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Message-ID: <20240718.yieCh6miu9en@digikod.net> Date: Thu, 18 Jul 2024 17:35:36 +0200 From: Mickaël Salaün <mic@...ikod.net> To: James Bottomley <James.Bottomley@...senpartnership.com> Cc: Jeff Xu <jeffxu@...gle.com>, Al Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Kees Cook <keescook@...omium.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Paul Moore <paul@...l-moore.com>, Theodore Ts'o <tytso@....edu>, Alejandro Colomar <alx@...nel.org>, Aleksa Sarai <cyphar@...har.com>, Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>, Casey Schaufler <casey@...aufler-ca.com>, Christian Heimes <christian@...hon.org>, Dmitry Vyukov <dvyukov@...gle.com>, Eric Biggers <ebiggers@...nel.org>, Eric Chiang <ericchiang@...gle.com>, Fan Wu <wufan@...ux.microsoft.com>, Florian Weimer <fweimer@...hat.com>, Geert Uytterhoeven <geert@...ux-m68k.org>, James Morris <jamorris@...ux.microsoft.com>, Jan Kara <jack@...e.cz>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, Jordan R Abrahams <ajordanr@...gle.com>, Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>, Luca Boccassi <bluca@...ian.org>, Luis Chamberlain <mcgrof@...nel.org>, "Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>, Matt Bobrowski <mattbobrowski@...gle.com>, Matthew Garrett <mjg59@...f.ucam.org>, Matthew Wilcox <willy@...radead.org>, Miklos Szeredi <mszeredi@...hat.com>, Mimi Zohar <zohar@...ux.ibm.com>, Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>, Scott Shell <scottsh@...rosoft.com>, Shuah Khan <shuah@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>, Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>, Thibaut Sautereau <thibaut.sautereau@....gouv.fr>, Vincent Strubel <vincent.strubel@....gouv.fr>, Xiaoming Ni <nixiaoming@...wei.com>, Yin Fengwei <fengwei.yin@...el.com>, 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, Elliott Hughes <enh@...gle.com> Subject: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2) On Thu, Jul 18, 2024 at 09:03:36AM -0400, James Bottomley wrote: > On Thu, 2024-07-18 at 14:24 +0200, Mickaël Salaün wrote: > > On Wed, Jul 17, 2024 at 07:08:17PM -0700, Jeff Xu wrote: > > > On Wed, Jul 17, 2024 at 3:01 AM Mickaël Salaün <mic@...ikod.net> > > > wrote: > > > > On Tue, Jul 16, 2024 at 11:33:55PM -0700, Jeff Xu wrote: > [...] > > > > > I'm still thinking execveat(AT_CHECK) vs faccessat(AT_CHECK) > > > > > in different use cases: > > > > > > > > > > execveat clearly has less code change, but that also means: we > > > > > can't add logic specific to exec (i.e. logic that can't be > > > > > applied to config) for this part (from do_execveat_common to > > > > > security_bprm_creds_for_exec) in future. This would require > > > > > some agreement/sign-off, I'm not sure from whom. > > > > > > > > I'm not sure to follow. We could still add new flags, but for now > > > > I don't see use cases. This patch series is not meant to handle > > > > all possible "trust checks", only executable code, which makes > > > > sense for the kernel. > > > > > > > I guess the "configfile" discussion is where I get confused, at one > > > point, I think this would become a generic "trust checks" api for > > > everything related to "generating executable code", e.g. > > > javascript, java code, and more. We will want to clearly define the > > > scope of execveat(AT_CHECK) > > > > The line between data and code is blurry. For instance, a > > configuration file can impact the execution flow of a program. So, > > where to draw the line? > > Having a way to have config files part of the trusted envelope, either > by signing or measurement would be really useful. The current standard > distro IMA deployment is signed executables, but not signed config > because it's hard to construct a policy that doesn't force the signing > of too many extraneous files (and files which might change often). > > > It might makes sense to follow the kernel and interpreter semantic: > > if a file can be executed by the kernel (e.g. ELF binary, file > > containing a shebang, or just configured with binfmt_misc), then this > > should be considered as executable code. This applies to Bash, > > Python, Javascript, NodeJS, PE, PHP... However, we can also make a > > picture executable with binfmt_misc. So, again, where to draw the > > line? > > Possibly by making open for config an indication executables can give? > I'm not advocating doing it in this patch, but if we had an open for > config indication, the LSMs could do much finer grained policy, > especially if they knew which executable was trying to open the config > file. It would allow things like an IMA policy saying if a signed > executable is opening a config file, then that file must also be > signed. Checking configuration could be a next step, but not with this patch series. FYI, the previous version was a (too) generic syscall: https://lore.kernel.org/all/20220104155024.48023-1-mic@digikod.net/ One of the main concern was alignment with kernel semantic. For now, let's focus on script execution control. > > James >
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