linux-kernel - Re: [PATCH v5 5/8] LSM: Create lsm_module

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Message-ID: <CAHC9VhQn0QxYW7wZ4H14AYNMik0AnojB6qmTCn2Swkep956WMg@mail.gmail.com>
Date:   Thu, 12 Jan 2023 16:43:22 -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 v5 5/8] LSM: Create lsm_module_list system call

On Wed, Jan 11, 2023 at 8:39 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
> On 1/11/2023 1:07 PM, Paul Moore wrote:
> > On Mon, Jan 9, 2023 at 1:09 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>
> >> ---
> >>  Documentation/userspace-api/lsm.rst |  3 +++
> >>  include/linux/syscalls.h            |  1 +
> >>  kernel/sys_ni.c                     |  1 +
> >>  security/lsm_syscalls.c             | 41 +++++++++++++++++++++++++++++
> >>  4 files changed, 46 insertions(+)
> > ..
> >
> >> diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
> >> index 55e8bf61ac8a..92af1fcaa654 100644
> >> --- a/security/lsm_syscalls.c
> >> +++ b/security/lsm_syscalls.c
> >> @@ -180,3 +180,44 @@ SYSCALL_DEFINE3(lsm_get_self_attr,
> >>         kfree(final);
> >>         return rc;
> >>  }
> >> +
> >> +/**
> >> + * sys_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.
> >> + */
> >> +SYSCALL_DEFINE3(lsm_module_list,
> >> +               u32 __user *, ids,
> >> +               size_t __user *, size,
> >> +               u64, flags)
> >> +{
> >> +       size_t total_size = lsm_active_cnt * sizeof(*ids);
> >> +       size_t usize;
> >> +       int i;
> >> +
> >> +       if (flags)
> >> +               return -EINVAL;
> >> +
> >> +       if (get_user(usize, size))
> >> +               return -EFAULT;
> >> +
> >> +       if (put_user(total_size, size) != 0)
> >> +               return -EFAULT;
> >> +
> >> +       if (usize < total_size)
> >> +               return -E2BIG;
> >> +
> >> +       for (i = 0; i < lsm_active_cnt; i++)
> >> +               if (put_user(lsm_idlist[i]->id, ids++))
> >> +                       return -EFAULT;
> >> +
> >> +       return lsm_active_cnt;
> >> +}
> > Similar to my comments in 4/8, I would probably create a new LSM hook
> > for this syscall so that the lsm_ctx is passed through the LSM layer
> > directly to the target LSM:
> >
> >   int security_sys_setselfattr(u64 attr, struct lsm_ctx __user *ctx,
> > size_t len);
>
> That seems like a whole lot of work when you can just look it up
> in an existing table.

D'oh!  Sorry, this comment was intended for patch 6/8, the
lsm_set_self_attr() syscall patch.  I agree, it would be very silly to
have a dedicated hook for lsm_module_list() :)

-- 
paul-moore.com