Hi Jan & Christian, ---- On Mon, 27 Jul 2026 23:57:14 +0800 Jan Kara <[email protected]> wrote --- > On Wed 22-07-26 14:07:37, Christian Brauner wrote: > > On 2026-07-16 13:11 +0200, Jan Kara wrote: > > > On Thu 16-07-26 13:27:22, Li Chen wrote: > > > > PIDFD_THREAD shares O_EXCL. do_dentry_open() clears O_EXCL after > > > > pidfs_export_open() validates the flags, so open_by_handle_at() > > > > silently turns a thread pidfd into a process pidfd. > > > > > > > > Restore PIDFD_THREAD on the opened file, matching pidfs_alloc_file(), > > > > and cover the restored flag with F_GETFL. > > > > > > > > Signed-off-by: Li Chen <[email protected]> > > > > > > Makes sense. Just looking at this code, what about PIDFD_AUTOKILL (aka > > > O_TRUNC?)? Reading the commit introducing it 07c3ef58223e it appears it > > > was > > > never meant to be directly requested by userspace so probably > > > pidfs_export_open() needs to reject it. But that's unrelated issue to > > > your > > > patch so feel free to add: > > > > Good point. But pidfs_export_open() is guarded by > > pidfs_export_permission() which does: > > > > #define VALID_FILE_HANDLE_OPEN_FLAGS \ > > (O_RDONLY | O_WRONLY | O_RDWR | O_NONBLOCK | O_CLOEXEC | O_EXCL) > > > > if (oflags & ~(VALID_FILE_HANDLE_OPEN_FLAGS | O_LARGEFILE)) > > return -EINVAL; > > > > and so is safe. But I've added the following patch on top which also > > splats if that is passed! > > > > From 99a859485394eca8cf6271de09ae72ac3b846bda Mon Sep 17 00:00:00 2001 > > From: Christian Brauner <[email protected]> > > Date: Wed, 22 Jul 2026 13:56:28 +0200 > > Subject: [PATCH] pidfs: add pidfs_dentry_open() helper > > > > Both pidfs_alloc_file() and pidfs_export_open() need to force O_RDWR > > and reapply the pidfd flags that do_dentry_open() strips. Move the > > common logic into a helper. > > > > PIDFD_AUTOKILL is now part of the restore mask in the file handle path > > as well, but pidfs_export_permission() rejects O_TRUNC, so this is a > > no-op there. But warn nonetheless. > > > > Signed-off-by: Christian Brauner (Amutable) <[email protected]> > > Nice! Feel free to add: > > Reviewed-by: Jan Kara <[email protected]> >
> Both pidfs_alloc_file() and pidfs_export_open() need to force O_RDWR > and reapply the pidfd flags that do_dentry_open() strips. Move the > common logic into a helper. Thanks both. Jan, thanks for pointing out the PIDFD_AUTOKILL angle. Christian, thanks for factoring this into pidfs_dentry_open() and applying the fix. Regards, Li
