CVE-2026-72403: ALSA: FCP: Fix NULL pointer dereference in interface lookup

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

ALSA: FCP: Fix NULL pointer dereference in interface lookup

A malformed USB device can provide a vendor-specific interface without any endpoint descriptors. fcpfindfcinterface() currently selects the first vendor-specific interface and reads endpoint 0 from it, without checking whether the interface actually has any endpoints.

When bNumEndpoints is zero, no endpoint array is allocated for the parsed alternate setting, so getendpoint(..., 0) yields an invalid endpoint descriptor pointer. Dereferencing it through usbendpointnum() then triggers a NULL pointer dereference.

Skip vendor-specific interfaces that do not have any endpoints.