From bb6bc13c53e211d9148ed2eab3e689c5cd5c75da Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 22 Jul 2026 13:50:53 +0200 Subject: [PATCH] pidfs: preserve thread pidfds reopened by file handle 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(). Signed-off-by: Li Chen Reviewed-by: Jan Kara Link: https://patch.msgid.link/20260716052726.1032092-1-me@linux.beauty Signed-off-by: Christian Brauner (Amutable) --- fs/pidfs.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/fs/pidfs.c b/fs/pidfs.c index aaa609ddab04..c20ffd747ff5 100644 --- a/fs/pidfs.c +++ b/fs/pidfs.c @@ -939,12 +939,18 @@ static int pidfs_export_permission(struct handle_to_path_ctx *ctx, static struct file *pidfs_export_open(const struct path *path, unsigned int oflags) { + struct file *file; + /* * Clear O_LARGEFILE as open_by_handle_at() forces it and raise * O_RDWR as pidfds always are. */ oflags &= ~O_LARGEFILE; - return dentry_open(path, oflags | O_RDWR, current_cred()); + file = dentry_open(path, oflags | O_RDWR, current_cred()); + /* do_dentry_open() strips O_EXCL, which encodes PIDFD_THREAD. */ + if (!IS_ERR(file)) + file->f_flags |= oflags & PIDFD_THREAD; + return file; } static const struct export_operations pidfs_export_operations = {