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* [PATCH 0/2] fanotify: Adding pidfd support to the fanotify API
@ 2021-04-15 23:21 Matthew Bobrowski
  2021-04-15 23:22 ` [PATCH 1/2] pidfd_create(): remove static qualifier and declare pidfd_create() in linux/pid.h Matthew Bobrowski
                   ` (2 more replies)
  0 siblings, 3 replies; 35+ messages in thread
From: Matthew Bobrowski @ 2021-04-15 23:21 UTC (permalink / raw)
  To: jack, amir73il, christian.brauner; +Cc: linux-api, linux-fsdevel

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

^ permalink raw reply	[flat|nested] 35+ messages in thread

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Thread overview: 35+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-04-15 23:21 [PATCH 0/2] fanotify: Adding pidfd support to the fanotify API Matthew Bobrowski
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

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