CVE-2026-68434

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

serial: 8250_mid: Fix NULL function pointer dereference on DNV/ICX-D/SNR platforms

Commit b1b4efea05a5 ("serial: 8250mid: Disable DMA for selected platforms") replaced the dnvboard setup and exit callbacks with PTRIF(false, ...), which evaluates to NULL. However, the three call sites in mid8250probe() and mid8250_remove() unconditionally dereference these function pointers without NULL checks, causing a NULL pointer dereference (kernel oops) on any Denverton (DNV), Ice Lake Xeon D (ICX-D/CDF), or Snowridge (SNR) platform.

Fix this by adding the missing NULL checks before calling the setup and exit callbacks.