static int read_entry(
	git_index_entry **out,
	size_t *out_size,
	git_index *index,
	const void *buffer,
	size_t buffer_size,
	const char *last)
{
	size_t path_length, entry_size;
	const char *path_ptr;
	struct entry_short source;
	git_index_entry entry = {{0}};
	bool compressed = index->version >= INDEX_VERSION_NUMBER_COMP;
	char *tmp_path = NULL;

	if (INDEX_FOOTER_SIZE + minimal_entry_size > buffer_size)
		return -1;

	/* buffer is not guaranteed to be aligned */
	memcpy(&source, buffer, sizeof(struct entry_short));

	entry.ctime.seconds = (git_time_t)ntohl(source.ctime.seconds);
	entry.ctime.nanoseconds = ntohl(source.ctime.nanoseconds);
	entry.mtime.seconds = (git_time_t)ntohl(source.mtime.seconds);
	entry.mtime.nanoseconds = ntohl(source.mtime.nanoseconds);
	entry.dev = ntohl(source.dev);
	entry.ino = ntohl(source.ino);
	entry.mode = ntohl(source.mode);
	entry.uid = ntohl(source.uid);
	entry.gid = ntohl(source.gid);
	entry.file_size = ntohl(source.file_size);
	git_oid_cpy(&entry.id, &source.oid);
	entry.flags = ntohs(source.flags);

	if (entry.flags & GIT_IDXENTRY_EXTENDED) {
		uint16_t flags_raw;
		size_t flags_offset;

		flags_offset = offsetof(struct entry_long, flags_extended);
		memcpy(&flags_raw, (const char *) buffer + flags_offset,
			sizeof(flags_raw));
		flags_raw = ntohs(flags_raw);

		memcpy(&entry.flags_extended, &flags_raw, sizeof(flags_raw));
		path_ptr = (const char *) buffer + offsetof(struct entry_long, path);
	} else
		path_ptr = (const char *) buffer + offsetof(struct entry_short, path);

	if (!compressed) {
		path_length = entry.flags & GIT_IDXENTRY_NAMEMASK;

		/* if this is a very long string, we must find its
		 * real length without overflowing */
		if (path_length == 0xFFF) {
			const char *path_end;

			path_end = memchr(path_ptr, '\0', buffer_size);
			if (path_end == NULL)
				return -1;

			path_length = path_end - path_ptr;
		}

		entry_size = index_entry_size(path_length, 0, entry.flags);
		entry.path = (char *)path_ptr;
	} else {
		size_t varint_len, last_len, prefix_len, suffix_len, path_len;
		uintmax_t strip_len;

		strip_len = git_decode_varint((const unsigned char *)path_ptr, &varint_len);
		last_len = strlen(last);

		if (varint_len == 0 || last_len < strip_len)
			return index_error_invalid("incorrect prefix length");

		prefix_len = last_len - strip_len;
		suffix_len = strlen(path_ptr + varint_len);
 
 		GITERR_CHECK_ALLOC_ADD(&path_len, prefix_len, suffix_len);
 		GITERR_CHECK_ALLOC_ADD(&path_len, path_len, 1);
 		tmp_path = git__malloc(path_len);
 		GITERR_CHECK_ALLOC(tmp_path);
 
		memcpy(tmp_path, last, prefix_len);
		memcpy(tmp_path + prefix_len, path_ptr + varint_len, suffix_len + 1);
		entry_size = index_entry_size(suffix_len, varint_len, entry.flags);
		entry.path = tmp_path;
	}

	if (entry_size == 0)
		return -1;

	if (INDEX_FOOTER_SIZE + entry_size > buffer_size)
		return -1;

	if (index_entry_dup(out, index, &entry) < 0) {
		git__free(tmp_path);
		return -1;
	}

	git__free(tmp_path);
	*out_size = entry_size;
	return 0;
}

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.