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().

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#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;

}

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