audit: treat s_id as an untrusted string

The use of s_id should go through the untrusted string path, just to be
extra careful.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

security/integrity/ima/ima_audit.c

@@ -56,9 +56,11 @@ void integrity_audit_msg(int audit_msgno, struct inode *inode,
 		audit_log_format(ab, " name=");
 		audit_log_untrustedstring(ab, fname);
 	}
-	if (inode)
-		audit_log_format(ab, " dev=%s ino=%lu",
-				 inode->i_sb->s_id, inode->i_ino);
+	if (inode) {
+		audit_log_format(ab, " dev=");
+		audit_log_untrustedstring(ab, inode->i_sb->s_id);
+		audit_log_format(ab, " ino=%lu", inode->i_ino);
+	}
 	audit_log_format(ab, " res=%d", !result ? 0 : 1);
 	audit_log_end(ab);
 }