archive_read_format_7zip_read_header(struct archive_read *a,
	struct archive_entry *entry)
{
	struct _7zip *zip = (struct _7zip *)a->format->data;
	struct _7zip_entry *zip_entry;
	int r, ret = ARCHIVE_OK;
	struct _7z_folder *folder = 0;
	uint64_t fidx = 0;

	/*
	 * It should be sufficient to call archive_read_next_header() for
	 * a reader to determine if an entry is encrypted or not. If the
	 * encryption of an entry is only detectable when calling
	 * archive_read_data(), so be it. We'll do the same check there
	 * as well.
	 */
	if (zip->has_encrypted_entries == ARCHIVE_READ_FORMAT_ENCRYPTION_DONT_KNOW) {
		zip->has_encrypted_entries = 0;
	}

	a->archive.archive_format = ARCHIVE_FORMAT_7ZIP;
	if (a->archive.archive_format_name == NULL)
		a->archive.archive_format_name = "7-Zip";

	if (zip->entries == NULL) {
		struct _7z_header_info header;

		memset(&header, 0, sizeof(header));
		r = slurp_central_directory(a, zip, &header);
		free_Header(&header);
		if (r != ARCHIVE_OK)
			return (r);
		zip->entries_remaining = (size_t)zip->numFiles;
		zip->entry = zip->entries;
	} else {
		++zip->entry;
	}
	zip_entry = zip->entry;

	if (zip->entries_remaining <= 0 || zip_entry == NULL)
		return ARCHIVE_EOF;
	--zip->entries_remaining;

	zip->entry_offset = 0;
	zip->end_of_entry = 0;
	zip->entry_crc32 = crc32(0, NULL, 0);

	/* Setup a string conversion for a filename. */
	if (zip->sconv == NULL) {
		zip->sconv = archive_string_conversion_from_charset(
		    &a->archive, "UTF-16LE", 1);
		if (zip->sconv == NULL)
			return (ARCHIVE_FATAL);
	}

	/* Figure out if the entry is encrypted by looking at the folder
	   that is associated to the current 7zip entry. If the folder
	   has a coder with a _7Z_CRYPTO codec then the folder is encrypted.
	   Hence the entry must also be encrypted. */
	if (zip_entry && zip_entry->folderIndex < zip->si.ci.numFolders) {
		folder = &(zip->si.ci.folders[zip_entry->folderIndex]);
		for (fidx=0; folder && fidx<folder->numCoders; fidx++) {
			switch(folder->coders[fidx].codec) {
				case _7Z_CRYPTO_MAIN_ZIP:
				case _7Z_CRYPTO_RAR_29:
				case _7Z_CRYPTO_AES_256_SHA_256: {
					archive_entry_set_is_data_encrypted(entry, 1);
					zip->has_encrypted_entries = 1;
					break;
				}
			}
		}
	}

	/* Now that we've checked for encryption, if there were still no
	 * encrypted entries found we can say for sure that there are none.
	 */
	if (zip->has_encrypted_entries == ARCHIVE_READ_FORMAT_ENCRYPTION_DONT_KNOW) {
		zip->has_encrypted_entries = 0;
	}

	if (archive_entry_copy_pathname_l(entry,
	    (const char *)zip_entry->utf16name,
	    zip_entry->name_len, zip->sconv) != 0) {
		if (errno == ENOMEM) {
			archive_set_error(&a->archive, ENOMEM,
			    "Can't allocate memory for Pathname");
			return (ARCHIVE_FATAL);
		}
		archive_set_error(&a->archive,
		    ARCHIVE_ERRNO_FILE_FORMAT,
		    "Pathname cannot be converted "
		    "from %s to current locale.",
		    archive_string_conversion_charset_name(zip->sconv));
		ret = ARCHIVE_WARN;
	}

	/* Populate some additional entry fields: */
	archive_entry_set_mode(entry, zip_entry->mode);
	if (zip_entry->flg & MTIME_IS_SET)
		archive_entry_set_mtime(entry, zip_entry->mtime,
			zip_entry->mtime_ns);
	if (zip_entry->flg & CTIME_IS_SET)
		archive_entry_set_ctime(entry, zip_entry->ctime,
		    zip_entry->ctime_ns);
	if (zip_entry->flg & ATIME_IS_SET)
		archive_entry_set_atime(entry, zip_entry->atime,
		    zip_entry->atime_ns);
	if (zip_entry->ssIndex != (uint32_t)-1) {
		zip->entry_bytes_remaining =
		    zip->si.ss.unpackSizes[zip_entry->ssIndex];
		archive_entry_set_size(entry, zip->entry_bytes_remaining);
	} else {
		zip->entry_bytes_remaining = 0;
		archive_entry_set_size(entry, 0);
	}

	/* If there's no body, force read_data() to return EOF immediately. */
	if (zip->entry_bytes_remaining < 1)
		zip->end_of_entry = 1;

	if ((zip_entry->mode & AE_IFMT) == AE_IFLNK) {
		unsigned char *symname = NULL;
		size_t symsize = 0;

		/*
		 * Symbolic-name is recorded as its contents. We have to
		 * read the contents at this time.
		 */
		while (zip->entry_bytes_remaining > 0) {
			const void *buff;
			unsigned char *mem;
			size_t size;
			int64_t offset;

			r = archive_read_format_7zip_read_data(a, &buff,
				&size, &offset);
			if (r < ARCHIVE_WARN) {
				free(symname);
				return (r);
			}
			mem = realloc(symname, symsize + size + 1);
			if (mem == NULL) {
				free(symname);
				archive_set_error(&a->archive, ENOMEM,
				    "Can't allocate memory for Symname");
				return (ARCHIVE_FATAL);
			}
			symname = mem;
			memcpy(symname+symsize, buff, size);
			symsize += size;
		}
		if (symsize == 0) {
			/* If there is no synname, handle it as a regular
			 * file. */
			zip_entry->mode &= ~AE_IFMT;
			zip_entry->mode |= AE_IFREG;
			archive_entry_set_mode(entry, zip_entry->mode);
		} else {
			symname[symsize] = '\0';
			archive_entry_copy_symlink(entry,
			    (const char *)symname);
		}
		free(symname);
		archive_entry_set_size(entry, 0);
	}

	/* Set up a more descriptive format name. */
	sprintf(zip->format_name, "7-Zip");
	a->archive.archive_format_name = zip->format_name;

	return (ret);
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.