eventfs: Have event files and directories default to parent uid and gid

commit 0dfc852b upstream.

Dongliang reported:

  I found that in the latest version, the nodes of tracefs have been
  changed to dynamically created.

  This has caused me to encounter a problem where the gid I specified in
  the mounting parameters cannot apply to all files, as in the following
  situation:

  /data/tmp/events # mount | grep tracefs
  tracefs on /data/tmp type tracefs (rw,seclabel,relatime,gid=3012)

  gid 3012 = readtracefs

  /data/tmp # ls -lh
  total 0
  -r--r-----   1 root readtracefs 0 1970-01-01 08:00 README
  -r--r-----   1 root readtracefs 0 1970-01-01 08:00 available_events

  ums9621_1h10:/data/tmp/events # ls -lh
  total 0
  drwxr-xr-x 2 root root 0 2023-12-19 00:56 alarmtimer
  drwxr-xr-x 2 root root 0 2023-12-19 00:56 asoc

  It will prevent certain applications from accessing tracefs properly, I
  try to avoid this issue by making the following modifications.

To fix this, have the files created default to taking the ownership of
the parent dentry unless the ownership was previously set by the user.

Link: https://lore.kernel.org/linux-trace-kernel/1703063706-30539-1-git-send-email-dongliang.cui@unisoc.com/
Link: https://lore.kernel.org/linux-trace-kernel/20231220105017.1489d790@gandalf.local.home



Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Hongyu Jin  <hongyu.jin@unisoc.com>
Fixes: 28e12c09 ("eventfs: Save ownership and mode")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reported-by: Dongliang Cui <cuidongliang390@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>