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Thu, 02 Mar 2023 09:58:58 -0800 (PST) Date: Thu, 2 Mar 2023 12:58:57 -0500 From: Johannes Weiner To: Michal Hocko Cc: Suren Baghdasaryan , 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 Message-ID: References: <20230301193403.1507484-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E3269120017 X-Rspam-User: X-Stat-Signature: nz9cn1xtxh3awbtjyddahjj3nnceizju X-HE-Tag: 1677779939-756617 X-HE-Meta: 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 B9lV1dK/ EyaSAWwaw+XAWnPZr6zqO1A0FBytRMOjfjppjt1kjwDFfrhmGoqZkchrnK3MTcJmuH5pmudKdkKTYeBoUYR+h1QOqIA59mvXBcuN6gjXZ+hAWr/54jtM45TNnd1om3wFmv7X1PZ3cFwmPjZ+7+wEIOYIOXSoR9P84iFYXKkDiBY2hObAX8Dep/0BLDzfYdbhriyEGK9ZVIGEUFT19ykknbCf007twOu1YTDYnoeevYHInbS+QJU1Mcaa/GYqHJbqfkwLULE/bRawfRrzRnmDHeSM3i+sogl/FDsZHe37R2+XwVH3sJf3tB7uYmUOfqwMasAMo/j1JiAJ9FkOZr+KgKtF0dRYB8AV4Cfx7HtdwtEpXHzKlmOUtxKSjjSaZxfEH/LkOF4Lgvkzrf86GASTxh5vb8Yd0mHgzE6Oc X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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.