diff --git a/security/caitsith/realpath.c b/security/caitsith/realpath.c
new file mode 100644
index 0000000..f62d843
--- /dev/null
+++ b/security/caitsith/realpath.c
@@ -0,0 +1,227 @@
+/*
+ * security/caitsith/realpath.c
+ *
+ * Copyright (C) 2005-2012  NTT DATA CORPORATION
+ */
+
+#include "caitsith.h"
+
+/**
+ * cs_realpath - Returns realpath(3) of the given pathname but ignores chroot'ed root.
+ *
+ * @path: Pointer to "struct path".
+ *
+ * Returns the realpath of the given @path on success, NULL otherwise.
+ *
+ * This function uses kzalloc(), so caller must kfree() if this function
+ * didn't return NULL.
+ */
+char *cs_realpath(const struct path *path)
+{
+	char *buf = NULL;
+	char *name = NULL;
+	unsigned int buf_len = PAGE_SIZE / 2;
+	struct dentry *dentry = path->dentry;
+	struct super_block *sb;
+
+	if (!dentry)
+		return NULL;
+	sb = dentry->d_sb;
+	while (1) {
+		char *pos;
+
+		buf_len <<= 1;
+		kfree(buf);
+		buf = kmalloc(buf_len, GFP_NOFS);
+		if (!buf)
+			break;
+		/* To make sure that pos is '\0' terminated. */
+		buf[buf_len - 1] = '\0';
+		/* For "pipe:[\$]". */
+		if (dentry->d_op && dentry->d_op->d_dname)
+			pos = dentry->d_op->d_dname(dentry, buf, buf_len - 1);
+		else
+			pos = d_absolute_path(path, buf, buf_len);
+		if (IS_ERR(pos))
+			continue;
+		name = cs_encode(pos);
+		break;
+	}
+	kfree(buf);
+	if (!name)
+		cs_warn_oom(__func__);
+	return name;
+}
+
+/**
+ * cs_encode2 - Encode binary string to ascii string.
+ *
+ * @str:     String in binary format. Maybe NULL.
+ * @str_len: Size of @str in byte.
+ *
+ * Returns pointer to @str in ascii format on success, NULL otherwise.
+ *
+ * This function uses kzalloc(), so caller must kfree() if this function
+ * didn't return NULL.
+ */
+static char *cs_encode2(const char *str, int str_len)
+{
+	int i;
+	int len;
+	const char *p = str;
+	char *cp;
+	char *cp0;
+
+	if (!p)
+		return NULL;
+	len = str_len;
+	for (i = 0; i < str_len; i++) {
+		const unsigned char c = p[i];
+
+		if (!(c > ' ' && c < 127 && c != '\\'))
+			len += 3;
+	}
+	len++;
+	cp = kzalloc(len, GFP_NOFS);
+	if (!cp)
+		return NULL;
+	cp0 = cp;
+	p = str;
+	for (i = 0; i < str_len; i++) {
+		const unsigned char c = p[i];
+
+		if (c > ' ' && c < 127 && c != '\\') {
+			*cp++ = c;
+		} else {
+			*cp++ = '\\';
+			*cp++ = (c >> 6) + '0';
+			*cp++ = ((c >> 3) & 7) + '0';
+			*cp++ = (c & 7) + '0';
+		}
+	}
+	return cp0;
+}
+
+/**
+ * cs_encode - Encode binary string to ascii string.
+ *
+ * @str: String in binary format. Maybe NULL.
+ *
+ * Returns pointer to @str in ascii format on success, NULL otherwise.
+ *
+ * This function uses kzalloc(), so caller must kfree() if this function
+ * didn't return NULL.
+ */
+char *cs_encode(const char *str)
+{
+	return str ? cs_encode2(str, strlen(str)) : NULL;
+}
+
+/**
+ * cs_const_part_length - Evaluate the initial length without a pattern in a token.
+ *
+ * @filename: The string to evaluate. Maybe NULL.
+ *
+ * Returns the initial length without a pattern in @filename.
+ */
+static int cs_const_part_length(const char *filename)
+{
+	char c;
+	int len = 0;
+
+	if (!filename)
+		return 0;
+	while (1) {
+		c = *filename++;
+		if (!c)
+			break;
+		if (c != '\\') {
+			len++;
+			continue;
+		}
+		c = *filename++;
+		switch (c) {
+		case '0':   /* "\ooo" */
+		case '1':
+		case '2':
+		case '3':
+			c = *filename++;
+			if (c < '0' || c > '7')
+				break;
+			c = *filename++;
+			if (c < '0' || c > '7')
+				break;
+			len += 4;
+			continue;
+		}
+		break;
+	}
+	return len;
+}
+
+/**
+ * cs_fill_path_info - Fill in "struct cs_path_info" members.
+ *
+ * @ptr: Pointer to "struct cs_path_info" to fill in.
+ *
+ * Returns nothing.
+ *
+ * The caller sets "struct cs_path_info"->name.
+ */
+void cs_fill_path_info(struct cs_path_info *ptr)
+{
+	const char *name = ptr->name;
+	const int len = strlen(name);
+
+	ptr->total_len = len;
+	ptr->const_len = cs_const_part_length(name);
+	ptr->hash = full_name_hash(NULL, name, len);
+}
+
+/**
+ * cs_get_exe - Get cs_realpath() of current process.
+ *
+ * Returns the cs_realpath() of current process on success, NULL otherwise.
+ *
+ * This function uses kzalloc(), so the caller must kfree()
+ * if this function didn't return NULL.
+ */
+char *cs_get_exe(void)
+{
+	struct mm_struct *mm = current->mm;
+	char *cp;
+	struct file *exe_file;
+
+	if (current->flags & PF_KTHREAD)
+		return kstrdup("<kernel>", GFP_NOFS);
+	if (!mm)
+		goto task_has_no_mm;
+	exe_file = get_mm_exe_file(mm);
+	if (!exe_file)
+		goto task_has_no_mm;
+	cp = cs_realpath(&exe_file->f_path);
+	fput(exe_file);
+	return cp;
+task_has_no_mm:
+	return kstrdup("<unknown>", GFP_NOFS);
+}
+
+/**
+ * cs_get_exename - Get cs_realpath() of current process.
+ *
+ * @buf: Pointer to "struct cs_path_info".
+ *
+ * Returns true on success, false otherwise.
+ *
+ * This function uses kzalloc(), so the caller must kfree()
+ * if this function returned true.
+ */
+bool cs_get_exename(struct cs_path_info *buf)
+{
+	buf->name = cs_get_exe();
+	if (buf->name) {
+		cs_fill_path_info(buf);
+		return true;
+	}
+	return false;
+}
