src/cpio.c

/*
 * Copyright 2018 The Hafnium Authors.
 *
 * Use of this source code is governed by a BSD-style
 * license that can be found in the LICENSE file or at
 * https://opensource.org/licenses/BSD-3-Clause.
 */

#include "hf/cpio.h"

#include <stdint.h>

#include "hf/dlog.h"
#include "hf/std.h"

#define CPIO_OLD_BINARY_FORMAT_MAGIC 070707

#pragma pack(push, 1)
struct cpio_header {
	uint16_t magic;
	uint16_t dev;
	uint16_t ino;
	uint16_t mode;
	uint16_t uid;
	uint16_t gid;
	uint16_t nlink;
	uint16_t rdev;
	uint16_t mtime[2];
	uint16_t namesize;
	uint16_t filesize[2];
};
#pragma pack(pop)

/**
 * Retrieves the next file stored in the cpio archive stored in the cpio, and
 * advances the iterator such that another call to this function would return
 * the following file.
 */
static bool cpio_next(struct memiter *iter, const char **name,
		      const void **contents, size_t *size)
{
	static const char trailer[] = "TRAILER!!!";
	size_t len;
	struct memiter lit;
	const struct cpio_header *h;

	if (!iter) {
		return false;
	}

	lit = *iter;

	h = (const struct cpio_header *)lit.next;
	if (!h) {
		return false;
	}

	if (!memiter_advance(&lit, sizeof(struct cpio_header))) {
		return false;
	}

	if (h->magic != CPIO_OLD_BINARY_FORMAT_MAGIC) {
		dlog_error("cpio: only old binary format is supported\n");
		return false;
	}

	*name = lit.next;

	len = (h->namesize + 1) & ~1;
	if (!memiter_advance(&lit, len)) {
		return false;
	}

	/* previous memiter_advance checks for boundaries */
	if (h->namesize == 0U || (*name)[h->namesize - 1] != '\0') {
		return false;
	}

	*contents = lit.next;

	len = (size_t)h->filesize[0] << 16 | h->filesize[1];
	if (!memiter_advance(&lit, (len + 1) & ~1)) {
		return false;
	}

	/* Stop enumerating files when we hit the end marker. */
	if (!strncmp(*name, trailer, sizeof(trailer))) {
		return false;
	}

	*size = len;
	*iter = lit;

	return true;
}

/**
 * Looks for a file in the given cpio archive. The file, if found, is returned
 * in the "it" argument.
 */
bool cpio_get_file(const struct memiter *cpio, const struct string *name,
		   struct memiter *it)
{
	const char *fname;
	const void *fcontents;
	size_t fsize;
	struct memiter iter = *cpio;

	while (cpio_next(&iter, &fname, &fcontents, &fsize)) {
		if (!strncmp(fname, string_data(name), STRING_MAX_SIZE)) {
			memiter_init(it, fcontents, fsize);
			return true;
		}
	}

	return false;
}