Re: [PATCH v26 02/25] LSM: Add the lsmblob data structure.

[Mickaël Salaün]

I like this design but there is an issue with Landlock though, see below.

On 13/05/2021 22:07, Casey Schaufler 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@xxxxxxxxxxxxx>
> Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
> Acked-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> Cc: <bpf@xxxxxxxxxxxxxxx>
> Cc: linux-audit@xxxxxxxxxx
> Cc: linux-security-module@xxxxxxxxxxxxxxx
> Cc: selinux@xxxxxxxxxxxxxxx
> To: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> To: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
> ---
>  include/linux/audit.h               |  4 +-
>  include/linux/lsm_hooks.h           | 12 ++++-
>  include/linux/security.h            | 67 +++++++++++++++++++++++++--
>  kernel/auditfilter.c                | 24 +++++-----
>  kernel/auditsc.c                    | 13 +++---
>  security/apparmor/lsm.c             |  7 ++-
>  security/bpf/hooks.c                | 12 ++++-
>  security/commoncap.c                |  7 ++-
>  security/integrity/ima/ima_policy.c | 40 +++++++++++-----
>  security/landlock/cred.c            |  2 +-
>  security/landlock/fs.c              |  2 +-
>  security/landlock/ptrace.c          |  2 +-
>  security/landlock/setup.c           |  4 ++
>  security/landlock/setup.h           |  1 +
>  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 ++-
>  22 files changed, 262 insertions(+), 60 deletions(-)
> 

[...]

> diff --git a/security/landlock/setup.c b/security/landlock/setup.c
> index f8e8e980454c..4a12666a4090 100644
> --- a/security/landlock/setup.c
> +++ b/security/landlock/setup.c
> @@ -23,6 +23,10 @@ struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = {
>  	.lbs_superblock = sizeof(struct landlock_superblock_security),
>  };
>  
> +struct lsm_id landlock_lsmid __lsm_ro_after_init = {
> +	.lsm = LANDLOCK_NAME,

It is missing: .slot = LSMBLOB_NEEDED,

You can run the Landlock tests please?
make -C tools/testing/selftests TARGETS=landlock gen_tar
tar -xf kselftest.tar.gz && ./run_kselftest.sh


> +};
> +
>  static int __init landlock_init(void)
>  {
>  	landlock_add_cred_hooks();

[...]

> diff --git a/security/security.c b/security/security.c
> index e12a7c463468..a3276deb1b8a 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -344,6 +344,7 @@ static void __init ordered_lsm_init(void)
>  	init_debug("sock blob size       = %d\n", blob_sizes.lbs_sock);
>  	init_debug("superblock blob size = %d\n", blob_sizes.lbs_superblock);
>  	init_debug("task blob size       = %d\n", blob_sizes.lbs_task);
> +	init_debug("lsmblob size         = %zu\n", sizeof(struct lsmblob));
>  
>  	/*
>  	 * Create any kmem_caches needed for blobs
> @@ -471,21 +472,36 @@ static int lsm_append(const char *new, char **result)
>  	return 0;
>  }
>  
> +/*
> + * Current index to use while initializing the lsmblob secid list.
> + */
> +static int lsm_slot __lsm_ro_after_init;
> +
>  /**
>   * security_add_hooks - Add a modules hooks to the hook lists.
>   * @hooks: the hooks to add
>   * @count: the number of hooks to add
> - * @lsm: the name of the security module
> + * @lsmid: the identification information for the security module
>   *
>   * Each LSM has to register its hooks with the infrastructure.
> + * If the LSM is using hooks that export secids allocate a slot
> + * for it in the lsmblob.
>   */
>  void __init security_add_hooks(struct security_hook_list *hooks, int count,
> -				char *lsm)
> +			       struct lsm_id *lsmid)
>  {
>  	int i;
>  

Could you add a WARN_ON(!lsmid->slot || !lsmid->name) here?


> +	if (lsmid->slot == LSMBLOB_NEEDED) {
> +		if (lsm_slot >= LSMBLOB_ENTRIES)
> +			panic("%s Too many LSMs registered.\n", __func__);
> +		lsmid->slot = lsm_slot++;
> +		init_debug("%s assigned lsmblob slot %d\n", lsmid->lsm,
> +			   lsmid->slot);
> +	}
> +
>  	for (i = 0; i < count; i++) {
> -		hooks[i].lsm = lsm;
> +		hooks[i].lsmid = lsmid;
>  		hlist_add_tail_rcu(&hooks[i].list, hooks[i].head);
>  	}
>