tty: make FONTX ioctl use the tty pointer they were actually passed

mainline inclusion
from mainline-v5.10-rc3
commit 90bfdeef
category: bugfix
bugzilla: NA
CVE: CVE-2020-25668

--------------------------------

Some of the font tty ioctl's always used the current foreground VC for
their operations.  Don't do that then.

This fixes a data race on fg_console.

Side note: both Michael Ellerman and Jiri Slaby point out that all these
ioctls are deprecated, and should probably have been removed long ago,
and everything seems to be using the KDFONTOP ioctl instead.

In fact, Michael points out that it looks like busybox's loadfont
program seems to have switched over to using KDFONTOP exactly _because_
of this bug (ahem.. 12 years ago ;-).
Reported-by: NMinh Yuan <yuanmingbuaa@gmail.com>
Acked-by: NMichael Ellerman <mpe@ellerman.id.au>
Acked-by: NJiri Slaby <jirislaby@kernel.org>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Conflicts:
  drivers/tty/vt/vt_ioctl.c
[yyl: There is no vt_io_fontreset(), change the vc_cons to vc in do_fontx_ioctl()]
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/tty/vt/vt_ioctl.c

@@ -244,7 +244,7 @@ int vt_waitactive(int n)
 
 
 static inline int 
-do_fontx_ioctl(int cmd, struct consolefontdesc __user *user_cfd, int perm, struct console_font_op *op)
+do_fontx_ioctl(struct vc_data *vc, int cmd, struct consolefontdesc __user *user_cfd, int perm, struct console_font_op *op)
 {
 	struct consolefontdesc cfdarg;
 	int i;
@@ -262,15 +262,16 @@ do_fontx_ioctl(int cmd, struct consolefontdesc __user *user_cfd, int perm, struc
 		op->height = cfdarg.charheight;
 		op->charcount = cfdarg.charcount;
 		op->data = cfdarg.chardata;
-		return con_font_op(vc_cons[fg_console].d, op);
-	case GIO_FONTX: {
+		return con_font_op(vc, op);
+
+	case GIO_FONTX:
 		op->op = KD_FONT_OP_GET;
 		op->flags = KD_FONT_FLAG_OLD;
 		op->width = 8;
 		op->height = cfdarg.charheight;
 		op->charcount = cfdarg.charcount;
 		op->data = cfdarg.chardata;
-		i = con_font_op(vc_cons[fg_console].d, op);
+		i = con_font_op(vc, op);
 		if (i)
 			return i;
 		cfdarg.charheight = op->height;
@@ -279,7 +280,6 @@ do_fontx_ioctl(int cmd, struct consolefontdesc __user *user_cfd, int perm, struc
 			return -EFAULT;
 		return 0;
 	}
-	}
 	return -EINVAL;
 }
 
@@ -914,7 +914,7 @@ int vt_ioctl(struct tty_struct *tty,
 		op.height = 0;
 		op.charcount = 256;
 		op.data = up;
-		ret = con_font_op(vc_cons[fg_console].d, &op);
+		ret = con_font_op(vc, &op);
 		break;
 	}
 
@@ -925,7 +925,7 @@ int vt_ioctl(struct tty_struct *tty,
 		op.height = 32;
 		op.charcount = 256;
 		op.data = up;
-		ret = con_font_op(vc_cons[fg_console].d, &op);
+		ret = con_font_op(vc, &op);
 		break;
 	}
 
@@ -942,7 +942,7 @@ int vt_ioctl(struct tty_struct *tty,
 
 	case PIO_FONTX:
 	case GIO_FONTX:
-		ret = do_fontx_ioctl(cmd, up, perm, &op);
+		ret = do_fontx_ioctl(vc, cmd, up, perm, &op);
 		break;
 
 	case PIO_FONTRESET:
@@ -959,11 +959,11 @@ int vt_ioctl(struct tty_struct *tty,
 		{
 		op.op = KD_FONT_OP_SET_DEFAULT;
 		op.data = NULL;
-		ret = con_font_op(vc_cons[fg_console].d, &op);
+		ret = con_font_op(vc, &op);
 		if (ret)
 			break;
 		console_lock();
-		con_set_default_unimap(vc_cons[fg_console].d);
+		con_set_default_unimap(vc);
 		console_unlock();
 		break;
 		}
@@ -1090,7 +1090,8 @@ struct compat_consolefontdesc {
 };
 
 static inline int
-compat_fontx_ioctl(int cmd, struct compat_consolefontdesc __user *user_cfd,
+compat_fontx_ioctl(struct vc_data *vc, int cmd,
+		   struct compat_consolefontdesc __user *user_cfd,
 		   int perm, struct console_font_op *op)
 {
 	struct compat_consolefontdesc cfdarg;
@@ -1109,7 +1110,8 @@ compat_fontx_ioctl(int cmd, struct compat_consolefontdesc __user *user_cfd,
 		op->height = cfdarg.charheight;
 		op->charcount = cfdarg.charcount;
 		op->data = compat_ptr(cfdarg.chardata);
-		return con_font_op(vc_cons[fg_console].d, op);
+		return con_font_op(vc, op);
+
 	case GIO_FONTX:
 		op->op = KD_FONT_OP_GET;
 		op->flags = KD_FONT_FLAG_OLD;
@@ -1117,7 +1119,7 @@ compat_fontx_ioctl(int cmd, struct compat_consolefontdesc __user *user_cfd,
 		op->height = cfdarg.charheight;
 		op->charcount = cfdarg.charcount;
 		op->data = compat_ptr(cfdarg.chardata);
-		i = con_font_op(vc_cons[fg_console].d, op);
+		i = con_font_op(vc, op);
 		if (i)
 			return i;
 		cfdarg.charheight = op->height;
@@ -1208,7 +1210,7 @@ long vt_compat_ioctl(struct tty_struct *tty,
 	 */
 	case PIO_FONTX:
 	case GIO_FONTX:
-		ret = compat_fontx_ioctl(cmd, up, perm, &op);
+		ret = compat_fontx_ioctl(vc, cmd, up, perm, &op);
 		break;
 
 	case KDFONTOP: