213 lines
5.3 KiB
C
213 lines
5.3 KiB
C
/*
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* Squashfs - a compressed read only filesystem for Linux
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*
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* Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
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* Phillip Lougher <phillip@squashfs.org.uk>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2,
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* or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* block.c
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*/
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/*
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* This file implements the low-level routines to read and decompress
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* datablocks and metadata blocks.
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*/
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#include <linux/fs.h>
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#include <linux/string.h>
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#include "squashfs_fs.h"
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#include "squashfs_fs_sb.h"
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#include "squashfs.h"
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#include "decompressor.h"
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#include "page_actor.h"
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/*
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* Read the metadata block length, this is stored in the first two
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* bytes of the metadata block.
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*/
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static char *get_block_length(struct super_block *sb,
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u64 *cur_index, int *offset, int *length)
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{
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struct squashfs_sb_info *msblk = sb->s_fs_info;
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char *buf;
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buf = squashfs_devread(msblk,
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*cur_index * msblk->devblksize,
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msblk->devblksize);
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if (buf == NULL)
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return NULL;
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if (msblk->devblksize - *offset == 1) {
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*length = (unsigned char) buf[*offset];
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free(buf);
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buf = squashfs_devread(msblk,
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++(*cur_index) * msblk->devblksize,
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msblk->devblksize);
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if (buf == NULL)
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return NULL;
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*length |= (unsigned char) buf[0] << 8;
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*offset = 1;
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} else {
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*length = (unsigned char) buf[*offset] |
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(unsigned char) buf[*offset + 1] << 8;
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*offset += 2;
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if (*offset == msblk->devblksize) {
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free(buf);
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buf = squashfs_devread(msblk,
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++(*cur_index) * msblk->devblksize,
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msblk->devblksize);
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if (buf == NULL)
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return NULL;
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*offset = 0;
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}
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}
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return buf;
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}
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/*
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* Read and decompress a metadata block or datablock. Length is non-zero
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* if a datablock is being read (the size is stored elsewhere in the
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* filesystem), otherwise the length is obtained from the first two bytes of
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* the metadata block. A bit in the length field indicates if the block
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* is stored uncompressed in the filesystem (usually because compression
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* generated a larger block - this does occasionally happen with compression
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* algorithms).
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*/
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int squashfs_read_data(struct super_block *sb, u64 index, int length,
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u64 *next_index, struct squashfs_page_actor *output)
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{
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struct squashfs_sb_info *msblk = sb->s_fs_info;
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char **buf;
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int offset = index & ((1 << msblk->devblksize_log2) - 1);
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u64 cur_index = index >> msblk->devblksize_log2;
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int bytes, compressed, b = 0, k = 0, avail;
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buf = calloc(((output->length + msblk->devblksize - 1)
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>> msblk->devblksize_log2) + 1, sizeof(*buf));
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if (buf == NULL)
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return -ENOMEM;
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if (length) {
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/*
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* Datablock.
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*/
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bytes = -offset;
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compressed = SQUASHFS_COMPRESSED_BLOCK(length);
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length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
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if (next_index)
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*next_index = index + length;
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TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
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index, compressed ? "" : "un", length, output->length);
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if (length < 0 || length > output->length ||
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(index + length) > msblk->bytes_used) {
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goto read_failure;
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}
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for (b = 0; bytes < length; b++, cur_index++) {
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buf[b] = squashfs_devread(msblk,
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cur_index * msblk->devblksize,
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msblk->devblksize);
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if (buf[b] == NULL)
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goto block_release;
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bytes += msblk->devblksize;
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}
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} else {
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/*
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* Metadata block.
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*/
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if ((index + 2) > msblk->bytes_used)
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goto read_failure;
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buf[0] = get_block_length(sb, &cur_index, &offset, &length);
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if (buf[0] == NULL)
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goto read_failure;
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b = 1;
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bytes = msblk->devblksize - offset;
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compressed = SQUASHFS_COMPRESSED(length);
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length = SQUASHFS_COMPRESSED_SIZE(length);
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if (next_index)
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*next_index = index + length + 2;
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TRACE("Block Meta @ 0x%llx, %scompressed size %d\n", index,
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compressed ? "" : "un", length);
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if (length < 0 || length > output->length ||
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(index + length) > msblk->bytes_used)
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goto block_release;
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for (; bytes < length; b++) {
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buf[b] = squashfs_devread(msblk,
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++cur_index * msblk->devblksize,
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msblk->devblksize);
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if (buf[b] == NULL)
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goto block_release;
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bytes += msblk->devblksize;
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}
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}
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if (compressed) {
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length = squashfs_decompress(msblk, buf, b, offset, length,
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output);
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if (length < 0)
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goto read_failure;
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} else {
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/*
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* Block is uncompressed.
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*/
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int pg_offset = 0;
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void *data = squashfs_first_page(output);
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for (bytes = length; k < b; k++) {
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int in = min(bytes, msblk->devblksize - offset);
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bytes -= in;
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while (in) {
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if (pg_offset == PAGE_CACHE_SIZE) {
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data = squashfs_next_page(output);
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pg_offset = 0;
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}
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avail = min_t(int, in, PAGE_CACHE_SIZE -
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pg_offset);
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memcpy(data + pg_offset, buf[k] + offset,
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avail);
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in -= avail;
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pg_offset += avail;
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offset += avail;
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}
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offset = 0;
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kfree(buf[k]);
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}
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squashfs_finish_page(output);
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}
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kfree(buf);
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return length;
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block_release:
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for (; k < b; k++)
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kfree(buf[k]);
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read_failure:
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ERROR("squashfs_read_data failed to read block 0x%llx\n",
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(unsigned long long) index);
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kfree(buf);
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return -EIO;
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}
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