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

[Casey Schaufler]

On 5/22/2021 1:39 AM, Mickaël Salaün wrote:
> 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,

Sorry for the delay.

Landlock does not provide any of the hooks that use a struct lsmblob.
That would be secid_to_secctx, secctx_to_secid, inode_getsecid,
cred_getsecid, kernel_act_as task_getsecid_subj task_getsecid_obj and
ipc_getsecid. Setting .slot = LSMBLOB_NEEDED indicates that the LSM
uses a slot in struct lsmblob. Landlock does not need a slot.

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

Sure. I'll add them to my routine.

>
>
>> +};
>> +
>>  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?

Yes. That's reasonable.

>
>
>> +	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);
>>  	}
>>