CVE-2026-64271: Input: touchwin - reset the packet index on every complete packet

In the Linux kernel, the following vulnerability has been resolved:

Input: touchwin - reset the packet index on every complete packet

twinterrupt() accumulates each non-zero serial byte into a fixed three-byte buffer with a running index that is only reset once a full packet has been received and the device's two Y bytes agree:

tw->data[tw->idx++] = data; if (tw->idx == TWLENGTH && tw->data[1] == tw->data[2]) { ... tw->idx = 0; }

The reset is gated on tw->data[1] == tw->data[2], a value the device controls. A malicious, malfunctioning or counterfeit Touchwindow peripheral can stream non-zero bytes whose 2nd and 3rd bytes differ: the index reaches TWLENGTH without the equality holding, is never reset, and keeps growing, so tw->data[tw->idx++] walks off the end of the three-byte array and the rest of the heap-allocated struct tw, one attacker-chosen byte at a time -- an unbounded, device-driven heap out-of-bounds write.

Reset the index on every completed packet and report an event only when the two Y bytes match, like the other serio touchscreen drivers do.