CVE-2026-64483: ALSA: firewire: isight: bound the sample count to the packet payload

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

ALSA: firewire: isight: bound the sample count to the packet payload

isightpacket() takes the frame count from the device iso packet and checks it only against the device claimed iso length.

count = be32tocpu(payload->samplecount); if (likely(count <= (length - 16) / 4)) isightsamples(isight, payload->samples, count);

length is the iso header datalength. It can be up to 0xffff. So the gate allows a count up to about 16379. isightsamples() then copies count frames out of payload->samples into the PCM DMA buffer.

payload->samples holds only 2 MAXFRAMESPERPACKET values. The device multiplexes two samples per frame. A count past MAXFRAMESPERPACKET reads past the payload. A count past the buffer size writes past runtime->dmaarea. The smallest PCM buffer is larger than MAXFRAMESPERPACKET. Bounding the count to MAXFRAMESPERPACKET keeps both the read and the write in range.

A malicious or faulty Apple iSight on the FireWire bus reaches this during a normal capture.

Add the MAXFRAMESPERPACKET bound to the gate.