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s=20210705; t=1746690775; bh=G6zo5KYbksyRNfmQ8KKx8XVCr5lsyu8SUY/gEaHPlbY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dYkY/0pDZ84gMwQ+AKLc8UiT0CUE7jFkwOw7o1hkSZSXUI83tyhohsbbCE0ltzKZj rrnwCub67+2UYC8oouzCVnO/OjmIuXZ2FueW5WglNFuPmrsG5kh0iDxgJ5QSa3n4pp nkFK+UqidCNWffnHOiOSwfgdG7h0oY5HXzAX4Ck1yxrmgJvRSB96Xs5jaDvxP13Sji 0tRKsOWJj2RdsDfDFEah1ETO7Ke2dq5Y5QmJ9FVh4SFZdn+biOHGADJsgmoN4BWyGJ PwQt1zOXqym5/3uhI0IDmNcF+Q9pFDyW/VSXHZz/HTnNxjU3kOhMbxpapLrCjV+fHu sgLqVD4Rqxisw== Message-ID: <7da224cd-fd9c-4c80-9a23-cb977420f50b@canonical.com> Date: Thu, 8 May 2025 00:52:55 -0700 Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] Wire up the lsm_manage_policy syscall To: Tetsuo Handa , =?UTF-8?Q?Maxime_B=C3=A9lair?= , Song Liu Cc: linux-security-module@vger.kernel.org, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, mic@digikod.net, kees@kernel.org, stephen.smalley.work@gmail.com, casey@schaufler-ca.com, takedakn@nttdata.co.jp, linux-api@vger.kernel.org, apparmor@lists.ubuntu.com, linux-kernel@vger.kernel.org References: <20250506143254.718647-1-maxime.belair@canonical.com> <20250506143254.718647-2-maxime.belair@canonical.com> <470689f0-223e-4d26-a919-8d48f383883b@I-love.SAKURA.ne.jp> Content-Language: en-US From: John Johansen Autocrypt: addr=john.johansen@canonical.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/7/25 15:04, Tetsuo Handa wrote: > On 2025/05/08 0:37, Maxime Bélair wrote: >> Again, each module decides which operations to expose through this syscall. In many cases >> the operation will still require CAP_SYS_ADMIN or a similar capability, so environments >> that choose this interface remain secure while gaining its advantages. > > If the interpretation of "flags" argument varies across LSMs, it sounds like ioctl()'s yes that does feel like ioctls(), on the other hand defining them at the LSM level won't offer LSMs flexibility making it so the syscall covers fewer use cases. I am not opposed to either, it just hashing out what people want, and what is acceptable. > "cmd" argument. Also, there is prctl() which can already carry string-ish parameters > without involving open(). Why can't we use prctl() instead of lsm_manage_policy() ? > prctl() can be used, I used it for the unprivileged policy demo. It has its own set of problems. While LSM policy could be associated with the process doing the load/replacement or what ever operation, it isn't necessarily tied to it. A lot of LSM policy is not process specific making prctl() a poor fit. prctl() requires allocating a global prctl() prctl() are already being filtered/controlled by LSMs making them a poort fit for use by an LSM in a stacking situation as it requires updating the policy of other LSMs on the system. Yes seccomp can filter the syscall but that still is an easier barrier to overcome than having to have instruction for how to allow your LSMs prctl() in multiple LSMs. Mickaël already argued the need for landlock to have syscalls. See https://lore.kernel.org/lkml/20200511192156.1618284-7-mic@digikod.net/ and the numerous iterations before that. Ideally those could have been LSM syscalls, with landlock leveraging them. AppArmor is getting to where it has similar needs to landlock. Yes we can use ioctls, prctls, netlink, the fs, etc. it doesn't mean that those are the best interfaces to do so, and ideally any interface we use will be of benefit to some other LSMs in the future.