LSM: SafeSetID: refactor policy parsing

In preparation for changing the policy parsing logic, refactor the line
parsing logic to be less verbose and move it into a separate function.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>

diff --git a/security/safesetid/securityfs.c b/security/safesetid/securityfs.c
index 2c6c829..90784a8 100644 (file)
--- a/security/safesetid/securityfs.c
+++ b/security/safesetid/securityfs.c
@@ -33,68 +33,50 @@ static struct safesetid_file_entry safesetid_files[] = {
 
 /*
  * In the case the input buffer contains one or more invalid UIDs, the kuid_t
- * variables pointed to by 'parent' and 'child' will get updated but this
+ * variables pointed to by @parent and @child will get updated but this
  * function will return an error.
+ * Contents of @buf may be modified.
  */
-static int parse_safesetid_whitelist_policy(const char __user *buf,
-                                           size_t len,
-                                           kuid_t *parent,
-                                           kuid_t *child)
+static int parse_policy_line(
+       struct file *file, char *buf, kuid_t *parent, kuid_t *child)
 {
-       char *kern_buf;
-       char *parent_buf;
-       char *child_buf;
-       const char separator[] = ":";
+       char *child_str;
        int ret;
-       size_t first_substring_length;
-       long parsed_parent;
-       long parsed_child;
+       u32 parsed_parent, parsed_child;
 
-       /* Duplicate string from user memory and NULL-terminate */
-       kern_buf = memdup_user_nul(buf, len);
-       if (IS_ERR(kern_buf))
-               return PTR_ERR(kern_buf);
-
-       /*
-        * Format of |buf| string should be <UID>:<UID>.
-        * Find location of ":" in kern_buf (copied from |buf|).
-        */
-       first_substring_length = strcspn(kern_buf, separator);
-       if (first_substring_length == 0 || first_substring_length == len) {
-               ret = -EINVAL;
-               goto free_kern;
-       }
-
-       parent_buf = kmemdup_nul(kern_buf, first_substring_length, GFP_KERNEL);
-       if (!parent_buf) {
-               ret = -ENOMEM;
-               goto free_kern;
-       }
+       /* Format of |buf| string should be <UID>:<UID>. */
+       child_str = strchr(buf, ':');
+       if (child_str == NULL)
+               return -EINVAL;
+       *child_str = '\0';
+       child_str++;
 
-       ret = kstrtol(parent_buf, 0, &parsed_parent);
+       ret = kstrtou32(buf, 0, &parsed_parent);
        if (ret)
-               goto free_both;
+               return ret;
 
-       child_buf = kern_buf + first_substring_length + 1;
-       ret = kstrtol(child_buf, 0, &parsed_child);
+       ret = kstrtou32(child_str, 0, &parsed_child);
        if (ret)
-               goto free_both;
+               return ret;
 
        *parent = make_kuid(current_user_ns(), parsed_parent);
-       if (!uid_valid(*parent)) {
-               ret = -EINVAL;
-               goto free_both;
-       }
-
        *child = make_kuid(current_user_ns(), parsed_child);
-       if (!uid_valid(*child)) {
-               ret = -EINVAL;
-               goto free_both;
-       }
+       if (!uid_valid(*parent) || !uid_valid(*child))
+               return -EINVAL;
 
-free_both:
-       kfree(parent_buf);
-free_kern:
+       return 0;
+}
+
+static int parse_safesetid_whitelist_policy(
+       struct file *file, const char __user *buf, size_t len,
+       kuid_t *parent, kuid_t *child)
+{
+       char *kern_buf = memdup_user_nul(buf, len);
+       int ret;
+
+       if (IS_ERR(kern_buf))
+               return PTR_ERR(kern_buf);
+       ret = parse_policy_line(file, kern_buf, parent, child);
        kfree(kern_buf);
        return ret;
 }
@@ -121,8 +103,8 @@ static ssize_t safesetid_file_write(struct file *file,
                flush_safesetid_whitelist_entries();
                break;
        case SAFESETID_WHITELIST_ADD:
-               ret = parse_safesetid_whitelist_policy(buf, len, &parent,
-                                                                &child);
+               ret = parse_safesetid_whitelist_policy(file, buf, len,
+                                                      &parent, &child);
                if (ret)
                        return ret;