ima: check return value of crypto_shash_final() in boot aggregate

The return value of crypto_shash_final() is not checked in
ima_calc_boot_aggregate_tfm(). If the hash finalization fails, the
function returns success and a corrupted boot aggregate digest could
be used for IMA measurements.

Capture the return value and propagate any error to the caller.

Fixes: 76bb28f ("ima: use new crypto_shash API instead of old crypto_hash")
Signed-off-by: Daniel Hodges <hodgesd@meta.com>
Reviewed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Author: hodgesds

security/integrity/ima/ima_crypto.c

@@ -838,7 +838,7 @@ static int ima_calc_boot_aggregate_tfm(char *digest, u16 alg_id,
 		}
 	}
 	if (!rc)
-		crypto_shash_final(shash, digest);
+		rc = crypto_shash_final(shash, digest);
 	return rc;
 }