vt: save/restore unicode screen buffer for alternate screen

The alternate screen support added by commit 23743ba ("vt: add
support for smput/rmput escape codes") only saves and restores the
regular screen buffer (vc_origin), but completely ignores the corresponding
unicode screen buffer (vc_uni_lines) creating a messed-up display.

Add vc_saved_uni_lines to save the unicode screen buffer when entering
the alternate screen, and restore it when leaving. Also ensure proper
cleanup in reset_terminal() and vc_deallocate().

Fixes: 23743ba ("vt: add support for smput/rmput escape codes")
Cc: stable <[email protected]>
Signed-off-by: Nicolas Pitre <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: npitre

drivers/tty/vt/vt.c

@@ -1339,6 +1339,8 @@ struct vc_data *vc_deallocate(unsigned int currcons)
 			kfree(vc->vc_saved_screen);
 			vc->vc_saved_screen = NULL;
 		}
+		vc_uniscr_free(vc->vc_saved_uni_lines);
+		vc->vc_saved_uni_lines = NULL;
 	}
 	return vc;
 }
@@ -1884,6 +1886,8 @@ static void enter_alt_screen(struct vc_data *vc)
 	vc->vc_saved_screen = kmemdup((u16 *)vc->vc_origin, size, GFP_KERNEL);
 	if (vc->vc_saved_screen == NULL)
 		return;
+	vc->vc_saved_uni_lines = vc->vc_uni_lines;
+	vc->vc_uni_lines = NULL;
 	vc->vc_saved_rows = vc->vc_rows;
 	vc->vc_saved_cols = vc->vc_cols;
 	save_cur(vc);
@@ -1905,6 +1909,8 @@ static void leave_alt_screen(struct vc_data *vc)
 		dest = ((u16 *)vc->vc_origin) + r * vc->vc_cols;
 		memcpy(dest, src, 2 * cols);
 	}
+	vc_uniscr_set(vc, vc->vc_saved_uni_lines);
+	vc->vc_saved_uni_lines = NULL;
 	restore_cur(vc);
 	/* Update the entire screen */
 	if (con_should_update(vc))
@@ -2227,6 +2233,8 @@ static void reset_terminal(struct vc_data *vc, int do_clear)
 	if (vc->vc_saved_screen != NULL) {
 		kfree(vc->vc_saved_screen);
 		vc->vc_saved_screen = NULL;
+		vc_uniscr_free(vc->vc_saved_uni_lines);
+		vc->vc_saved_uni_lines = NULL;
 		vc->vc_saved_rows = 0;
 		vc->vc_saved_cols = 0;
 	}

include/linux/console_struct.h

@@ -160,6 +160,7 @@ struct vc_data {
 	struct uni_pagedict **uni_pagedict_loc; /* [!] Location of uni_pagedict variable for this console */
 	u32 **vc_uni_lines;			/* unicode screen content */
 	u16		*vc_saved_screen;
+	u32		**vc_saved_uni_lines;
 	unsigned int	vc_saved_cols;
 	unsigned int	vc_saved_rows;
 	/* additional information is in vt_kern.h */