ima: display template format in meas. list if template name length is zero

With the introduction of the 'ima_template_fmt' kernel cmdline parameter,
a user can define a new template descriptor with custom format. However,
in this case, userspace tools will be unable to parse the measurements
list because the new template is unknown. For this reason, this patch
modifies the current IMA behavior to display in the list the template
format instead of the name (only if the length of the latter is zero)
so that a tool can extract needed information if it can handle listed
fields.

This patch also correctly displays the error log message in
ima_init_template() if the selected template cannot be initialized.

Changelog:
 - v3:
   - check the first byte of 'e->template_desc->name' instead of using
     strlen() in ima_fs.c (suggested by Mimi Zohar)

 - v2:
   - print the template format in ima_init_template(), if the selected
     template is custom (Roberto Sassu)

 - v1:
   - fixed patch description (Roberto Sassu, suggested by Mimi Zohar)
   - set 'template_name' variable in ima_fs.c only once
     (Roberto Sassu, suggested by Mimi Zohar)
Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/ima/ima_fs.c

@@ -118,6 +118,7 @@ static int ima_measurements_show(struct seq_file *m, void *v)
 	/* the list never shrinks, so we don't need a lock here */
 	struct ima_queue_entry *qe = v;
 	struct ima_template_entry *e;
+	char *template_name;
 	int namelen;
 	u32 pcr = CONFIG_IMA_MEASURE_PCR_IDX;
 	bool is_ima_template = false;
@@ -128,6 +129,9 @@ static int ima_measurements_show(struct seq_file *m, void *v)
 	if (e == NULL)
 		return -1;
 
+	template_name = (e->template_desc->name[0] != '\0') ?
+	    e->template_desc->name : e->template_desc->fmt;
+
 	/*
 	 * 1st: PCRIndex
 	 * PCR used is always the same (config option) in
@@ -139,14 +143,14 @@ static int ima_measurements_show(struct seq_file *m, void *v)
 	ima_putc(m, e->digest, TPM_DIGEST_SIZE);
 
 	/* 3rd: template name size */
-	namelen = strlen(e->template_desc->name);
+	namelen = strlen(template_name);
 	ima_putc(m, &namelen, sizeof(namelen));
 
 	/* 4th:  template name */
-	ima_putc(m, e->template_desc->name, namelen);
+	ima_putc(m, template_name, namelen);
 
 	/* 5th:  template length (except for 'ima' template) */
-	if (strcmp(e->template_desc->name, IMA_TEMPLATE_IMA_NAME) == 0)
+	if (strcmp(template_name, IMA_TEMPLATE_IMA_NAME) == 0)
 		is_ima_template = true;
 
 	if (!is_ima_template)
@@ -200,6 +204,7 @@ static int ima_ascii_measurements_show(struct seq_file *m, void *v)
 	/* the list never shrinks, so we don't need a lock here */
 	struct ima_queue_entry *qe = v;
 	struct ima_template_entry *e;
+	char *template_name;
 	int i;
 
 	/* get entry */
@@ -207,6 +212,9 @@ static int ima_ascii_measurements_show(struct seq_file *m, void *v)
 	if (e == NULL)
 		return -1;
 
+	template_name = (e->template_desc->name[0] != '\0') ?
+	    e->template_desc->name : e->template_desc->fmt;
+
 	/* 1st: PCR used (config option) */
 	seq_printf(m, "%2d ", CONFIG_IMA_MEASURE_PCR_IDX);
 
@@ -214,7 +222,7 @@ static int ima_ascii_measurements_show(struct seq_file *m, void *v)
 	ima_print_digest(m, e->digest, TPM_DIGEST_SIZE);
 
 	/* 3th:  template name */
-	seq_printf(m, " %s", e->template_desc->name);
+	seq_printf(m, " %s", template_name);
 
 	/* 4th:  template specific data */
 	for (i = 0; i < e->template_desc->num_fields; i++) {

security/integrity/ima/ima_template.c

@@ -176,7 +176,9 @@ int __init ima_init_template(void)
 					   &(template->fields),
 					   &(template->num_fields));
 	if (result < 0)
-		pr_err("template %s init failed, result: %d\n", template->name);
+		pr_err("template %s init failed, result: %d\n",
+		       (strlen(template->name) ?
+		       template->name : template->fmt), result);
 
 	return result;
 }