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Message-ID: <a48145770780d36e90f28f1526805a7292eb74f6.camel@linux.ibm.com> Date: Thu, 10 Sep 2020 14:08:56 -0400 From: Mimi Zohar <zohar@...ux.ibm.com> To: Mickaël Salaün <mic@...ikod.net>, Matthew Wilcox <willy@...radead.org> Cc: linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>, Alexei Starovoitov <ast@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, 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>, Daniel Borkmann <daniel@...earbox.net>, 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>, 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>, Matthew Garrett <mjg59@...gle.com>, Michael Kerrisk <mtk.manpages@...il.com>, Miklos Szeredi <mszeredi@...hat.com>, Philippe Trébuchet <philippe.trebuchet@....gouv.fr>, Scott Shell <scottsh@...rosoft.com>, Sean Christopherson <sean.j.christopherson@...el.com>, Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>, Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Thibaut Sautereau <thibaut.sautereau@...p-os.org>, Vincent Strubel <vincent.strubel@....gouv.fr>, kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org, linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [RFC PATCH v9 0/3] Add introspect_access(2) (was O_MAYEXEC) On Thu, 2020-09-10 at 19:21 +0200, Mickaël Salaün wrote: > On 10/09/2020 19:04, Matthew Wilcox wrote: > > On Thu, Sep 10, 2020 at 06:46:09PM +0200, Mickaël Salaün wrote: > >> This ninth patch series rework the previous AT_INTERPRETED and O_MAYEXEC > >> series with a new syscall: introspect_access(2) . Access check are now > >> only possible on a file descriptor, which enable to avoid possible race > >> conditions in user space. > > > > But introspection is about examining _yourself_. This isn't about > > doing that. It's about doing ... something ... to a script that you're > > going to execute. If the script were going to call the syscall, then > > it might be introspection. Or if the interpreter were measuring itself, > > that would be introspection. But neither of those would be useful things > > to do, because an attacker could simply avoid doing them. > Michael, is the confusion here that IMA isn't measuring anything, but verifying the integrity of the file? The usecase, from an IMA perspective, is enforcing a system wide policy requiring everything executed to be signed. In this particular use case, the interpreter is asking the kernel if the script is signed with a permitted key. The signature may be an IMA signature or an EVM portable and immutable signature, based on policy. > Picking a good name other than "access" (or faccessat2) is not easy. The > idea with introspect_access() is for the calling task to ask the kernel > if this task should allows to do give access to a kernel resource which > is already available to this task. In this sense, we think that > introspection makes sense because it is the choice of the task to allow > or deny an access. > > > > > So, bad name. What might be better? sys_security_check()? > > sys_measure()? sys_verify_fd()? I don't know. > > > > "security_check" looks quite broad, "measure" doesn't make sense here, > "verify_fd" doesn't reflect that it is an access check. Yes, not easy, > but if this is the only concern we are on the good track. :) Maybe replacing the term "measure" with "integrity", but rather than "integrity_check", something along the lines of fgetintegrity, freadintegrity, fcheckintegrity. Mimi > > > Other ideas: > - interpret_access (mainly, but not only, for interpreters) > - indirect_access > - may_access > - faccessat3
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