[PATCH 4.9 54/78] vt_ioctl: change VT_RESIZEX ioctl to check for error return from vc_resize()

[Greg Kroah-Hartman]

From: George Kennedy <george.kennedy@xxxxxxxxxx>

commit bc5269ca765057a1b762e79a1cfd267cd7bf1c46 upstream.

vc_resize() can return with an error after failure. Change VT_RESIZEX ioctl
to save struct vc_data values that are modified and restore the original
values in case of error.

Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Reported-by: syzbot+38a3699c7eaf165b97a6@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/1596213192-6635-2-git-send-email-george.kennedy@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/vt/vt_ioctl.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/tty/vt/vt_ioctl.c
+++ b/drivers/tty/vt/vt_ioctl.c
@@ -896,12 +896,22 @@ int vt_ioctl(struct tty_struct *tty,
 			console_lock();
 			vcp = vc_cons[i].d;
 			if (vcp) {
+				int ret;
+				int save_scan_lines = vcp->vc_scan_lines;
+				int save_font_height = vcp->vc_font.height;
+
 				if (v.v_vlin)
 					vcp->vc_scan_lines = v.v_vlin;
 				if (v.v_clin)
 					vcp->vc_font.height = v.v_clin;
 				vcp->vc_resize_user = 1;
-				vc_resize(vcp, v.v_cols, v.v_rows);
+				ret = vc_resize(vcp, v.v_cols, v.v_rows);
+				if (ret) {
+					vcp->vc_scan_lines = save_scan_lines;
+					vcp->vc_font.height = save_font_height;
+					console_unlock();
+					return ret;
+				}
 			}
 			console_unlock();
 		}