patch 8.2.3902: Vim9: double free with nested :def function

Problem:    Vim9: double free with nested :def function.
Solution:   Pass "line_to_free" from compile_def_function() and make sure
            cmdlinep is valid.

src/proto/userfunc.pro

@@ -38,7 +38,7 @@ char_u *untrans_function_name(char_u *name);
 char_u *get_scriptlocal_funcname(char_u *funcname);
 char_u *save_function_name(char_u **name, int *is_global, int skip, int flags, funcdict_T *fudi);
 void list_functions(regmatch_T *regmatch);
-ufunc_T *define_function(exarg_T *eap, char_u *name_arg);
+ufunc_T *define_function(exarg_T *eap, char_u *name_arg, char_u **line_to_free);
 void ex_function(exarg_T *eap);
 void ex_defcompile(exarg_T *eap);
 int eval_fname_script(char_u *p);

src/testdir/test_vim9_func.vim

@@ -1669,6 +1669,26 @@ def Test_error_in_nested_function()
   assert_fails('FuncWithForwardCall()', 'E1096:', '', 1, 'FuncWithForwardCall')
 enddef
 
+def Test_nested_functin_with_nextcmd()
+  var lines =<< trim END
+      vim9script
+      # Define an outer function
+      def FirstFunction()
+        # Define an inner function
+        def SecondFunction()
+          # the function has a body, a double free is detected.
+          AAAAA
+
+         # enddef followed by | or } followed by # one or more characters
+         enddef|BBBB
+      enddef
+
+      # Compile all functions
+      defcompile
+  END
+  CheckScriptFailure(lines, 'E476: Invalid command: AAAAA')
+enddef
+
 def Test_return_type_wrong()
   CheckScriptFailure([
         'def Func(): number',

src/userfunc.c

@@ -720,12 +720,14 @@ get_function_body(
 	}
 	else
 	{
-	    vim_free(*line_to_free);
 	    if (eap->getline == NULL)
 		theline = getcmdline(':', 0L, indent, getline_options);
 	    else
 		theline = eap->getline(':', eap->cookie, indent,
 							      getline_options);
+	    if (*eap->cmdlinep == *line_to_free)
+		*eap->cmdlinep = theline;
+	    vim_free(*line_to_free);
 	    *line_to_free = theline;
 	}
 	if (KeyTyped)
@@ -837,7 +839,8 @@ get_function_body(
 			// we can simply point into it, otherwise we need to
 			// change "eap->cmdlinep".
 			eap->nextcmd = nextcmd;
-			if (*line_to_free != NULL)
+			if (*line_to_free != NULL
+					    && *eap->cmdlinep != *line_to_free)
 			{
 			    vim_free(*eap->cmdlinep);
 			    *eap->cmdlinep = *line_to_free;
@@ -1161,7 +1164,7 @@ lambda_function_body(
 	}
 	if (ga_grow(gap, 1) == FAIL || ga_grow(freegap, 1) == FAIL)
 	    goto erret;
-	if (cmdline != NULL)
+	if (eap.nextcmd != NULL)
 	    // more is following after the "}", which was skipped
 	    last = cmdline;
 	else
@@ -1175,7 +1178,7 @@ lambda_function_body(
 	((char_u **)freegap->ga_data)[freegap->ga_len++] = pnl;
     }
 
-    if (cmdline != NULL)
+    if (eap.nextcmd != NULL)
     {
 	garray_T *tfgap = &evalarg->eval_tofree_ga;
 
@@ -1187,6 +1190,8 @@ lambda_function_body(
 	{
 	    ((char_u **)(tfgap->ga_data))[tfgap->ga_len++] = cmdline;
 	    evalarg->eval_using_cmdline = TRUE;
+	    if (cmdline == line_to_free)
+		line_to_free = NULL;
 	}
     }
     else
@@ -3988,9 +3993,8 @@ list_functions(regmatch_T *regmatch)
  * Returns a pointer to the function or NULL if no function defined.
  */
     ufunc_T *
-define_function(exarg_T *eap, char_u *name_arg)
+define_function(exarg_T *eap, char_u *name_arg, char_u **line_to_free)
 {
-    char_u	*line_to_free = NULL;
     int		j;
     int		c;
     int		saved_did_emsg;
@@ -4258,7 +4262,7 @@ define_function(exarg_T *eap, char_u *name_arg)
     if (get_function_args(&p, ')', &newargs,
 			eap->cmdidx == CMD_def ? &argtypes : NULL, FALSE,
 			 NULL, &varargs, &default_args, eap->skip,
-			 eap, &line_to_free) == FAIL)
+			 eap, line_to_free) == FAIL)
 	goto errret_2;
     whitep = p;
 
@@ -4368,7 +4372,7 @@ define_function(exarg_T *eap, char_u *name_arg)
 
     // Do not define the function when getting the body fails and when
     // skipping.
-    if (get_function_body(eap, &newlines, line_arg, &line_to_free) == FAIL
+    if (get_function_body(eap, &newlines, line_arg, line_to_free) == FAIL
 	    || eap->skip)
 	goto erret;
 
@@ -4660,7 +4664,6 @@ errret_2:
     }
 ret_free:
     ga_clear_strings(&argtypes);
-    vim_free(line_to_free);
     vim_free(fudi.fd_newkey);
     if (name != name_arg)
 	vim_free(name);
@@ -4676,7 +4679,10 @@ ret_free:
     void
 ex_function(exarg_T *eap)
 {
-    (void)define_function(eap, NULL);
+    char_u *line_to_free = NULL;
+
+    (void)define_function(eap, NULL, &line_to_free);
+    vim_free(line_to_free);
 }
 
 /*

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3902,
 /**/
     3901,
 /**/

src/vim9compile.c

@@ -812,11 +812,13 @@ func_needs_compiling(ufunc_T *ufunc, compiletype_T compile_type)
  * Compile a nested :def command.
  */
     static char_u *
-compile_nested_function(exarg_T *eap, cctx_T *cctx)
+compile_nested_function(exarg_T *eap, cctx_T *cctx, char_u **line_to_free)
 {
     int		is_global = *eap->arg == 'g' && eap->arg[1] == ':';
     char_u	*name_start = eap->arg;
     char_u	*name_end = to_name_end(eap->arg, TRUE);
+    int		off;
+    char_u	*func_name;
     char_u	*lambda_name;
     ufunc_T	*ufunc;
     int		r = FAIL;
@@ -866,7 +868,17 @@ compile_nested_function(exarg_T *eap, cctx_T *cctx)
     lambda_name = vim_strsave(get_lambda_name());
     if (lambda_name == NULL)
 	return NULL;
-    ufunc = define_function(eap, lambda_name);
+
+    // This may free the current line, make a copy of the name.
+    off = is_global ? 2 : 0;
+    func_name = vim_strnsave(name_start + off, name_end - name_start - off);
+    if (func_name == NULL)
+    {
+	r = FAIL;
+	goto theend;
+    }
+
+    ufunc = define_function(eap, lambda_name, line_to_free);
 
     if (ufunc == NULL)
     {
@@ -911,21 +923,14 @@ compile_nested_function(exarg_T *eap, cctx_T *cctx)
 
     if (is_global)
     {
-	char_u *func_name = vim_strnsave(name_start + 2,
+	r = generate_NEWFUNC(cctx, lambda_name, func_name);
-						    name_end - name_start - 2);
+	func_name = NULL;
-
+	lambda_name = NULL;
-	if (func_name == NULL)
-	    r = FAIL;
-	else
-	{
-	    r = generate_NEWFUNC(cctx, lambda_name, func_name);
-	    lambda_name = NULL;
-	}
     }
     else
     {
 	// Define a local variable for the function reference.
-	lvar_T	*lvar = reserve_local(cctx, name_start, name_end - name_start,
+	lvar_T	*lvar = reserve_local(cctx, func_name, name_end - name_start,
 						    TRUE, ufunc->uf_func_type);
 
 	if (lvar == NULL)
@@ -937,6 +942,7 @@ compile_nested_function(exarg_T *eap, cctx_T *cctx)
 
 theend:
     vim_free(lambda_name);
+    vim_free(func_name);
     return r == FAIL ? NULL : (char_u *)"";
 }
 
@@ -2861,7 +2867,7 @@ compile_def_function(
 	    case CMD_def:
 	    case CMD_function:
 		    ea.arg = p;
-		    line = compile_nested_function(&ea, &cctx);
+		    line = compile_nested_function(&ea, &cctx, &line_to_free);
 		    break;
 
 	    case CMD_return:

src/vim9execute.c

@@ -3345,10 +3345,12 @@ exec_instructions(ectx_T *ectx)
 		else
 		{
 		    exarg_T ea;
+		    char_u  *line_to_free = NULL;
 
 		    CLEAR_FIELD(ea);
 		    ea.cmd = ea.arg = iptr->isn_arg.string;
-		    define_function(&ea, NULL);
+		    define_function(&ea, NULL, &line_to_free);
+		    vim_free(line_to_free);
 		}
 		break;