Date: Mon, 11 Oct 2021 14:07:55 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Mickaël Salaün <mic@...ikod.net> Cc: Al Viro <viro@...iv.linux.org.uk>, Aleksa Sarai <cyphar@...har.com>, Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>, Casey Schaufler <casey@...aufler-ca.com>, Christian Brauner <christian.brauner@...ntu.com>, Christian Heimes <christian@...hon.org>, Deven Bowers <deven.desai@...ux.microsoft.com>, Dmitry Vyukov <dvyukov@...gle.com>, Eric Biggers <ebiggers@...nel.org>, Eric Chiang <ericchiang@...gle.com>, Florian Weimer <fweimer@...hat.com>, Geert Uytterhoeven <geert@...ux-m68k.org>, James Morris <jmorris@...ei.org>, Jan Kara <jack@...e.cz>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>, Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>, "Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>, Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>, Miklos Szeredi <mszeredi@...hat.com>, Mimi Zohar <zohar@...ux.ibm.com>, Paul Moore <paul@...l-moore.com>, Philippe Trébuchet <philippe.trebuchet@....gouv.fr>, Scott Shell <scottsh@...rosoft.com>, Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>, Thibaut Sautereau <thibaut.sautereau@....gouv.fr>, Vincent Strubel <vincent.strubel@....gouv.fr>, kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org Subject: Re: [PATCH v14 0/3] Add trusted_for(2) (was O_MAYEXEC) On Mon, 11 Oct 2021 10:47:04 +0200 Mickaël Salaün <mic@...ikod.net> wrote: > > On 10/10/2021 23:48, Andrew Morton wrote: > > On Fri, 8 Oct 2021 12:48:37 +0200 Mickaël Salaün <mic@...ikod.net> wrote: > > > >> The final goal of this patch series is to enable the kernel to be a > >> global policy manager by entrusting processes with access control at > >> their level. To reach this goal, two complementary parts are required: > >> * user space needs to be able to know if it can trust some file > >> descriptor content for a specific usage; > >> * and the kernel needs to make available some part of the policy > >> configured by the system administrator. > > > > Apologies if I missed this... > > > > It would be nice to see a description of the proposed syscall interface > > in these changelogs! Then a few questions I have will be answered... > > I described this syscall and it's semantic in the first patch in > Documentation/admin-guide/sysctl/fs.rst Well, kinda. It didn't explain why the `usage' and `flags' arguments exist and what are the plans for them. > Do you want me to copy-paste this content in the cover letter? That would be best please. It's basically the most important thing when reviewing the implementation. > > > > long trusted_for(const int fd, > > const enum trusted_for_usage usage, > > const u32 flags) > > > > - `usage' must be equal to TRUSTED_FOR_EXECUTION, so why does it > > exist? Some future modes are planned? Please expand on this. > > Indeed, the current use case is to check if the kernel would allow > execution of a file. But as Florian pointed out, we may want to add more > context in the future, e.g. to enforce signature verification, to check > if this is a legitimate (system) library, to check if the file is > allowed to be used as (trusted) configuration… > > > > > - `flags' is unused (must be zero). So why does it exist? What are > > the plans here? > > This is mostly to follow syscall good practices for extensibility. It > could be used in combination with the usage argument (which defines the > user space semantic), e.g. to check for extra properties such as > cryptographic or integrity requirements, origin of the file… > > > > > - what values does the syscall return and what do they mean? > > > > It returns 0 on success, or -EACCES if the kernel policy denies the > specified usage. And please document all of this in the changelog also.
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