int expread(off_t a, char *buf, size_t len, CLIENT *client) {
	off_t rdlen, offset;
	off_t mapcnt, mapl, maph, pagestart;

	if (!(client->server->flags & F_COPYONWRITE))
		return(rawexpread_fully(a, buf, len, client));
	DEBUG3("Asked to read %d bytes at %llu.\n", len, (unsigned long long)a);

	mapl=a/DIFFPAGESIZE; maph=(a+len-1)/DIFFPAGESIZE;

	for (mapcnt=mapl;mapcnt<=maph;mapcnt++) {
		pagestart=mapcnt*DIFFPAGESIZE;
		offset=a-pagestart;
		rdlen=(0<DIFFPAGESIZE-offset && len<(size_t)(DIFFPAGESIZE-offset)) ?
			len : (size_t)DIFFPAGESIZE-offset;
		if (client->difmap[mapcnt]!=(u32)(-1)) { /* the block is already there */
			DEBUG3("Page %llu is at %lu\n", (unsigned long long)mapcnt,
			       (unsigned long)(client->difmap[mapcnt]));
			myseek(client->difffile, client->difmap[mapcnt]*DIFFPAGESIZE+offset);
			if (read(client->difffile, buf, rdlen) != rdlen) return -1;
		} else { /* the block is not there */
			DEBUG2("Page %llu is not here, we read the original one\n",
			       (unsigned long long)mapcnt);
			if(rawexpread_fully(a, buf, rdlen, client)) return -1;
		}
		len-=rdlen; a+=rdlen; buf+=rdlen;
	}
	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.