[PATCH 5.4 88/92] vcs: prevent write access to vcsu devices

[Greg Kroah-Hartman]

From: Nicolas Pitre <nico@xxxxxxxxxxx>

commit 0c9acb1af77a3cb8707e43f45b72c95266903cee upstream.

Commit d21b0be246bf ("vt: introduce unicode mode for /dev/vcs") guarded
against using devices containing attributes as this is not yet
implemented. It however failed to guard against writes to any devices
as this is also unimplemented.

Reported-by: Or Cohen <orcohen@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Nicolas Pitre <npitre@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.19+
Cc: Jiri Slaby <jslaby@xxxxxxxx>
Fixes: d21b0be246bf ("vt: introduce unicode mode for /dev/vcs")
Link: https://lore.kernel.org/r/nycvar.YSQ.7.76.1911051030580.30289@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/vt/vc_screen.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -456,6 +456,9 @@ vcs_write(struct file *file, const char
 	size_t ret;
 	char *con_buf;
 
+	if (use_unicode(inode))
+		return -EOPNOTSUPP;
+
 	con_buf = (char *) __get_free_page(GFP_KERNEL);
 	if (!con_buf)
 		return -ENOMEM;