From: Christian Brauner <brauner@kernel.org>
Date: Wed, 22 Jul 2026 11:50:53 +0000 (+0200)
Subject: pidfs: preserve thread pidfds reopened by file handle
X-Git-Tag: v7.2-rc5~1^2~12^2~1
X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=bb6bc13c53e211d9148ed2eab3e689c5cd5c75da;p=thirdparty%2Flinux.git

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 <me@linux.beauty>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260716052726.1032092-1-me@linux.beauty
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---

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 = {