From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E739BC433ED for ; Mon, 19 Apr 2021 13:25:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B37DE61279 for ; Mon, 19 Apr 2021 13:25:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241171AbhDSN0U (ORCPT ); Mon, 19 Apr 2021 09:26:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:34014 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242068AbhDSNZQ (ORCPT ); Mon, 19 Apr 2021 09:25:16 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2843A61363; Mon, 19 Apr 2021 13:20:23 +0000 (UTC) Date: Mon, 19 Apr 2021 15:20:20 +0200 From: Christian Brauner To: Matthew Bobrowski Cc: jack@suse.cz, amir73il@gmail.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 2/2] fanotify: Add pidfd support to the fanotify API Message-ID: <20210419132020.ydyb2ly6e3clhe2j@wittgenstein> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Fri, Apr 16, 2021 at 09:22:25AM +1000, Matthew Bobrowski wrote: > Introduce a new flag FAN_REPORT_PIDFD for fanotify_init(2) which > allows userspace applications to control whether a pidfd is to be > returned instead of a pid for `struct fanotify_event_metadata.pid`. > > FAN_REPORT_PIDFD is mutually exclusive with FAN_REPORT_TID as the > pidfd API is currently restricted to only support pidfd generation for > thread-group leaders. Attempting to set them both when calling > fanotify_init(2) will result in -EINVAL being returned to the > caller. As the pidfd API evolves and support is added for tids, this > is something that could be relaxed in the future. > > If pidfd creation fails, the pid in struct fanotify_event_metadata is > set to FAN_NOPIDFD(-1). Falling back and providing a pid instead of a > pidfd on pidfd creation failures was considered, although this could > possibly lead to confusion and unpredictability within userspace > applications as distinguishing between whether an actual pidfd or pid > was returned could be difficult, so it's best to be explicit. > > Signed-off-by: Matthew Bobrowski > --- > fs/notify/fanotify/fanotify_user.c | 33 +++++++++++++++++++++++++++--- > include/linux/fanotify.h | 2 +- > include/uapi/linux/fanotify.h | 2 ++ > 3 files changed, 33 insertions(+), 4 deletions(-) > > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c > index 9e0c1afac8bd..fd8ae88796a8 100644 > --- a/fs/notify/fanotify/fanotify_user.c > +++ b/fs/notify/fanotify/fanotify_user.c > @@ -329,7 +329,7 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, > struct fanotify_info *info = fanotify_event_info(event); > unsigned int fid_mode = FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS); > struct file *f = NULL; > - int ret, fd = FAN_NOFD; > + int ret, pidfd, fd = FAN_NOFD; > int info_type = 0; > > pr_debug("%s: group=%p event=%p\n", __func__, group, event); > @@ -340,7 +340,25 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, > metadata.vers = FANOTIFY_METADATA_VERSION; > metadata.reserved = 0; > metadata.mask = event->mask & FANOTIFY_OUTGOING_EVENTS; > - metadata.pid = pid_vnr(event->pid); > + > + if (FAN_GROUP_FLAG(group, FAN_REPORT_PIDFD) && > + pid_has_task(event->pid, PIDTYPE_TGID)) { > + /* > + * Given FAN_REPORT_PIDFD is to be mutually exclusive with > + * FAN_REPORT_TID, panic here if the mutual exclusion is ever > + * blindly lifted without pidfds for threads actually being > + * supported. > + */ > + WARN_ON(FAN_GROUP_FLAG(group, FAN_REPORT_TID)); > + > + pidfd = pidfd_create(event->pid, 0); > + if (unlikely(pidfd < 0)) > + metadata.pid = FAN_NOPIDFD; > + else > + metadata.pid = pidfd; I'm not a fan of overloading fields (Yes, we did this for the _legacy_ clone() syscall for CLONE_PIDFD/CLONE_PARENT_SETTID but in general it's never a good idea if there are other options, imho.). Could/should we consider the possibility of adding a new pidfd field to struct fanotify_event_metadata? Christian