vt: prevent kernel-infoleak in con_font_get()

font.data may not initialize all memory spaces depending on the implementation
of vc->vc_sw->con_font_get. This may cause info-leak, so to prevent this, it
is safest to modify it to initialize the allocated memory space to 0, and it
generally does not affect the overall performance of the system.

Cc: stable@vger.kernel.org
Reported-by: syzbot+955da2d57931604ee691@syzkaller.appspotmail.com
Fixes: 05e2600c ("VT: Bump font size limitation to 64x128 pixels")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Link: https://lore.kernel.org/r/20241010174619.59662-1-aha310510@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/vt.c

@@ -4726,7 +4726,7 @@ static int con_font_get(struct vc_data *vc, struct console_font_op *op)
 		return -EINVAL;
 
 	if (op->data) {
-		font.data = kvmalloc(max_font_size, GFP_KERNEL);
+		font.data = kvzalloc(max_font_size, GFP_KERNEL);
 		if (!font.data)
 			return -ENOMEM;
 	} else