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From: Matthew Bobrowski <repnop@google.com>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Jan Kara <jack@suse.cz>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Linux API <linux-api@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 2/2] fanotify: Add pidfd support to the fanotify API
Date: Fri, 16 Apr 2021 18:08:16 +1000
Message-ID: <YHlF8El4lcsHNYtR@google.com> (raw)
In-Reply-To: <CAOQ4uxjQi4dV0XoU2WDKG+3R81Xam6giee9hhkvXb13tQB+Tdg@mail.gmail.com>

On Fri, Apr 16, 2021 at 10:53:48AM +0300, Amir Goldstein wrote:
> On Fri, Apr 16, 2021 at 10:06 AM Matthew Bobrowski <repnop@google.com> wrote:
> > > > +               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.
> >
> > ACK.
> >
> > > Need to make sure that pidfd is not reported to an unprivileged
> > > listener even if group was initialized by a privileged process.
> > > This is a conscious conservative choice that we made for reporting
> > > pid info to unprivileged listener that can be revisited in the future.
> >
> > OK, I see. In that case, I guess I can add the FAN_REPORT_PIDFD check
> > above the current conditional [0]:
> >
> > ...
> > if (!capable(CAP_SYS_ADMIN) && task_tgid(current) != event->pid)
> >         metadata.pid = 0;
> > ...
> >
> > That way, AFAIK even if it is an unprivileged listener the pid info
> > will be overwritten as intended.
> >
> 
> Situation is a bit more subtle than that.
> If you override event->pid with zero and zero is interpreted as pidfd
> that would not be consistent with uapi documentation.

Ah, yes, of course! I had totally overlooked this. Also, speaking of
UAPI documentation, I'll have it prepared along with the LTP tests
once I get the ACK for this particular concept from Jan and Christian.

> You need to make sure that event->pid is FAN_NOPIDFD in case
> (!capable(CAP_SYS_ADMIN) &&
>  FAN_GROUP_FLAG(group, FAN_REPORT_PIDFD))
> Hopefully, you can do that while keeping the special cases to minimum...

I don't foresee any issues with doing this at all.

/M

  reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15 23:21 [PATCH 0/2] fanotify: Adding " 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 [this message]
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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