From 8bd38863e61800ece97d88e4d1543d007a5055a6 Mon Sep 17 00:00:00 2001
From: Jan Edmund Lazo <jan.lazo@mail.utoronto.ca>
Date: Sun, 4 Oct 2020 18:33:21 -0400
Subject: [PATCH] vim-patch:8.1.1812: reading a truncted undo file hangs Vim

Problem:    Reading a truncted undo file hangs Vim.
Solution:   Check for reading EOF. (closes vim/vim#4769)
https://github.com/vim/vim/commit/fb06d767a8d76eead5391302fc88115d6e3879d8
---
 src/nvim/testdir/test_undo.vim | 19 +++++++++++++++++++
 src/nvim/undo.c                |  7 ++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/nvim/testdir/test_undo.vim b/src/nvim/testdir/test_undo.vim
index adcdcb1cd9..4a5825a08f 100644
--- a/src/nvim/testdir/test_undo.vim
+++ b/src/nvim/testdir/test_undo.vim
@@ -364,6 +364,25 @@ func Test_wundo_errors()
   bwipe!
 endfunc
 
+" Check that reading a truncted undo file doesn't hang.
+func Test_undofile_truncated()
+  throw 'skipped: TODO: '
+  new
+  call setline(1, 'hello')
+  set ul=100
+  wundo Xundofile
+  let contents = readfile('Xundofile', 'B')
+
+  " try several sizes
+  for size in range(20, 500, 33)
+    call writefile(contents[0:size], 'Xundofile')
+    call assert_fails('rundo Xundofile', 'E825:')
+  endfor
+
+  bwipe!
+"  call delete('Xundofile')
+endfunc
+
 func Test_rundo_errors()
   call assert_fails('rundo XfileDoesNotExist', 'E822:')
 
diff --git a/src/nvim/undo.c b/src/nvim/undo.c
index 903e57732f..6c5a6cdb46 100644
--- a/src/nvim/undo.c
+++ b/src/nvim/undo.c
@@ -878,7 +878,12 @@ static u_header_T *unserialize_uhp(bufinfo_T *bi,
   for (;; ) {
     int len = undo_read_byte(bi);
 
-    if (len == 0 || len == EOF) {
+    if (len == EOF) {
+      corruption_error("truncated", file_name);
+      u_free_uhp(uhp);
+      return NULL;
+    }
+    if (len == 0) {
       break;
     }
     int what = undo_read_byte(bi);