linux-kernel - Re: [PATCH v1 7/8] LSM: Create lsm_module

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Message-ID: <CAHC9VhQMfAix=KqpWGNg_2cryBJHyiFTzURQ1YuD_0SY92ZHsA@mail.gmail.com>
Date:   Wed, 9 Nov 2022 22:17:52 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     casey.schaufler@...el.com, linux-security-module@...r.kernel.org,
        jmorris@...ei.org, keescook@...omium.org,
        john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, mic@...ikod.net
Subject: Re: [PATCH v1 7/8] LSM: Create lsm_module_list system call

On Wed, Nov 9, 2022 at 8:37 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
> On 11/9/2022 3:35 PM, Paul Moore wrote:
> > On Tue, Oct 25, 2022 at 2:48 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
> >> Create a system call to report the list of Linux Security Modules
> >> that are active on the system. The list is provided as an array
> >> of LSM ID numbers.
> >>
> >> The calling application can use this list determine what LSM
> >> specific actions it might take. That might include chosing an
> >> output format, determining required privilege or bypassing
> >> security module specific behavior.
> >>
> >> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> >> ---
> >>  include/linux/syscalls.h |  1 +
> >>  kernel/sys_ni.c          |  1 +
> >>  security/lsm_syscalls.c  | 38 ++++++++++++++++++++++++++++++++++++++
> >>  3 files changed, 40 insertions(+)
> > ..
> >
> >> diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
> >> index da0fab7065e2..cd5db370b974 100644
> >> --- a/security/lsm_syscalls.c
> >> +++ b/security/lsm_syscalls.c
> >> @@ -154,3 +154,41 @@ SYSCALL_DEFINE3(lsm_self_attr,
> >>         kfree(final);
> >>         return rc;
> >>  }
> >> +
> >> +/**
> >> + * lsm_module_list - Return a list of the active security modules
> >> + * @ids: the LSM module ids
> >> + * @size: size of @ids, updated on return
> >> + * @flags: reserved for future use, must be zero
> >> + *
> >> + * Returns a list of the active LSM ids. On success this function
> >> + * returns the number of @ids array elements. This value may be zero
> >> + * if there are no LSMs active. If @size is insufficient to contain
> >> + * the return data -E2BIG is returned and @size is set to the minimum
> >> + * required size. In all other cases a negative value indicating the
> >> + * error is returned.
> >> + */
> > Let's make a promise that for this syscall we will order the LSM IDs
> > in the array in the same order as which they are configured/executed.
>
> Sure. Order registered, which can vary, as opposed to LSM ID order,
> which cannot. That could be important to ensure that applications
> that enforce the same policy as the kernel will hit the checks in
> the same order as the kernel. That's how it is coded. It needs to
> be documented.

Yep.  One of the big reasons for documenting it this way is to ensure
that we define the order as part of the API.

-- 
paul-moore.com