From cb0b99f0672d8446585d26e998343dceca17d1ce Mon Sep 17 00:00:00 2001
From: Christian Brabandt <cb@256bit.org>
Date: Tue, 14 Nov 2023 20:05:59 +0100
Subject: [PATCH] patch 9.0.2107: [security]: FPE in adjust_plines_for_skipcol

Problem:  [security]: FPE in adjust_plines_for_skipcol
Solution: don't divide by zero, return zero

Prevent a floating point exception when calculating w_skipcol (which can
happen with a small window when the number option is set and cpo+=n).

Add a test to verify

Signed-off-by: Christian Brabandt <cb@256bit.org>
---
 src/move.c                      |  5 +++--
 src/testdir/test_scroll_opt.vim | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/move.c b/src/move.c
index ce06dc3394689..fbb352a32e15a 100644
--- a/src/move.c
+++ b/src/move.c
@@ -45,8 +45,9 @@ adjust_plines_for_skipcol(win_T *wp)
 	return 0;
 
     int width = wp->w_width - win_col_off(wp);
-    if (wp->w_skipcol >= width)
-	return (wp->w_skipcol - width) / (width + win_col_off2(wp)) + 1;
+    int w2 = width + win_col_off2(wp);
+    if (wp->w_skipcol >= width && w2 > 0)
+	return (wp->w_skipcol - width) / w2 + 1;
 
     return 0;
 }
diff --git a/src/testdir/test_scroll_opt.vim b/src/testdir/test_scroll_opt.vim
index d5d08a24c20d4..342d382c20a5a 100644
--- a/src/testdir/test_scroll_opt.vim
+++ b/src/testdir/test_scroll_opt.vim
@@ -926,4 +926,23 @@ func Test_smoothscroll_cursor_top()
   call StopVimInTerminal(buf)
 endfunc
 
+" Division by zero, shouldn't crash
+func Test_smoothscroll_crash()
+  CheckScreendump
+
+  let lines =<< trim END
+      20 new
+      vsp
+      put =repeat('aaaa', 20)
+      set nu fdc=1  smoothscroll cpo+=n
+      vert resize 0
+      exe "norm! 0\<c-e>"
+  END
+  call writefile(lines, 'XSmoothScrollCrash', 'D')
+  let buf = RunVimInTerminal('-u NONE -S XSmoothScrollCrash', #{rows: 12, cols:40})
+  call term_sendkeys(buf, "2\<C-E>\<C-L>")
+
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
