ima: new templates management mechanism

The original 'ima' template is fixed length, containing the filedata hash
and pathname.  The filedata hash is limited to 20 bytes (md5/sha1).  The
pathname is a null terminated string, limited to 255 characters.  To
overcome these limitations and to add additional file metadata, it is
necessary to extend the current version of IMA by defining additional
templates.

The main reason to introduce this feature is that, each time a new
template is defined, the functions that generate and display the
measurement list would include the code for handling a new format and,
thus, would significantly grow over time.

This patch set solves this problem by separating the template management
from the remaining IMA code. The core of this solution is the definition
of two new data structures: a template descriptor, to determine which
information should be included in the measurement list, and a template
field, to generate and display data of a given type.

To define a new template field, developers define the field identifier
and implement two functions, init() and show(), respectively to generate
and display measurement entries.  Initially, this patch set defines the
following template fields (support for additional data types will be
added later):
 - 'd': the digest of the event (i.e. the digest of a measured file),
        calculated with the SHA1 or MD5 hash algorithm;
 - 'n': the name of the event (i.e. the file name), with size up to
        255 bytes;
 - 'd-ng': the digest of the event, calculated with an arbitrary hash
           algorithm (field format: [<hash algo>:]digest, where the digest
           prefix is shown only if the hash algorithm is not SHA1 or MD5);
 - 'n-ng': the name of the event, without size limitations.

Defining a new template descriptor requires specifying the template format,
a string of field identifiers separated by the '|' character.  This patch
set defines the following template descriptors:
 - "ima": its format is 'd|n';
 - "ima-ng" (default): its format is 'd-ng|n-ng'

Further details about the new template architecture can be found in
Documentation/security/IMA-templates.txt.

Changelog:
- don't defer calling ima_init_template() - Mimi
- don't define ima_lookup_template_desc() until used - Mimi
- squashed with documentation patch - Mimi

Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

1 files changed, 112 insertions, 0 deletions

diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
new file mode 100644
index 000000000000..7e86783ccf51
--- /dev/null
+++ b/security/integrity/ima/ima_template.c
@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2013 Politecnico di Torino, Italy
+ *                    TORSEC group -- http://security.polito.it
+ *
+ * Author: Roberto Sassu <roberto.sassu@polito.it>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2 of the
+ * License.
+ *
+ * File: ima_template.c
+ *      Helpers to manage template descriptors.
+ */
+#include "ima.h"
+
+static struct ima_template_desc defined_templates[] = {
+};
+
+static struct ima_template_field supported_fields[] = {
+};
+
+static struct ima_template_field *ima_lookup_template_field(
+							const char *field_id)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(supported_fields); i++)
+		if (strncmp(supported_fields[i].field_id, field_id,
+			    IMA_TEMPLATE_FIELD_ID_MAX_LEN) == 0)
+			return &supported_fields[i];
+	return NULL;
+}
+
+static int ima_template_fmt_size(char *template_fmt)
+{
+	char c;
+	int template_fmt_len = strlen(template_fmt);
+	int i = 0, j = 0;
+
+	while (i < template_fmt_len) {
+		c = template_fmt[i];
+		if (c == '|')
+			j++;
+		i++;
+	}
+
+	return j + 1;
+}
+
+static int template_desc_init_fields(char *template_fmt,
+				     struct ima_template_field ***fields,
+				     int *num_fields)
+{
+	char *c, *template_fmt_ptr = template_fmt;
+	int template_num_fields = ima_template_fmt_size(template_fmt);
+	int i, result = 0;
+
+	if (template_num_fields > IMA_TEMPLATE_NUM_FIELDS_MAX)
+		return -EINVAL;
+
+	*fields = kzalloc(template_num_fields * sizeof(*fields), GFP_KERNEL);
+	if (*fields == NULL) {
+		result = -ENOMEM;
+		goto out;
+	}
+	for (i = 0; (c = strsep(&template_fmt_ptr, "|")) != NULL &&
+	     i < template_num_fields; i++) {
+		struct ima_template_field *f = ima_lookup_template_field(c);
+
+		if (!f) {
+			result = -ENOENT;
+			goto out;
+		}
+		(*fields)[i] = f;
+	}
+	*num_fields = i;
+	return 0;
+out:
+	kfree(*fields);
+	*fields = NULL;
+	return result;
+}
+
+static int init_defined_templates(void)
+{
+	int i = 0;
+	int result = 0;
+
+	/* Init defined templates. */
+	for (i = 0; i < ARRAY_SIZE(defined_templates); i++) {
+		struct ima_template_desc *template = &defined_templates[i];
+
+		result = template_desc_init_fields(template->fmt,
+						   &(template->fields),
+						   &(template->num_fields));
+		if (result < 0)
+			return result;
+	}
+	return result;
+}
+
+int ima_init_template(void)
+{
+	int result;
+
+	result = init_defined_templates();
+	if (result < 0)
+		return result;
+
+	return 0;
+}