tty: vt: initialize unicode screen buffer

In the Linux kernel, the following vulnerability has been resolved: tty: vt: initialize unicode screen buffer syzbot reports kernel infoleak at vcs_read() [1], for buffer can be read immediately after resize operation. Initialize buffer using kzalloc(). ---------- #include <fcntl.h> #include <unistd.h> #include <sys/ioctl.h> #include <linux/fb.h> int main(int argc, char *argv[]) { struct fb_var_screeninfo var = { }; const int fb_fd = open("/dev/fb0", 3); ioctl(fb_fd, FBIOGET_VSCREENINFO, &var); var.yres = 0x21; ioctl(fb_fd, FBIOPUT_VSCREENINFO, &var); return read(open("/dev/vcsu", O_RDONLY), &var, sizeof(var)) == -1; } ----------