From: Markus Koschany <apo@debian.org>
Date: Sun, 11 Jun 2023 13:58:23 +0200
Subject: CVE-2023-2610

Bug-Debian: https://bugs.debian.org/1035955
Origin: https://github.com/vim/vim/commit/ab9a2d884b3a4abe319606ea95a5a6d6b01cd73a
---
 src/regexp.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/src/regexp.c b/src/regexp.c
index 6939fd1..5630364 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -7150,10 +7150,7 @@ do_Lower(int *d, int c)
 regtilde(char_u *source, int magic)
 {
     char_u	*newsub = source;
-    char_u	*tmpsub;
     char_u	*p;
-    int		len;
-    int		prevlen;
 
     for (p = newsub; *p; ++p)
     {
@@ -7162,24 +7159,34 @@ regtilde(char_u *source, int magic)
 	    if (reg_prev_sub != NULL)
 	    {
 		/* length = len(newsub) - 1 + len(prev_sub) + 1 */
-		prevlen = (int)STRLEN(reg_prev_sub);
-		tmpsub = alloc((unsigned)(STRLEN(newsub) + prevlen));
+		// Avoid making the text longer than MAXCOL, it will cause
+		// trouble at some point.
+		size_t	prevsublen = STRLEN(reg_prev_sub);
+		size_t  newsublen = STRLEN(newsub);
+		if (prevsublen > MAXCOL || newsublen > MAXCOL
+					    || newsublen + prevsublen > MAXCOL)
+		{
+		    break;
+		}
+
+		char_u *tmpsub = alloc(newsublen + prevsublen);
 		if (tmpsub != NULL)
 		{
 		    /* copy prefix */
-		    len = (int)(p - newsub);	/* not including ~ */
-		    mch_memmove(tmpsub, newsub, (size_t)len);
+		    size_t prefixlen = p - newsub;	// not including ~
+		    mch_memmove(tmpsub, newsub, prefixlen);
 		    /* interpret tilde */
-		    mch_memmove(tmpsub + len, reg_prev_sub, (size_t)prevlen);
+		    mch_memmove(tmpsub + prefixlen, reg_prev_sub,
+							       prevsublen);
 		    /* copy postfix */
 		    if (!magic)
 			++p;			/* back off \ */
-		    STRCPY(tmpsub + len + prevlen, p + 1);
+		    STRCPY(tmpsub + prefixlen + prevsublen, p + 1);
 
-		    if (newsub != source)	/* already allocated newsub */
+		    if (newsub != source)	// allocated newsub before
 			vim_free(newsub);
 		    newsub = tmpsub;
-		    p = newsub + len + prevlen;
+		    p = newsub + prefixlen + prevsublen;
 		}
 	    }
 	    else if (magic)