detect_form(struct archive_read *a, int *is_form_d)
{
	const char *p;
	ssize_t avail, ravail;
	ssize_t detected_bytes = 0, len, nl;
	int entry_cnt = 0, multiline = 0;
	int form_D = 0;/* The archive is generated by `NetBSD mtree -D'
			* (In this source we call it `form D') . */

	if (is_form_d != NULL)
		*is_form_d = 0;
	p = __archive_read_ahead(a, 1, &avail);
	if (p == NULL)
		return (-1);
	ravail = avail;
	for (;;) {
		len = next_line(a, &p, &avail, &ravail, &nl);
		/* The terminal character of the line should be
		 * a new line character, '\r\n' or '\n'. */
		if (len <= 0 || nl == 0)
			break;
		if (!multiline) {
			/* Leading whitespace is never significant,
			 * ignore it. */
			while (len > 0 && (*p == ' ' || *p == '\t')) {
				++p;
				--avail;
				--len;
			}
			/* Skip comment or empty line. */ 
			if (p[0] == '#' || p[0] == '\n' || p[0] == '\r') {
				p += len;
				avail -= len;
				continue;
			}
		} else {
			/* A continuance line; the terminal
			 * character of previous line was '\' character. */
			if (bid_keyword_list(p, len, 0, 0) <= 0)
				break;
			if (multiline == 1)
				detected_bytes += len;
			if (p[len-nl-1] != '\\') {
				if (multiline == 1 &&
				    ++entry_cnt >= MAX_BID_ENTRY)
					break;
				multiline = 0;
			}
			p += len;
			avail -= len;
			continue;
		}
		if (p[0] != '/') {
			int last_is_path, keywords;

			keywords = bid_entry(p, len, nl, &last_is_path);
			if (keywords >= 0) {
				detected_bytes += len;
				if (form_D == 0) {
					if (last_is_path)
						form_D = 1;
					else if (keywords > 0)
						/* This line is not `form D'. */
						form_D = -1;
				} else if (form_D == 1) {
					if (!last_is_path && keywords > 0)
						/* This this is not `form D'
						 * and We cannot accept mixed
						 * format. */
						break;
				}
				if (!last_is_path && p[len-nl-1] == '\\')
					/* This line continues. */
					multiline = 1;
				else {
					/* We've got plenty of correct lines
					 * to assume that this file is a mtree
					 * format. */
					if (++entry_cnt >= MAX_BID_ENTRY)
						break;
				}
			} else
				break;
		} else if (strncmp(p, "/set", 4) == 0) {
			if (bid_keyword_list(p+4, len-4, 0, 0) <= 0)
				break;
			/* This line continues. */
			if (p[len-nl-1] == '\\')
				multiline = 2;
		} else if (strncmp(p, "/unset", 6) == 0) {
			if (bid_keyword_list(p+6, len-6, 1, 0) <= 0)
				break;
			/* This line continues. */
			if (p[len-nl-1] == '\\')
				multiline = 2;
		} else
			break;

		/* Test next line. */
		p += len;
		avail -= len;
	}
	if (entry_cnt >= MAX_BID_ENTRY || (entry_cnt > 0 && len == 0)) {
		if (is_form_d != NULL) {
			if (form_D == 1)
				*is_form_d = 1;
		}
		return (32);
	}

	return (0);
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.