/* SPDX-License-Identifier: GPL-3.0-or-later */
/*
 * read_header.c
 *
 * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
 */
#include "config.h"

#include "internal.h"

static bool is_zero_block(const tar_header_t *hdr)
{
	const unsigned char *ptr = (const unsigned char *)hdr;

	return ptr[0] == '\0' && memcmp(ptr, ptr + 1, sizeof(*hdr) - 1) == 0;
}

static int check_version(const tar_header_t *hdr)
{
	char buffer[sizeof(hdr->magic) + sizeof(hdr->version)];

	memset(buffer, '\0', sizeof(buffer));
	if (memcmp(hdr->magic, buffer, sizeof(hdr->magic)) == 0 &&
	    memcmp(hdr->version, buffer, sizeof(hdr->version)) == 0)
		return ETV_V7_UNIX;

	if (memcmp(hdr->magic, TAR_MAGIC, sizeof(hdr->magic)) == 0 &&
	    memcmp(hdr->version, TAR_VERSION, sizeof(hdr->version)) == 0)
		return ETV_POSIX;

	if (memcmp(hdr->magic, TAR_MAGIC_OLD, sizeof(hdr->magic)) == 0 &&
	    memcmp(hdr->version, TAR_VERSION_OLD, sizeof(hdr->version)) == 0)
		return ETV_PRE_POSIX;

	return ETV_UNKNOWN;
}

static int decode_header(const tar_header_t *hdr, unsigned int set_by_pax,
			 tar_header_decoded_t *out, int version)
{
	size_t len1, len2;
	sqfs_u64 field;

	if (!(set_by_pax & PAX_NAME)) {
		if (hdr->tail.posix.prefix[0] != '\0' &&
		    version == ETV_POSIX) {
			len1 = strnlen(hdr->name, sizeof(hdr->name));
			len2 = strnlen(hdr->tail.posix.prefix,
				       sizeof(hdr->tail.posix.prefix));

			out->name = malloc(len1 + 1 + len2 + 1);

			if (out->name != NULL) {
				memcpy(out->name, hdr->tail.posix.prefix, len2);
				out->name[len2] = '/';
				memcpy(out->name + len2 + 1, hdr->name, len1);
				out->name[len1 + 1 + len2] = '\0';
			}
		} else {
			out->name = strndup(hdr->name, sizeof(hdr->name));
		}

		if (out->name == NULL) {
			perror("decoding filename");
			return -1;
		}
	}

	if (!(set_by_pax & PAX_SIZE)) {
		if (read_number(hdr->size, sizeof(hdr->size), &out->record_size))
			return -1;
	}

	if (!(set_by_pax & PAX_UID)) {
		if (read_number(hdr->uid, sizeof(hdr->uid), &field))
			return -1;
		out->sb.st_uid = field;
	}

	if (!(set_by_pax & PAX_GID)) {
		if (read_number(hdr->gid, sizeof(hdr->gid), &field))
			return -1;
		out->sb.st_gid = field;
	}

	if (!(set_by_pax & PAX_DEV_MAJ)) {
		if (read_number(hdr->devmajor, sizeof(hdr->devmajor), &field))
			return -1;

		out->sb.st_rdev = makedev(field, minor(out->sb.st_rdev));
	}

	if (!(set_by_pax & PAX_DEV_MIN)) {
		if (read_number(hdr->devminor, sizeof(hdr->devminor), &field))
			return -1;

		out->sb.st_rdev = makedev(major(out->sb.st_rdev), field);
	}

	if (!(set_by_pax & PAX_MTIME)) {
		if (read_number(hdr->mtime, sizeof(hdr->mtime), &field))
			return -1;
		if (field & 0x8000000000000000UL) {
			field = ~field + 1;
			out->mtime = -((sqfs_s64)field);
		} else {
			out->mtime = field;
		}
	}

	if (read_octal(hdr->mode, sizeof(hdr->mode), &field))
		return -1;

	out->sb.st_mode = field & 07777;

	if (hdr->typeflag == TAR_TYPE_LINK ||
	    hdr->typeflag == TAR_TYPE_SLINK) {
		if (!(set_by_pax & PAX_SLINK_TARGET)) {
			out->link_target = strndup(hdr->linkname,
						   sizeof(hdr->linkname));
			if (out->link_target == NULL) {
				perror("decoding symlink target");
				return -1;
			}
		}
	}

	out->unknown_record = false;

	switch (hdr->typeflag) {
	case '\0':
	case TAR_TYPE_FILE:
	case TAR_TYPE_GNU_SPARSE:
		out->sb.st_mode |= S_IFREG;
		break;
	case TAR_TYPE_LINK:
		out->is_hard_link = true;
		break;
	case TAR_TYPE_SLINK:
		out->sb.st_mode = S_IFLNK | 0777;
		break;
	case TAR_TYPE_CHARDEV:
		out->sb.st_mode |= S_IFCHR;
		break;
	case TAR_TYPE_BLOCKDEV:
		out->sb.st_mode |= S_IFBLK;
		break;
	case TAR_TYPE_DIR:
		out->sb.st_mode |= S_IFDIR;
		break;
	case TAR_TYPE_FIFO:
		out->sb.st_mode |= S_IFIFO;
		break;
	default:
		out->unknown_record = true;
		break;
	}

	if (sizeof(time_t) * CHAR_BIT < 64) {
		if (out->mtime > (sqfs_s64)INT32_MAX) {
			out->sb.st_mtime = INT32_MAX;
		} else if (out->mtime < (sqfs_s64)INT32_MIN) {
			out->sb.st_mtime = INT32_MIN;
		} else {
			out->sb.st_mtime = out->mtime;
		}
	} else {
		out->sb.st_mtime = out->mtime;
	}
	return 0;
}

int read_header(FILE *fp, tar_header_decoded_t *out)
{
	unsigned int set_by_pax = 0;
	bool prev_was_zero = false;
	sqfs_u64 pax_size;
	tar_header_t hdr;
	int version;

	memset(out, 0, sizeof(*out));

	for (;;) {
		if (read_retry("reading tar header", fp, &hdr, sizeof(hdr)))
			goto fail;

		if (is_zero_block(&hdr)) {
			if (prev_was_zero)
				goto out_eof;
			prev_was_zero = true;
			continue;
		}

		prev_was_zero = false;
		version = check_version(&hdr);

		if (version == ETV_UNKNOWN)
			goto fail_magic;

		if (!is_checksum_valid(&hdr))
			goto fail_chksum;

		switch (hdr.typeflag) {
		case TAR_TYPE_GNU_SLINK:
			if (read_number(hdr.size, sizeof(hdr.size), &pax_size))
				goto fail;
			if (pax_size < 1 || pax_size > TAR_MAX_SYMLINK_LEN)
				goto fail_slink_len;
			free(out->link_target);
			out->link_target = record_to_memory(fp, pax_size);
			if (out->link_target == NULL)
				goto fail;
			set_by_pax |= PAX_SLINK_TARGET;
			continue;
		case TAR_TYPE_GNU_PATH:
			if (read_number(hdr.size, sizeof(hdr.size), &pax_size))
				goto fail;
			if (pax_size < 1 || pax_size > TAR_MAX_PATH_LEN)
				goto fail_path_len;
			free(out->name);
			out->name = record_to_memory(fp, pax_size);
			if (out->name == NULL)
				goto fail;
			set_by_pax |= PAX_NAME;
			continue;
		case TAR_TYPE_PAX_GLOBAL:
			if (read_number(hdr.size, sizeof(hdr.size), &pax_size))
				goto fail;
			skip_entry(fp, pax_size);
			continue;
		case TAR_TYPE_PAX:
			clear_header(out);
			if (read_number(hdr.size, sizeof(hdr.size), &pax_size))
				goto fail;
			if (pax_size < 1 || pax_size > TAR_MAX_PAX_LEN)
				goto fail_pax_len;
			set_by_pax = 0;
			if (read_pax_header(fp, pax_size, &set_by_pax, out))
				goto fail;
			continue;
		case TAR_TYPE_GNU_SPARSE:
			free_sparse_list(out->sparse);
			out->sparse = read_gnu_old_sparse(fp, &hdr);
			if (out->sparse == NULL)
				goto fail;
			if (read_number(hdr.tail.gnu.realsize,
					sizeof(hdr.tail.gnu.realsize),
					&out->actual_size))
				goto fail;
			break;
		default:
			break;
		}
		break;
	}

	if (decode_header(&hdr, set_by_pax, out, version))
		goto fail;

	if (set_by_pax & PAX_SPARSE_GNU_1_X) {
		free_sparse_list(out->sparse);
		out->sparse = read_gnu_new_sparse(fp, out);
		if (out->sparse == NULL)
			goto fail;
	}

	if (out->sparse != NULL) {
		out->sb.st_size = out->actual_size;
	} else {
		out->sb.st_size = out->record_size;
		out->actual_size = out->record_size;
	}
	return 0;
out_eof:
	clear_header(out);
	return 1;
fail_slink_len:
	fprintf(stderr, "rejecting GNU symlink header with size %lu\n",
		(unsigned long)pax_size);
	goto fail;
fail_path_len:
	fprintf(stderr, "rejecting GNU long path header with size %lu\n",
		(unsigned long)pax_size);
	goto fail;
fail_pax_len:
	fprintf(stderr, "rejecting PAX header with size %lu\n",
		(unsigned long)pax_size);
	goto fail;
fail_magic:
	fputs("input is not a ustar tar archive!\n", stderr);
	goto fail;
fail_chksum:
	fputs("invalid tar header checksum!\n", stderr);
	goto fail;
fail:
	clear_header(out);
	return -1;
}