Merge pull request #17991 from zeertzjq/vim-8.2.4253

vim-patch:8.2.4253: using freed memory when substitute with function call

src/nvim/ex_cmds.c

@@ -3627,15 +3627,22 @@ static buf_T *do_sub(exarg_T *eap, proftime_T timeout, bool do_buf_event, handle
 
   sub_firstline = NULL;
 
-  // ~ in the substitute pattern is replaced with the old pattern.
-  // We do it here once to avoid it to be replaced over and over again.
-  // But don't do it when it starts with "\=", then it's an expression.
   assert(sub != NULL);
 
   bool sub_needs_free = false;
-  if (!(sub[0] == '\\' && sub[1] == '=')) {
+  char_u *sub_copy = NULL;
+
+  // If the substitute pattern starts with "\=" then it's an expression.
+  // Make a copy, a recursive function may free it.
+  // Otherwise, '~' in the substitute pattern is replaced with the old
+  // pattern.  We do it here once to avoid it to be replaced over and over
+  // again.
+  if (sub[0] == '\\' && sub[1] == '=') {
+    sub = vim_strsave(sub);
+    sub_copy = sub;
+  } else {
     char_u *source = sub;
-    sub = regtilde(sub, p_magic);
+    sub = regtilde(sub, p_magic, preview);
     // When previewing, the new pattern allocated by regtilde() needs to be freed
     // in this function because it will not be used or freed by regtilde() later.
     sub_needs_free = preview && sub != source;
@@ -4412,6 +4419,10 @@ skip:
   }
 
   vim_regfree(regmatch.regprog);
+  xfree(sub_copy);
+  if (sub_needs_free) {
+    xfree(sub);
+  }
 
   // Restore the flag values, they can be used for ":&&".
   subflags.do_all = save_do_all;
@@ -4444,10 +4455,6 @@ skip:
 
   kv_destroy(preview_lines.subresults);
 
-  if (sub_needs_free) {
-    xfree(sub);
-  }
-
   return preview_buf;
 #undef ADJUST_SUB_FIRSTLNUM
 #undef PUSH_PREVIEW_LINES

src/nvim/regexp.c

@@ -1531,7 +1531,7 @@ static fptr_T do_Lower(int *d, int c)
  *
  * The tildes are parsed once before the first call to vim_regsub().
  */
-char_u *regtilde(char_u *source, int magic)
+char_u *regtilde(char_u *source, int magic, bool preview)
 {
   char_u      *newsub = source;
   char_u      *tmpsub;
@@ -1576,7 +1576,7 @@ char_u *regtilde(char_u *source, int magic)
   }
 
   // Only change reg_prev_sub when not previewing.
-  if (!(State & CMDPREVIEW)) {
+  if (!preview) {
     xfree(reg_prev_sub);
     if (newsub != source) {             // newsub was allocated, just keep it
       reg_prev_sub = newsub;

src/nvim/shada.c

@@ -1238,7 +1238,7 @@ static void shada_read(ShaDaReadDef *const sd_reader, const int flags)
       // string is close to useless: you can only use it with :& or :~ and
       // that’s all because s//~ is not available until the first call to
       // regtilde. Vim was not calling this for some reason.
-      (void)(char *)regtilde((char_u *)cur_entry.data.sub_string.sub, p_magic);
+      (void)(char *)regtilde((char_u *)cur_entry.data.sub_string.sub, p_magic, false);
       // Do not free shada entry: its allocated memory was saved above.
       break;
     case kSDItemHistoryEntry:

src/nvim/testdir/test_substitute.vim

@@ -819,4 +819,22 @@ func Test_substitute_skipped_range()
   bwipe!
 endfunc
 
+" This was using "old_sub" after it was freed.
+func Test_using_old_sub()
+  " set compatible maxfuncdepth=10
+  set maxfuncdepth=10
+  new
+  call setline(1, 'some text.')
+  func Repl()
+    ~
+    s/
+  endfunc
+  silent!  s/\%')/\=Repl()
+
+  delfunc Repl
+  bwipe!
+  set nocompatible
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab