ima: Define asymmetric_verify_v3() to verify IMA sigv3 signatures

Define asymmetric_verify_v3() to calculate the hash of the struct
ima_file_id, before calling asymmetric_verify() to verify the
signature.

Move and update the existing calc_file_id_hash() function with a
simpler, self contained version.  In addition to the existing hash
data and hash data length arguments, also pass the hash algorithm.

Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Acked-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/digsig.c

@@ -59,7 +59,7 @@ static struct key *integrity_keyring_from_id(const unsigned int id)
 }
 
 int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
-			    const char *digest, int digestlen)
+			    const char *digest, int digestlen, u8 algo)
 {
 	struct key *keyring;
 
@@ -76,9 +76,11 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
 		return digsig_verify(keyring, sig + 1, siglen - 1, digest,
 				     digestlen);
 	case 2: /* regular file data hash based signature */
-	case 3: /* struct ima_file_id data based signature */
 		return asymmetric_verify(keyring, sig, siglen, digest,
-					 digestlen);
+					    digestlen);
+	case 3: /* struct ima_file_id data based signature */
+		return asymmetric_verify_v3(keyring, sig, siglen, digest,
+					    digestlen, algo);
 	}
 
 	return -EOPNOTSUPP;