From: Bram Moolenaar <Bram@vim.org>
Date: Tue, 7 Sep 2021 19:26:53 +0200
Subject: patch 8.2.3409: reading beyond end of line with invalid utf-8
 character

Problem:    Reading beyond end of line with invalid utf-8 character.
Solution:   Check for NUL when advancing.
(cherry picked from commit 65b605665997fad54ef39a93199e305af2fe4d7f)
---
 src/regexp_nfa.c                 |  3 ++-
 src/testdir/test_regexp_utf8.vim | 10 ++++++++++
 src/version.c                    |  1 +
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index 031a6cf..b9562c6 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -5414,7 +5414,8 @@ find_match_text(colnr_T startcol, int regstart, char_u *match_text)
 		match = FALSE;
 		break;
 	    }
-	    len2 += MB_CHAR2LEN(c2);
+	    len2 += enc_utf8 ? utf_ptr2len(rex.line + col + len2)
+							     : MB_CHAR2LEN(c2);
 	}
 	if (match
 		/* check that no composing char follows */
diff --git a/src/testdir/test_regexp_utf8.vim b/src/testdir/test_regexp_utf8.vim
index 98b9e73..75485dc 100644
--- a/src/testdir/test_regexp_utf8.vim
+++ b/src/testdir/test_regexp_utf8.vim
@@ -206,3 +206,13 @@ func Test_large_class()
   call assert_equal(1, "\u3042" =~# '[\u3000-\u4000]')
   set re=0
 endfunc
+
+func Test_match_invalid_byte()
+  call writefile(0z630a.765d30aa0a.2e0a.790a.4030, 'Xinvalid')
+  new
+  source Xinvalid
+  bwipe!
+  call delete('Xinvalid')
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index cfe1486..a3eca1e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -2582,6 +2582,7 @@ static char *(extra_patches[]) =
 {   /* Add your patch description below this line */
     "8.2.3402",
     "8.2.3403",
+    "8.2.3409",
 /**/
     NULL
 };