api: fix use-after-free in nvim_chan_send

src/nvim/api/vim.c

@@ -1333,7 +1333,8 @@ void nvim_chan_send(Integer chan, String data, Error *err)
     return;
   }
 
-  channel_send((uint64_t)chan, data.data, data.size, &error);
+  channel_send((uint64_t)chan, data.data, data.size,
+               false, &error);
   if (error) {
     api_set_error(err, kErrorTypeValidation, "%s", error);
   }

src/nvim/channel.c

@@ -499,48 +499,54 @@ uint64_t channel_from_stdio(bool rpc, CallbackReader on_output,
 }
 
 /// @param data will be consumed
-size_t channel_send(uint64_t id, char *data, size_t len, const char **error)
+size_t channel_send(uint64_t id, char *data, size_t len,
+                    bool data_owned, const char **error)
 {
   Channel *chan = find_channel(id);
+  size_t written = 0;
   if (!chan) {
     *error = _(e_invchan);
-    goto err;
+    goto retfree;
   }
 
   if (chan->streamtype == kChannelStreamStderr) {
     if (chan->stream.err.closed) {
       *error = _("Can't send data to closed stream");
-      goto err;
+      goto retfree;
     }
     // unbuffered write
-    size_t written = fwrite(data, len, 1, stderr);
-    xfree(data);
-    return len * written;
+    written = len * fwrite(data, len, 1, stderr);
+    goto retfree;
   }
 
   if (chan->streamtype == kChannelStreamInternal && chan->term) {
     terminal_receive(chan->term, data, len);
-    return len;
+    written = len;
+    goto retfree;
   }
 
 
   Stream *in = channel_instream(chan);
   if (in->closed) {
     *error = _("Can't send data to closed stream");
-    goto err;
+    goto retfree;
   }
 
   if (chan->is_rpc) {
     *error = _("Can't send raw data to rpc channel");
-    goto err;
+    goto retfree;
   }
 
-  WBuffer *buf = wstream_new_buffer(data, len, 1, xfree);
+  // write can be delayed indefinitely, so always use an allocated buffer
+  WBuffer *buf = wstream_new_buffer(data_owned ? data : xmemdup(data, len),
+                                    len, 1, xfree);
   return wstream_write(in, buf) ? len : 0;
 
-err:
+retfree:
+  if (data_owned) {
     xfree(data);
-  return 0;
+  }
+  return written;
 }
 
 /// Convert binary byte array to a readfile()-style list

src/nvim/eval/funcs.c

@@ -916,7 +916,7 @@ static void f_chansend(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   }
   uint64_t id = argvars[0].vval.v_number;
   const char *error = NULL;
-  rettv->vval.v_number = channel_send(id, input, input_len, &error);
+  rettv->vval.v_number = channel_send(id, input, input_len, true, &error);
   if (error) {
     EMSG(error);
   }

test/functional/core/job_spec.lua

@@ -963,8 +963,10 @@ describe('jobs', function()
       return rv
     end
 
+    local j
     local function send(str)
-      nvim('command', 'call jobsend(j, "'..str..'")')
+      -- check no nvim_chan_free double free with pty job (#14198)
+      meths.chan_send(j, str)
     end
 
     before_each(function()
@@ -979,6 +981,7 @@ describe('jobs', function()
       nvim('command', 'let g:job_opts.pty = 1')
       nvim('command', 'let exec = [expand("<cfile>:p")]')
       nvim('command', "let j = jobstart(exec, g:job_opts)")
+      j = eval'j'
       eq('tty ready', next_chunk())
     end)