fix(terminal): prevent escaping pane through scroll region (#3491)

zellij-server/src/panes/grid.rs

@@ -2745,7 +2745,9 @@ impl Perform for Grid {
                     .next()
                     .map(|param| param[0] as usize)
                     .filter(|&param| param != 0)
-                    .map(|bottom| bottom.saturating_sub(1));
+                    .map(|bottom| {
+                        std::cmp::min(self.height.saturating_sub(1), bottom.saturating_sub(1))
+                    });
                 self.set_scroll_region(top, bottom);
                 if self.erasure_mode {
                     self.move_cursor_to_line(top, EMPTY_TERMINAL_CHARACTER);

zellij-server/src/panes/unit/grid_tests.rs

@@ -3862,3 +3862,41 @@ fn text_ui_component_with_coordinates() {
     }
     assert_snapshot!(format!("{:?}", grid));
 }
+
+#[test]
+fn cannot_escape_scroll_region() {
+    // this tests a fix for a bug where it would be possible to set the scroll region bounds beyond
+    // the pane height, which would then allow a goto instruction beyond the scroll region to scape
+    // the pane bounds and render content on other panes
+    //
+    // what we do here is set the scroll region beyond the terminal bounds (`<ESC>[1;42r` - whereas
+    // the terminal is just 41 lines high), and then issue a goto instruction to line 42, one line
+    // beyond the pane and scroll region bounds (`<ESC>[42;1H`) and then print text `Hi there!`.
+    // This should be printed on the last line (zero indexed 40) of the terminal and not beyond it.
+    let mut vte_parser = vte::Parser::new();
+    let sixel_image_store = Rc::new(RefCell::new(SixelImageStore::default()));
+    let terminal_emulator_color_codes = Rc::new(RefCell::new(HashMap::new()));
+    let debug = false;
+    let arrow_fonts = true;
+    let styled_underlines = true;
+    let explicitly_disable_kitty_keyboard_protocol = false;
+    let mut grid = Grid::new(
+        41,
+        120,
+        Rc::new(RefCell::new(Palette::default())),
+        terminal_emulator_color_codes,
+        Rc::new(RefCell::new(LinkHandler::new())),
+        Rc::new(RefCell::new(None)),
+        sixel_image_store,
+        Style::default(),
+        debug,
+        arrow_fonts,
+        styled_underlines,
+        explicitly_disable_kitty_keyboard_protocol,
+    );
+    let content = "\u{1b}[1;42r\u{1b}[42;1HHi there!".as_bytes();
+    for byte in content {
+        vte_parser.advance(&mut grid, *byte);
+    }
+    assert_snapshot!(format!("{:?}", grid));
+}

zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__cannot_escape_scroll_region.snap

@@ -0,0 +1,47 @@
+---
+source: zellij-server/src/panes/./unit/grid_tests.rs
+assertion_line: 3894
+expression: "format!(\"{:?}\", grid)"
+---
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+36 (C):                                                                                                                         
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+38 (C):                                                                                                                         
+39 (C):                                                                                                                         
+40 (C): Hi there!                                                                                                               
+