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.
---
 src/regexp_nfa.c                 | 3 ++-
 src/testdir/test_regexp_utf8.vim | 8 ++++++++
 src/version.c                    | 1 +
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index 064d90a..46604bd 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -5479,7 +5479,8 @@ 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 a7d1020..58386ac 100644
--- a/src/testdir/test_regexp_utf8.vim
+++ b/src/testdir/test_regexp_utf8.vim
@@ -558,4 +558,12 @@ func Test_match_char_class_upper()
   bwipe!
 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 c3c64d5..b34d74a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -5633,6 +5633,7 @@ static char *(extra_patches[]) =
 {   /* Add your patch description below this line */
     "8.2.3402",
     "8.2.3403",
+    "8.2.3409",
 /**/
     NULL
 };