patch 9.2.0131: potential buffer overflow in regdump()

Problem:  Potential buffer overflow in regdump()
Solution: Add the size to the compiled regular expression and ensure we
          don't read over the limit.

Note: this is not a security issue, because regdump() is typically not
compiled in any version of Vim, so should not affect anybody.

supported by AI claude.

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/regexp.h

@@ -73,6 +73,9 @@ typedef struct
     char_u		reganch;
     char_u		*regmust;
     int			regmlen;
+#ifdef DEBUG
+    int			regsz;
+#endif
 #ifdef FEAT_SYN_HL
     char_u		reghasz;
 #endif

src/regexp_bt.c

@@ -2497,6 +2497,9 @@ bt_regcomp(char_u *expr, int re_flags)
     if (r == NULL)
 	return NULL;
     r->re_in_use = FALSE;
+#ifdef DEBUG
+    r->regsz = regsize;
+#endif
 
     // Second pass: emit code.
     regcomp_start(expr, re_flags);
@@ -5200,11 +5203,11 @@ regdump(char_u *pattern, bt_regprog_T *r)
     s = r->program + 1;
     // Loop until we find the END that isn't before a referred next (an END
     // can also appear in a NOMATCH operand).
-    while (op != END || s <= end)
+    while ((op != END || s <= end) && s < r->program + r->regsz)
     {
 	op = OP(s);
 	fprintf(f, "%2d%s", (int)(s - r->program), regprop(s)); // Where, what.
-	next = regnext(s);
+	next = (s + 3 <= r->program + r->regsz) ? regnext(s) : NULL;
 	if (next == NULL)	// Next ptr.
 	    fprintf(f, "(0)");
 	else
@@ -5230,14 +5233,22 @@ regdump(char_u *pattern, bt_regprog_T *r)
 	    s += 5;
 	}
 	s += 3;
+	if (op == MULTIBYTECODE)
+	{
+	    fprintf(f, " mbc=%d", utf_ptr2char(s));
+	    s += utfc_ptr2len(s);
+	}
 	if (op == ANYOF || op == ANYOF + ADD_NL
 		|| op == ANYBUT || op == ANYBUT + ADD_NL
 		|| op == EXACTLY)
 	{
 	    // Literal string, where present.
 	    fprintf(f, "\nxxxxxxxxx\n");
-	    while (*s != NUL)
-		fprintf(f, "%c", *s++);
+	    while (*s != NUL && s < r->program + r->regsz)
+	    {
+		fprintf(f, "%c", *s);
+		s += utfc_ptr2len(s);  // advance by full char including combining
+	    }
 	    fprintf(f, "\nxxxxxxxxx\n");
 	    s++;
 	}

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    131,
 /**/
     130,
 /**/