Linux-Fsdevel Archive on lore.kernel.org
 help / color / Atom feed
From: Matthew Bobrowski <repnop@google.com>
To: jack@suse.cz, amir73il@gmail.com, christian.brauner@ubuntu.com
Cc: linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH 0/2] fanotify: Adding pidfd support to the fanotify API
Date: Fri, 16 Apr 2021 09:21:53 +1000
Message-ID: <cover.1618527437.git.repnop@google.com> (raw)

Hey Jan/Amir/Christian,

This is the RFC patch series for adding pidfd support to the fanotify
API.

tl;dr rather than returning a pid within struct
fanotify_event_metadata, a pidfd is returned instead when fanotify has
been explicitly told to do so via the new FAN_REPORT_PIDFD flag.

The main driver behind returning a pidfd within an event instead of a
pid is that it permits userspace applications to better detect if
they've possibly lost a TOCTOU race. A common paradigm among userspace
applications that make use of the fanotify API is to crawl /proc/<pid>
upon receiving an event. Userspace applications do this in order to
further ascertain contextual meta-information about the process that
was responsible for generating the filesystem event. On high pressure
systems, where pid recycling isn't uncommon, it's no longer considered
as a reliable approach to directly sift through /proc/<pid> and have
userspace applications use the information contained within
/proc/<pid> as it could, and does, lead to program execution
inaccuracies.

Now when a pidfd is returned in an event, a userspace application can:

    a) Obtain the pid responsible for generating the filesystem event
       from the pidfds fdinfo.

    b) Detect whether the userspace application lost the procfs access
       race by sending a 0 signal on the pidfd and checking the return
       value. A -ESRCH is indicative of the userspace application
       losing the race, meaning that the pid has been recycled.

Matthew Bobrowski (2):
  pidfd_create(): remove static qualifier and declare pidfd_create() in
    linux/pid.h
  fanotify: Add pidfd support to the fanotify API

 fs/notify/fanotify/fanotify_user.c | 33 +++++++++++++++++++++++++++---
 include/linux/fanotify.h           |  2 +-
 include/linux/pid.h                |  1 +
 include/uapi/linux/fanotify.h      |  2 ++
 kernel/pid.c                       |  2 +-
 5 files changed, 35 insertions(+), 5 deletions(-)

-- 
2.31.1.368.gbe11c130af-goog

/M

             reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15 23:21 Matthew Bobrowski [this message]
2021-04-15 23:22 ` [PATCH 1/2] pidfd_create(): remove static qualifier and declare pidfd_create() in linux/pid.h Matthew Bobrowski
2021-04-19 10:13   ` Jan Kara
2021-04-19 12:50   ` Christian Brauner
2021-04-20  0:17     ` Matthew Bobrowski
2021-04-15 23:22 ` [PATCH 2/2] fanotify: Add pidfd support to the fanotify API Matthew Bobrowski
2021-04-16  6:27   ` Amir Goldstein
2021-04-16  7:05     ` Matthew Bobrowski
2021-04-16  7:53       ` Amir Goldstein
2021-04-16  8:08         ` Matthew Bobrowski
2021-04-19 13:02     ` Christian Brauner
2021-04-19 10:21   ` Jan Kara
2021-04-20  1:35     ` Matthew Bobrowski
2021-04-19 13:20   ` Christian Brauner
2021-04-19 13:53     ` Amir Goldstein
2021-04-19 14:44       ` Christian Brauner
2021-04-19 13:55     ` Jan Kara
2021-04-19 15:02       ` Christian Brauner
2021-04-20  2:36         ` Matthew Bobrowski
2021-04-21  8:04           ` Jan Kara
2021-04-21  9:29             ` Amir Goldstein
2021-04-21 10:00               ` Jan Kara
2021-04-21 10:12                 ` Amir Goldstein
2021-04-21 13:48                   ` Jan Kara
2021-04-21 14:46                     ` Christian Brauner
2021-04-22 23:06             ` Matthew Bobrowski
2021-04-23  7:39               ` Amir Goldstein
2021-04-23  8:02                 ` Matthew Bobrowski
2021-04-23  8:14                   ` Amir Goldstein
2021-04-26 10:26                     ` Matthew Bobrowski
2021-04-26 11:11                       ` Amir Goldstein
2021-04-27  3:35                         ` Matthew Bobrowski
2021-04-27  5:14                           ` Amir Goldstein
2021-04-28 22:53                             ` Matthew Bobrowski
2021-04-19 12:34 ` [PATCH 0/2] fanotify: Adding " Christian Brauner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=cover.1618527437.git.repnop@google.com \
    --to=repnop@google.com \
    --cc=amir73il@gmail.com \
    --cc=christian.brauner@ubuntu.com \
    --cc=jack@suse.cz \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Fsdevel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \
		linux-fsdevel@vger.kernel.org
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-fsdevel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git