(struct pkcs7_message *pkcs7,
> return ret;
> }
>
> +int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u8 *len)
> +{
> + struct pkcs7_signed_info *sinfo = pkcs7->signed_infos;
> + int ret;
> +
> + /*
> + * This function doesn't support messages with more than one signature.
> + */
> + if (sinfo == NULL || sinfo->next != NULL)
> + return -EBADMSG;
> +
> + ret = pkcs7_digest(pkcs7, sinfo);
> + if (ret)
> + return ret;
> +
> + *buf = sinfo->sig->digest;
> + *len = sinfo->sig->digest_size;
> +
> + return 0;
> +}
> +
> /*
> * Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7
> * uses the issuer's name and the issuing certificate serial number for
> diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
> index 6f51d0cb6d12..cfaea9c37f4a 100644
> --- a/include/crypto/pkcs7.h
> +++ b/include/crypto/pkcs7.h
> @@ -46,4 +46,7 @@ extern int pkcs7_verify(struct pkcs7_message *pkcs7,
> extern int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
> const void *data, size_t datalen);
>
> +extern int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf,
> + u8 *len);
> +
> #endif /* _CRYPTO_PKCS7_H */
>
