ima: allocate field pointers array on demand in template_desc_init_fields()

The allocation of a field pointers array is moved at the end of
template_desc_init_fields() and done only if the value of the 'fields'
and 'num_fields' parameters is not NULL. For just validating a template
format string, retrieved template field pointers are placed in a temporary
array.

Changelog:
 - v3:
   - do not check in this patch if 'fields' and 'num_fields' are NULL
     (suggested by Mimi Zohar)

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

1 files changed, 13 insertions, 21 deletions

diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index d93a58e603df..65117ba06809 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -117,8 +117,9 @@ static int template_desc_init_fields(const char *template_fmt,
                                      int *num_fields)
 {
         const char *template_fmt_ptr;
+        struct ima_template_field *found_fields[IMA_TEMPLATE_NUM_FIELDS_MAX];
         int template_num_fields = template_fmt_size(template_fmt);
-        int i, len, result = 0;
+        int i, len;
 
         if (template_num_fields > IMA_TEMPLATE_NUM_FIELDS_MAX) {
                 pr_err("format string '%s' contains too many fields\n",
@@ -126,41 +127,32 @@ static int template_desc_init_fields(const char *template_fmt,
                 return -EINVAL;
         }
 
-        *fields = kzalloc(template_num_fields * sizeof(*fields), GFP_KERNEL);
-        if (*fields == NULL) {
-                result = -ENOMEM;
-                goto out;
-        }
-
         for (i = 0, template_fmt_ptr = template_fmt; i < template_num_fields;
              i++, template_fmt_ptr += len + 1) {
                 char tmp_field_id[IMA_TEMPLATE_FIELD_ID_MAX_LEN + 1];
-                struct ima_template_field *f;
 
                 len = strchrnul(template_fmt_ptr, '|') - template_fmt_ptr;
                 if (len == 0 || len > IMA_TEMPLATE_FIELD_ID_MAX_LEN) {
                         pr_err("Invalid field with length %d\n", len);
-                        result = -EINVAL;
-                        goto out;
+                        return -EINVAL;
                 }
 
                 memcpy(tmp_field_id, template_fmt_ptr, len);
                 tmp_field_id[len] = '\0';
-                f = lookup_template_field(tmp_field_id);
-                if (!f) {
+                found_fields[i] = lookup_template_field(tmp_field_id);
+                if (!found_fields[i]) {
                         pr_err("field '%s' not found\n", tmp_field_id);
-                        result = -ENOENT;
-                        goto out;
+                        return -ENOENT;
                 }
-                (*fields)[i] = f;
         }
+
+        *fields = kmalloc_array(i, sizeof(*fields), GFP_KERNEL);
+        if (*fields == NULL)
+                return -ENOMEM;
+
+        memcpy(*fields, found_fields, i * sizeof(*fields));
         *num_fields = i;
-out:
-        if (result < 0) {
-                kfree(*fields);
-                *fields = NULL;
-        }
-        return result;
+        return 0;
 }
 
 struct ima_template_desc *ima_template_desc_current(void)