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

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: Minh Yuan <yuanmingbuaa@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Jiri Slaby <jirislaby@kernel.org>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/tty/vt/vt_ioctl.c

@@ -484,7 +484,7 @@ static int vt_k_ioctl(struct tty_struct *tty, unsigned int cmd,
 	return 0;
 }
 
-static inline int do_fontx_ioctl(int cmd,
+static inline int do_fontx_ioctl(struct vc_data *vc, int cmd,
 		struct consolefontdesc __user *user_cfd,
 		struct console_font_op *op)
 {
@@ -502,15 +502,16 @@ static inline int do_fontx_ioctl(int cmd,
 		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;
@@ -518,12 +519,11 @@ static inline int do_fontx_ioctl(int cmd,
 		if (copy_to_user(user_cfd, &cfdarg, sizeof(struct consolefontdesc)))
 			return -EFAULT;
 		return 0;
-		}
 	}
 	return -EINVAL;
 }
 
-static int vt_io_fontreset(struct console_font_op *op)
+static int vt_io_fontreset(struct vc_data *vc, struct console_font_op *op)
 {
 	int ret;
 
@@ -537,12 +537,12 @@ static int vt_io_fontreset(struct console_font_op *op)
 
 	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)
 		return ret;
 
 	console_lock();
-	con_set_default_unimap(vc_cons[fg_console].d);
+	con_set_default_unimap(vc);
 	console_unlock();
 
 	return 0;
@@ -584,7 +584,7 @@ static int vt_io_ioctl(struct vc_data *vc, unsigned int cmd, void __user *up,
 		op.height = 0;
 		op.charcount = 256;
 		op.data = up;
-		return con_font_op(vc_cons[fg_console].d, &op);
+		return con_font_op(vc, &op);
 
 	case GIO_FONT:
 		op.op = KD_FONT_OP_GET;
@@ -593,7 +593,7 @@ static int vt_io_ioctl(struct vc_data *vc, unsigned int cmd, void __user *up,
 		op.height = 32;
 		op.charcount = 256;
 		op.data = up;
-		return con_font_op(vc_cons[fg_console].d, &op);
+		return con_font_op(vc, &op);
 
 	case PIO_CMAP:
                 if (!perm)
@@ -609,13 +609,13 @@ static int vt_io_ioctl(struct vc_data *vc, unsigned int cmd, void __user *up,
 
 		fallthrough;
 	case GIO_FONTX:
-		return do_fontx_ioctl(cmd, up, &op);
+		return do_fontx_ioctl(vc, cmd, up, &op);
 
 	case PIO_FONTRESET:
 		if (!perm)
 			return -EPERM;
 
-		return vt_io_fontreset(&op);
+		return vt_io_fontreset(vc, &op);
 
 	case PIO_SCRNMAP:
 		if (!perm)
@@ -1066,8 +1066,9 @@ struct compat_consolefontdesc {
 };
 
 static inline int
-compat_fontx_ioctl(int cmd, struct compat_consolefontdesc __user *user_cfd,
-			 int perm, struct console_font_op *op)
+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;
 	int i;
@@ -1085,7 +1086,8 @@ 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;
@@ -1093,7 +1095,7 @@ 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;
@@ -1183,7 +1185,7 @@ long vt_compat_ioctl(struct tty_struct *tty,
 	 */
 	case PIO_FONTX:
 	case GIO_FONTX:
-		return compat_fontx_ioctl(cmd, up, perm, &op);
+		return compat_fontx_ioctl(vc, cmd, up, perm, &op);
 
 	case KDFONTOP:
 		return compat_kdfontop_ioctl(up, perm, &op, vc);