On Fri, 2018-03-16 at 17:38 -0300, Thiago Jung Bauermann wrote:
> IMA will only look for a modsig if the xattr sig references a key which is
> not in the expected kernel keyring. To that end, introduce
> asymmetric_sig_has_known_key().
>
> The logic of extracting the key used in the xattr sig is factored out from
> asymmetric_verify() so that it can be used by the new function.
>
> Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> ---
> security/integrity/digsig_asymmetric.c | 44 +++++++++++++++++++++++++---------
> security/integrity/integrity.h | 8 +++++++
> 2 files changed, 41 insertions(+), 11 deletions(-)
>
> diff --git a/security/integrity/digsig_asymmetric.c b/security/integrity/digsig_asymmetric.c
> index ab6a029062a1..241647970c19 100644
> --- a/security/integrity/digsig_asymmetric.c
> +++ b/security/integrity/digsig_asymmetric.c
> @@ -79,26 +79,48 @@ static struct key *request_asymmetric_key(struct key *keyring, uint32_t keyid)
> return key;
> }
>
> -int asymmetric_verify(struct key *keyring, const char *sig,
> - int siglen, const char *data, int datalen)
> +static struct key *asymmetric_key_from_sig(struct key *keyring, const char *sig,
> + int siglen)
> {
> - struct public_key_signature pks;
> - struct signature_v2_hdr *hdr = (struct signature_v2_hdr *)sig;
> - struct key *key;
> - int ret = -ENOMEM;
> + const struct signature_v2_hdr *hdr = (struct signature_v2_hdr *) sig;
>
> if (siglen <= sizeof(*hdr))
> - return -EBADMSG;
> + return ERR_PTR(-EBADMSG);
>
> siglen -= sizeof(*hdr);
>
> if (siglen != be16_to_cpu(hdr->sig_size))
> - return -EBADMSG;
> + return ERR_PTR(-EBADMSG);
>
> if (hdr->hash_algo >= HASH_ALGO__LAST)
> - return -ENOPKG;
> + return ERR_PTR(-ENOPKG);
> +
> + return request_asymmetric_key(keyring, be32_to_cpu(hdr->keyid));
> +}
> +
> +bool asymmetric_sig_has_known_key(struct key *keyring, const char *sig,
> + int siglen)
> +{
> + struct key *key;
> +
> + key = asymmetric_key_from_sig(keyring, sig, siglen);
> + if (IS_ERR_OR_NULL(key))
> + return false;
> +
> + key_put(key);
> +
> + return true;
> +}
> +
> +int asymmetric_verify(struct key *keyring, const char *sig,
> + int siglen, const char *data, int datalen)
> +{
> + struct public_key_signature pks;
> + struct signature_v2_hdr *hdr = (struct signature_v2_hdr *)sig;
> + struct key *key;
> + int ret = -ENOMEM;
>
> - key = request_asymmetric_key(keyring, be32_to_cpu(hdr->keyid));
> + key = asymmetric_key_from_sig(keyring, sig, siglen);
> if (IS_ERR(key))
> return PTR_ERR(key);
>
> @@ -109,7 +131,7 @@ int asymmetric_verify(struct key *keyring, const char *sig,
> pks.digest = (u8 *)data;
> pks.digest_size = datalen;
> pks.s = hdr->sig;
> - pks.s_size = siglen;
> + pks.s_size = siglen - sizeof(*hdr);
> ret = verify_signature(key, &pks);
> key_put(key);
> pr_debug("%s() = %d\n", __func__, ret);
> diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
> index 2d245f44ca26..4c381b992e11 100644
> --- a/security/integrity/integrity.h
> +++ b/security/integrity/integrity.h
> @@ -179,12 +179,20 @@ static inline int integrity_init_keyring(const unsigned int id)
> #ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS
> int asymmetric_verify(struct key *keyring, const char *sig,
> int siglen, const char *data, int datalen);
> +bool asymmetric_sig_has_known_key(struct key *keyring, const char *sig,
> + int siglen);
> #else
> static inline int asymmetric_verify(struct key *keyring, const char *sig,
> int siglen, const char *data, int datalen)
> {
> return -EOPNOTSUPP;
> }
> +
> +static inline bool asymmetric_sig_has_known_key(struct key *keyring,
> + const char *sig, int siglen)
> +{
> + return false;
> +}
> #endif
>
> #ifdef CONFIG_IMA_LOAD_X509
>
