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=-18.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 598EFC43461 for ; Mon, 19 Apr 2021 13:02:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 276F66113C for ; Mon, 19 Apr 2021 13:02:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237532AbhDSNCo (ORCPT ); Mon, 19 Apr 2021 09:02:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:40856 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238205AbhDSNCn (ORCPT ); Mon, 19 Apr 2021 09:02:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id ED1E061107; Mon, 19 Apr 2021 13:02:10 +0000 (UTC) Date: Mon, 19 Apr 2021 15:02:07 +0200 From: Christian Brauner To: Amir Goldstein Cc: Matthew Bobrowski , Jan Kara , Linux API , linux-fsdevel Subject: Re: [PATCH 2/2] fanotify: Add pidfd support to the fanotify API Message-ID: <20210419130207.j5zi3ulsgbbbypsm@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-fsdevel@vger.kernel.org On Fri, Apr 16, 2021 at 09:27:03AM +0300, Amir Goldstein wrote: > On Fri, Apr 16, 2021 at 2:22 AM 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). > > Hi Matthew, > > All in all looks good, just a few small nits. > > > 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. > > I don't think this should have been even "considered" so I see little > value in this paragraph in commit message. > > > > > 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)); > > Better WARN_ON_ONCE() the outcome of this error is not terrible. > Also in the comment above I would not refer to this warning as "panic". > > > + > > + pidfd = pidfd_create(event->pid, 0); > > + if (unlikely(pidfd < 0)) > > + metadata.pid = FAN_NOPIDFD; > > + else > > + metadata.pid = pidfd; > > + } else { > > + metadata.pid = pid_vnr(event->pid); > > + } > > You should rebase your work on: > git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git fsnotify > and resolve conflicts with "unprivileged listener" code. > > Need to make sure that pidfd is not reported to an unprivileged > listener even if group was initialized by a privileged process. I agree.