/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 * Copyright (C) 2006, 2007 University of Szeged, Hungary
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Authors: Artem Bityutskiy (Битюцкий Артём)
 *          Adrian Hunter
 *          Zoltan Sogor
 */

/*
 * This file implements UBIFS I/O subsystem which provides various I/O-related
 * helper functions (reading/writing/checking/validating nodes) and implements
 * write-buffering support. Write buffers help to save space which otherwise
 * would have been wasted for padding to the nearest minimal I/O unit boundary.
 * Instead, data first goes to the write-buffer and is flushed when the
 * buffer is full or when it is not used for some time (by timer). This is
 * similar to the mechanism is used by JFFS2.
 *
 * Write-buffers are defined by 'struct ubifs_wbuf' objects and protected by
 * mutexes defined inside these objects. Since sometimes upper-level code
 * has to lock the write-buffer (e.g. journal space reservation code), many
 * functions related to write-buffers have "nolock" suffix which means that the
 * caller has to lock the write-buffer before calling this function.
 *
 * UBIFS stores nodes at 64 bit-aligned addresses. If the node length is not
 * aligned, UBIFS starts the next node from the aligned address, and the padded
 * bytes may contain any rubbish. In other words, UBIFS does not put padding
 * bytes in those small gaps. Common headers of nodes store real node lengths,
 * not aligned lengths. Indexing nodes also store real lengths in branches.
 *
 * UBIFS uses padding when it pads to the next min. I/O unit. In this case it
 * uses padding nodes or padding bytes, if the padding node does not fit.
 *
 * All UBIFS nodes are protected by CRC checksums and UBIFS checks all nodes
 * every time they are read from the flash media.
 */

#include <linux/crc32.h>
#include "ubifs.h"

/**
 * ubifs_ro_mode - switch UBIFS to read read-only mode.
 * @c: UBIFS file-system description object
 * @err: error code which is the reason of switching to R/O mode
 */
void ubifs_ro_mode(struct ubifs_info *c, int err)
{
	if (!c->ro_media) {
		c->ro_media = 1;
		c->no_chk_data_crc = 0;
		ubifs_warn("switched to read-only mode, error %d", err);
		dbg_dump_stack();
	}
}

/**
 * ubifs_check_node - check node.
 * @c: UBIFS file-system description object
 * @buf: node to check
 * @lnum: logical eraseblock number
 * @offs: offset within the logical eraseblock
 * @quiet: print no messages
 * @must_chk_crc: indicates whether to always check the CRC
 *
 * This function checks node magic number and CRC checksum. This function also
 * validates node length to prevent UBIFS from becoming crazy when an attacker
 * feeds it a file-system image with incorrect nodes. For example, too large
 * node length in the common header could cause UBIFS to read memory outside of
 * allocated buffer when checking the CRC checksum.
 *
 * This function may skip data nodes CRC checking if @c->no_chk_data_crc is
 * true, which is controlled by corresponding UBIFS mount option. However, if
 * @must_chk_crc is true, then @c->no_chk_data_crc is ignored and CRC is
 * checked. Similarly, if @c->always_chk_crc is true, @c->no_chk_data_crc is
 * ignored and CRC is checked.
 *
 * This function returns zero in case of success and %-EUCLEAN in case of bad
 * CRC or magic.
 */
int ubifs_check_node(const struct ubifs_info *c, const void *buf, int lnum,
		     int offs, int quiet, int must_chk_crc)
{
	int err = -EINVAL, type, node_len;
	uint32_t crc, node_crc, magic;
	const struct ubifs_ch *ch = buf;

	ubifs_assert(lnum >= 0 && lnum < c->leb_cnt && offs >= 0);
	ubifs_assert(!(offs & 7) && offs < c->leb_size);

	magic = le32_to_cpu(ch->magic);
	if (magic != UBIFS_NODE_MAGIC) {
		if (!quiet)
			ubifs_err("bad magic %#08x, expected %#08x",
				  magic, UBIFS_NODE_MAGIC);
		err = -EUCLEAN;
		goto out;
	}

	type = ch->node_type;
	if (type < 0 || type >= UBIFS_NODE_TYPES_CNT) {
		if (!quiet)
			ubifs_err("bad node type %d", type);
		goto out;
	}

	node_len = le32_to_cpu(ch->len);
	if (node_len + offs > c->leb_size)
		goto out_len;

	if (c->ranges[type].max_len == 0) {
		if (node_len != c->ranges[type].len)
			goto out_len;
	} else if (node_len < c->ranges[type].min_len ||
		   node_len > c->ranges[type].max_len)
		goto out_len;

	if (!must_chk_crc && type == UBIFS_DATA_NODE && !c->always_chk_crc &&
	     c->no_chk_data_crc)
		return 0;

	crc = crc32(UBIFS_CRC32_INIT, buf + 8, node_len - 8);
	node_crc = le32_to_cpu(ch->crc);
	if (crc != node_crc) {
		if (!quiet)
			ubifs_err("bad CRC: calculated %#08x, read %#08x",
				  crc, node_crc);
		err = -EUCLEAN;
		goto out;
	}

	return 0;

out_len:
	if (!quiet)
		ubifs_err("bad node length %d", node_len);
out:
	if (!quiet) {
		ubifs_err("bad node at LEB %d:%d", lnum, offs);
		dbg_dump_node(c, buf);
		dbg_dump_stack();
	}
	return err;
}

/**
 * ubifs_pad - pad flash space.
 * @c: UBIFS file-system description object
 * @buf: buffer to put padding to
 * @pad: how many bytes to pad
 *
 * The flash media obliges us to write only in chunks of %c->min_io_size and