vim-patch:9.0.1969: [security] buffer-overflow in trunc_string()

Problem:  buffer-overflow in trunc_string()
Solution: Add NULL at end of buffer

Currently trunc_string() assumes that when the string is too long,
buf[e-1] will always be writeable. But that assumption may not always be
true. The condition currently looks like this

    else if (e + 3 < buflen)
    [...]
    else
    {
	// can't fit in the "...", just truncate it
	buf[e - 1] = NUL;
    }

but this means, we may run into the last else clause with e still being
larger than buflen. So a buffer overflow occurs.

So instead of using `buf[e - 1]`, let's just always
truncate at `buf[buflen - 1]` which should always be writable.

https://github.com/vim/vim/commit/3bd7fa12e146c6051490d048a4acbfba974eeb04

vim-patch:9.0.2004: Missing test file

Problem:  Missing test file
Solution: git-add the file to the repo

closes: vim/vim#13305

https://github.com/vim/vim/commit/d4afbdd0715c722cfc73d3a8ab9e578667615faa

Co-authored-by: Christian Brabandt <cb@256bit.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/test/functional/legacy/messages_spec.lua b/test/functional/legacy/messages_spec.lua
index a604e68822..7536506aa3 100644
--- a/test/functional/legacy/messages_spec.lua
+++ b/test/functional/legacy/messages_spec.lua
@@ -6,6 +6,7 @@ local exec = helpers.exec
 local feed = helpers.feed
 local meths = helpers.meths
 local nvim_dir = helpers.nvim_dir
+local assert_alive = helpers.assert_alive
 
 before_each(clear)
 
@@ -758,4 +759,9 @@ describe('messages', function()
     ]])
     os.remove('b.txt')
   end)
+
+  it('no crash when truncating overlong message', function()
+    pcall(command, 'source test/old/testdir/crash/vim_msg_trunc_poc')
+    assert_alive()
+  end)
 end)