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Message-ID: <1c3874c1-870a-ac60-03e6-2c16d49e185b@schaufler-ca.com>
Date: Tue, 25 May 2021 16:52:10 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Mickaël Salaün <mic@...ikod.net>,
casey.schaufler@...el.com, jmorris@...ei.org,
linux-security-module@...r.kernel.org, selinux@...r.kernel.org
Cc: linux-audit@...hat.com, keescook@...omium.org,
john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
paul@...l-moore.com, sds@...ho.nsa.gov,
linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v26 02/25] LSM: Add the lsmblob data structure.
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@...ho.nsa.gov>
>> Acked-by: Paul Moore <paul@...l-moore.com>
>> Acked-by: John Johansen <john.johansen@...onical.com>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>> Cc: <bpf@...r.kernel.org>
>> Cc: linux-audit@...hat.com
>> Cc: linux-security-module@...r.kernel.org
>> Cc: selinux@...r.kernel.org
>> To: Mimi Zohar <zohar@...ux.ibm.com>
>> To: Mickaël Salaün <mic@...ux.microsoft.com>
>> ---
>> 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);
>> }
>>
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