CVE-2026-89818

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

drm/amdgpu/vcn: fix integer overflow in dec_msg buffer count check

If the supplied msg[2] (num_buffers) is 0x3FFFFFFF, the expression
6 + num_buffers * 4 wraps to 2 and the bounds check passes, letting
the parser loop far past the end of the message BO. Triggering it
additionally requires a ~4GiB mapping so that msg[1] survives the
earlier "header does not fit in BO" check.

Rewrite the test in division form, which is overflow-free by
construction. Also update the message to reflect that msg is invalid.