evm: digital signature verification support

This patch adds support for digital signature verification to EVM.
With this feature file metadata can be protected using digital
signature instead of an HMAC. When building an image,
which has to be flashed to different devices, an HMAC cannot
be used to sign file metadata, because the HMAC key should be
different on every device.

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Acked-by: Mimi Zohar <zohar@us.ibm.com>

1 files changed, 81 insertions, 13 deletions

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 92d3d99a9f7b..8901501425f4 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -25,6 +25,7 @@
 int evm_initialized;
 
 char *evm_hmac = "hmac(sha1)";
+char *evm_hash = "sha1";
 
 char *evm_config_xattrnames[] = {
 #ifdef CONFIG_SECURITY_SELINUX
@@ -46,6 +47,29 @@ static int __init evm_set_fixmode(char *str)
 }
 __setup("evm=", evm_set_fixmode);
 
+static int evm_find_protected_xattrs(struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	char **xattr;
+	int error;
+	int count = 0;
+
+	if (!inode->i_op || !inode->i_op->getxattr)
+		return -EOPNOTSUPP;
+
+	for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
+		error = inode->i_op->getxattr(dentry, *xattr, NULL, 0);
+		if (error < 0) {
+			if (error == -ENODATA)
+				continue;
+			return error;
+		}
+		count++;
+	}
+
+	return count;
+}
+
 /*
  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
  *
@@ -65,32 +89,72 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 					     size_t xattr_value_len,
 					     struct integrity_iint_cache *iint)
 {
-	struct evm_ima_xattr_data xattr_data;
+	struct evm_ima_xattr_data *xattr_data = NULL;
+	struct evm_ima_xattr_data calc;
 	enum integrity_status evm_status = INTEGRITY_PASS;
-	int rc;
+	int rc, xattr_len;
 
 	if (iint && iint->evm_status == INTEGRITY_PASS)
 		return iint->evm_status;
 
 	/* if status is not PASS, try to check again - against -ENOMEM */
 
-	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
-			   xattr_value_len, xattr_data.digest);
-	if (rc < 0) {
-		evm_status = (rc == -ENODATA)
-		    ? INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
+	/* first need to know the sig type */
+	rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
+				GFP_NOFS);
+	if (rc <= 0) {
+		if (rc == 0)
+			evm_status = INTEGRITY_FAIL; /* empty */
+		else if (rc == -ENODATA) {
+			rc = evm_find_protected_xattrs(dentry);
+			if (rc > 0)
+				evm_status = INTEGRITY_NOLABEL;
+			else if (rc == 0)
+				evm_status = INTEGRITY_NOXATTRS; /* new file */
+		}
 		goto out;
 	}
 
-	xattr_data.type = EVM_XATTR_HMAC;
-	rc = vfs_xattr_cmp(dentry, XATTR_NAME_EVM, (u8 *)&xattr_data,
-			   sizeof xattr_data, GFP_NOFS);
-	if (rc < 0)
-		evm_status = (rc == -ENODATA)
-		    ? INTEGRITY_NOLABEL : INTEGRITY_FAIL;
+	xattr_len = rc - 1;
+
+	/* check value type */
+	switch (xattr_data->type) {
+	case EVM_XATTR_HMAC:
+		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
+				   xattr_value_len, calc.digest);
+		if (rc)
+			break;
+		rc = memcmp(xattr_data->digest, calc.digest,
+			    sizeof(calc.digest));
+		if (rc)
+			rc = -EINVAL;
+		break;
+	case EVM_IMA_XATTR_DIGSIG:
+		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
+				xattr_value_len, calc.digest);
+		if (rc)
+			break;
+		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
+					xattr_data->digest, xattr_len,
+					calc.digest, sizeof(calc.digest));
+		if (!rc) {
+			/* we probably want to replace rsa with hmac here */
+			evm_update_evmxattr(dentry, xattr_name, xattr_value,
+				   xattr_value_len);
+		}
+		break;
+	default:
+		rc = -EINVAL;
+		break;
+	}
+
+	if (rc)
+		evm_status = (rc == -ENODATA) ?
+				INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
 out:
 	if (iint)
 		iint->evm_status = evm_status;
+	kfree(xattr_data);
 	return evm_status;
 }
 
@@ -354,6 +418,8 @@ static int __init init_evm(void)
 		printk(KERN_INFO "EVM: Error registering secfs\n");
 		goto err;
 	}
+
+	return 0;
 err:
 	return error;
 }
@@ -363,6 +429,8 @@ static void __exit cleanup_evm(void)
 	evm_cleanup_secfs();
 	if (hmac_tfm)
 		crypto_free_shash(hmac_tfm);
+	if (hash_tfm)
+		crypto_free_shash(hash_tfm);
 }
 
 /*