DF-5306 baseline run (unpatched /usr/src/sys/bus/u4b/uvc/uvc_drv.c),
verbatim console (kldload + `sysctl hw.uvcharness=2`):

HARNESS DF-5306: parse_ctrl ret=0 sc.data=0 (expected NULL)
HARNESS DF-5306: calling real uvc_drv_init_video(sc, ctrl, NULL): expect NULL-deref panic at uvc_drv.c:1513 (data->num_altsetting)
Fatal user address access from kernel mode from sysctl at ffffffff82605a1b


Fatal trap 12: page fault while in kernel mode
cpuid = 1; lapic id = 1
fault virtual address	= 0xa
fault code		= supervisor read data, page not present
instruction pointer	= 0x8:0xffffffff82605a1b
stack pointer	        = 0x10:0xfffff8011844f6d8
frame pointer		= 0x10:0xfffff8011844f798
code segment		= base 0x0, limit 0xfffff, type 0x1b
			= DPL 0, pres 1, long 0, def32 0, gran 1
processor eflags	= interrupt enabled, resume, IOPL = 0
current process		= 1213
current thread          = pri 6
kernel: type 12 trap, code=0

CPU1 stopping CPUs: 0x0000003d
 stopped
Stopped at      sysctl_harness+0x30b:   cmpb    $0x1,0xa(%r9)
db>

(vm.sh status -> down; full serial log captured in panic.txt)