[PATCH v20 02/23] LSM: Create and manage the lsmblob data structure.

[Paul Moore]

On Wed, Aug 26, 2020 at 11:03 AM Casey Schaufler <casey at schaufler-ca.com> wrote:
>
> When more than one security module is exporting data to
> audit and networking sub-systems a single 32 bit integer
> is no longer sufficient to represent the data. Add a
> structure to be used instead.
>
> The lsmblob structure is currently an array of
> u32 "secids". There is an entry for each of the
> security modules built into the system that would
> use secids if active. The system assigns the module
> a "slot" when it registers hooks. If modules are
> compiled in but not registered there will be unused
> slots.
>
> A new lsm_id structure, which contains the name
> of the LSM and its slot number, is created. There
> is an instance for each LSM, which assigns the name
> and passes it to the infrastructure to set the slot.
>
> The audit rules data is expanded to use an array of
> security module data rather than a single instance.
> Because IMA uses the audit rule functions it is
> affected as well.
>
> Acked-by: Stephen Smalley <sds at tycho.nsa.gov>
> Acked-by: Paul Moore <paul at paul-moore.com>
> Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
> ---
>  include/linux/audit.h               |  4 +-
>  include/linux/lsm_hooks.h           | 12 ++++-
>  include/linux/security.h            | 67 +++++++++++++++++++++++++--
>  kernel/auditfilter.c                | 24 +++++-----
>  kernel/auditsc.c                    | 12 ++---
>  security/apparmor/lsm.c             |  7 ++-
>  security/bpf/hooks.c                | 12 ++++-
>  security/commoncap.c                |  7 ++-
>  security/integrity/ima/ima_policy.c | 40 +++++++++++-----
>  security/loadpin/loadpin.c          |  8 +++-
>  security/lockdown/lockdown.c        |  7 ++-
>  security/safesetid/lsm.c            |  8 +++-
>  security/security.c                 | 72 ++++++++++++++++++++++++-----
>  security/selinux/hooks.c            |  8 +++-
>  security/smack/smack_lsm.c          |  7 ++-
>  security/tomoyo/tomoyo.c            |  8 +++-
>  security/yama/yama_lsm.c            |  7 ++-
>  17 files changed, 254 insertions(+), 56 deletions(-)

...

> diff --git a/include/linux/security.h b/include/linux/security.h
> index 0a0a03b36a3b..c91389d7aebc 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -131,6 +131,65 @@ enum lockdown_reason {
>
>  extern const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1];
>
> +/*
> + * Data exported by the security modules
> + *
> + * Any LSM that provides secid or secctx based hooks must be included.
> + */
> +#define LSMBLOB_ENTRIES ( \
> +       (IS_ENABLED(CONFIG_SECURITY_SELINUX) ? 1 : 0) + \
> +       (IS_ENABLED(CONFIG_SECURITY_SMACK) ? 1 : 0) + \
> +       (IS_ENABLED(CONFIG_SECURITY_APPARMOR) ? 1 : 0) + \
> +       (IS_ENABLED(CONFIG_BPF_LSM) ? 1 : 0))
> +
> +struct lsmblob {
> +       u32     secid[LSMBLOB_ENTRIES];
> +};
> +
> +#define LSMBLOB_INVALID                -1      /* Not a valid LSM slot number */
> +#define LSMBLOB_NEEDED         -2      /* Slot requested on initialization */
> +#define LSMBLOB_NOT_NEEDED     -3      /* Slot not requested */
> +
> +/**
> + * lsmblob_init - initialize an lsmblob structure.
> + * @blob: Pointer to the data to initialize
> + * @secid: The initial secid value
> + *
> + * Set all secid for all modules to the specified value.
> + */
> +static inline void lsmblob_init(struct lsmblob *blob, u32 secid)
> +{
> +       int i;
> +
> +       for (i = 0; i < LSMBLOB_ENTRIES; i++)
> +               blob->secid[i] = secid;
> +}

As I'm going through the v20 draft of these patches it occurs to me,
at least in the intermediate patches, that there is a pretty common
pattern involving lsmblob_init():

  lsmblob_init(blob, secid);
  func(blob, ...);

... would it make sense to have lsmblob_init() return *blob instead of
void?  It doesn't really matter too much, but it seems like it could
help cleanup some of the code:

  func(lsmblob_init(blob, secid), ...);

-- 
paul moore
www.paul-moore.com