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Mon, 04 Mar 2024 09:42:01 -0800 (PST) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id u2-20020a17090341c200b001dd0d0d26a4sm2963663ple.147.2024.03.04.09.42.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Mar 2024 09:42:00 -0800 (PST) Date: Mon, 4 Mar 2024 09:42:00 -0800 From: Kees Cook To: Adrian Ratiu Cc: linux-fsdevel@vger.kernel.org, kernel@collabora.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, linux-doc@vger.kernel.org, Guenter Roeck , Doug Anderson , Jann Horn , Andrew Morton , Randy Dunlap , Christian Brauner , Mike Frysinger Subject: Re: [PATCH v2] proc: allow restricting /proc/pid/mem writes Message-ID: <202403040940.BAFD26EA4@keescook> References: <20240301213442.198443-1-adrian.ratiu@collabora.com> <202403011451.C236A38@keescook> <39f23-65e5d580-3-638b0780@155677577> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <39f23-65e5d580-3-638b0780@155677577> On Mon, Mar 04, 2024 at 02:06:43PM +0000, Adrian Ratiu wrote: > On Saturday, March 02, 2024 01:55 EET, Kees Cook wrote: > > On Fri, Mar 01, 2024 at 11:34:42PM +0200, Adrian Ratiu wrote: > > > [...] > > > +# define PROC_PID_MEM_MODE S_IRUSR > > > +#else > > > +# define PROC_PID_MEM_MODE (S_IRUSR|S_IWUSR) > > > +#endif > > > > PROC_PID_MEM_MODE will need to be a __ro_after_init variable, set by > > early_restrict_proc_mem_write, otherwise the mode won't change based on > > the runtime setting. e.g.: > > > > #ifdef CONFIG_SECURITY_PROC_MEM_RESTRICT_WRITE_DEFAULT_ON > > mode_t proc_pid_mem_mode __ro_after_init = S_IRUSR; > > #else > > mode_t proc_pid_mem_mode __ro_after_init = (S_IRUSR|S_IWUSR); > > #endif > > > > DEFINE_STATIC_KEY_MAYBE_RO(CONFIG_SECURITY_PROC_MEM_RESTRICT_WRITE_DEFAULT_ON, > > restrict_proc_mem_write); > > ... > > if (bool_result) { > > static_branch_enable(&restrict_proc_mem_write); > > proc_pid_mem_mode = S_IRUSR; > > } else { > > static_branch_disable(&restrict_proc_mem_write); > > proc_pid_mem_mode = (S_IRUSR|S_IWUSR); > > } > > ... > > REG("mem", proc_pid_mem_mode, proc_mem_operations), > > I'm having trouble implementing this because the proc_pid_mem_mode initializer needs to be a compile-time constant, so I can't set a runtime value in the REG() definition like suggested above. Ah. Yeah, so I guess just drop the perms change -- you're already checking the behavior in the open(), so you can just leave the perms alone. -- Kees Cook