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From: Johannes Weiner <hannes@cmpxchg.org>
To: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>,
	tj@kernel.org, lizefan.x@bytedance.com, peterz@infradead.org,
	johunt@akamai.com, keescook@chromium.org,
	quic_sudaraja@quicinc.com, cgroups@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] psi: remove 500ms min window size limitation for triggers
Date: Thu, 2 Mar 2023 12:58:57 -0500	[thread overview]
Message-ID: <ZADj4YX4uftK/Frh@cmpxchg.org> (raw)
In-Reply-To: <ZADf27Kx5mbFev+I@dhcp22.suse.cz>

On Thu, Mar 02, 2023 at 06:41:47PM +0100, Michal Hocko wrote:
> On Thu 02-03-23 08:13:54, Suren Baghdasaryan wrote:
> [...]
> > Let's roll this check without additional changes and then consolidate
> > the checking inside psi_trigger_create() in a separate patch. If
> > anybody objects to the late permission check we will just revert that
> > last change without affecting anything else.
> 
> Permissions checks at write time are problematic because userspace
> cannot drop privileges. Also I think it would be an antipattern for how
> we do this in general. 

The permissions can be checked against opener privileges through
file->f_cred. This allows dropping privileges, as well as passing the
fd to a trusted but unprivileged process to delegate trigger setup.

I agree with keeping it in open() for now. But it will matter when we
distinguish between privileged and unprivileged trigger parameters.

WARNING: multiple messages have this Message-ID (diff)
From: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
To: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
Cc: Suren Baghdasaryan
	<surenb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
	lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org,
	peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org,
	johunt-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org,
	keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org,
	quic_sudaraja-jfJNa2p1gH1BDgjK7y7TUQ@public.gmane.org,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 1/1] psi: remove 500ms min window size limitation for triggers
Date: Thu, 2 Mar 2023 12:58:57 -0500	[thread overview]
Message-ID: <ZADj4YX4uftK/Frh@cmpxchg.org> (raw)
In-Reply-To: <ZADf27Kx5mbFev+I-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>

On Thu, Mar 02, 2023 at 06:41:47PM +0100, Michal Hocko wrote:
> On Thu 02-03-23 08:13:54, Suren Baghdasaryan wrote:
> [...]
> > Let's roll this check without additional changes and then consolidate
> > the checking inside psi_trigger_create() in a separate patch. If
> > anybody objects to the late permission check we will just revert that
> > last change without affecting anything else.
> 
> Permissions checks at write time are problematic because userspace
> cannot drop privileges. Also I think it would be an antipattern for how
> we do this in general. 

The permissions can be checked against opener privileges through
file->f_cred. This allows dropping privileges, as well as passing the
fd to a trusted but unprivileged process to delegate trigger setup.

I agree with keeping it in open() for now. But it will matter when we
distinguish between privileged and unprivileged trigger parameters.

  reply	other threads:[~2023-03-02 17:59 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-01 19:34 [PATCH 1/1] psi: remove 500ms min window size limitation for triggers Suren Baghdasaryan
2023-03-01 19:34 ` Suren Baghdasaryan
2023-03-01 20:07 ` Johannes Weiner
2023-03-01 20:07   ` Johannes Weiner
2023-03-01 20:48   ` Suren Baghdasaryan
2023-03-01 20:48     ` Suren Baghdasaryan
2023-03-01 21:00     ` Kalesh Singh
2023-03-01 21:00       ` Kalesh Singh
2023-03-02 15:30     ` Johannes Weiner
2023-03-02 15:30       ` Johannes Weiner
2023-03-02 16:13       ` Suren Baghdasaryan
2023-03-02 16:13         ` Suren Baghdasaryan
2023-03-02 17:41         ` Michal Hocko
2023-03-02 17:41           ` Michal Hocko
2023-03-02 17:58           ` Johannes Weiner [this message]
2023-03-02 17:58             ` Johannes Weiner
2023-03-02 13:58 ` Michal Hocko
2023-03-02 16:08   ` Suren Baghdasaryan
2023-03-02 16:08     ` Suren Baghdasaryan
2023-03-02 17:39     ` Michal Hocko
2023-03-02 17:39       ` Michal Hocko

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