[PATCH v3 10/24] Use lsmblob in security_ipc_getsecid

[Casey Schaufler]

On 6/24/2019 9:39 AM, Casey Schaufler wrote:
> On 6/22/2019 3:48 PM, Kees Cook wrote:
>> On Fri, Jun 21, 2019 at 11:52:19AM -0700, Casey Schaufler wrote:
>>> There may be more than one LSM that provides IPC data
>>> for auditing. Change security_ipc_getsecid() to fill in
>>> a lsmblob structure instead of the u32 secid. The
>>> audit data structure containing the secid will be updated
>>> later, so there is a bit of scaffolding here.
>>>
>>> Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
>> Reviewed-by: Kees Cook <keescook at chromium.org>
>>
>> One thought below...
>>
>>> ---
>>>  include/linux/security.h | 7 ++++---
>>>  kernel/auditsc.c         | 5 ++++-
>>>  security/security.c      | 9 ++++++---
>>>  3 files changed, 14 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/linux/security.h b/include/linux/security.h
>>> index c6cddeff8a17..0d5e172341fc 100644
>>> --- a/include/linux/security.h
>>> +++ b/include/linux/security.h
>>> @@ -413,7 +413,7 @@ int security_task_prctl(int option, unsigned long arg2, unsigned long arg3,
>>>  			unsigned long arg4, unsigned long arg5);
>>>  void security_task_to_inode(struct task_struct *p, struct inode *inode);
>>>  int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag);
>>> -void security_ipc_getsecid(struct kern_ipc_perm *ipcp, u32 *secid);
>>> +void security_ipc_getsecid(struct kern_ipc_perm *ipcp, struct lsmblob *blob);
>>>  int security_msg_msg_alloc(struct msg_msg *msg);
>>>  void security_msg_msg_free(struct msg_msg *msg);
>>>  int security_msg_queue_alloc(struct kern_ipc_perm *msq);
>>> @@ -1098,9 +1098,10 @@ static inline int security_ipc_permission(struct kern_ipc_perm *ipcp,
>>>  	return 0;
>>>  }
>>>  
>>> -static inline void security_ipc_getsecid(struct kern_ipc_perm *ipcp, u32 *secid)
>>> +static inline void security_ipc_getsecid(struct kern_ipc_perm *ipcp,
>>> +					 struct lsmblob *blob)
>>>  {
>>> -	*secid = 0;
>>> +	lsmblob_init(blob, 0);
>>>  }
>>>  
>>>  static inline int security_msg_msg_alloc(struct msg_msg *msg)
>>> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
>>> index d31914088a82..148733ec3c72 100644
>>> --- a/kernel/auditsc.c
>>> +++ b/kernel/auditsc.c
>>> @@ -2268,11 +2268,14 @@ void __audit_mq_getsetattr(mqd_t mqdes, struct mq_attr *mqstat)
>>>  void __audit_ipc_obj(struct kern_ipc_perm *ipcp)
>>>  {
>>>  	struct audit_context *context = audit_context();
>>> +	struct lsmblob blob;
>>>  	context->ipc.uid = ipcp->uid;
>>>  	context->ipc.gid = ipcp->gid;
>>>  	context->ipc.mode = ipcp->mode;
>>>  	context->ipc.has_perm = 0;
>>> -	security_ipc_getsecid(ipcp, &context->ipc.osid);
>>> +	security_ipc_getsecid(ipcp, &blob);
>>> +	/* scaffolding on the [0] - change "osid" to a lsmblob */
>>> +	context->ipc.osid = blob.secid[0];
>>>  	context->type = AUDIT_IPC;
>>>  }
>>>  
>>> diff --git a/security/security.c b/security/security.c
>>> index 5ab07631df75..d55f01041f05 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -1812,10 +1812,13 @@ int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag)
>>>  	return call_int_hook(ipc_permission, 0, ipcp, flag);
>>>  }
>>>  
>>> -void security_ipc_getsecid(struct kern_ipc_perm *ipcp, u32 *secid)
>>> +void security_ipc_getsecid(struct kern_ipc_perm *ipcp, struct lsmblob *blob)
>>>  {
>>> -	*secid = 0;
>>> -	call_void_hook(ipc_getsecid, ipcp, secid);
>>> +	struct security_hook_list *hp;
>>> +
>>> +	lsmblob_init(blob, 0);
>>> +	hlist_for_each_entry(hp, &security_hook_heads.ipc_getsecid, list)
>>> +		hp->hook.ipc_getsecid(ipcp, &blob->secid[hp->slot]);
>> Just for sanity when using hp->slot, it might be good to do something
>> like this in the places it gets used. Like for here:
>>
>> 	if (!WARN_ON(hp->slot < 0 || hp->slot >= LSMBLOB_COUNT))
>> 		hp->hook.ipc_getsecid(ipcp, &blob->secid[hp->slot]);
>>
>> This _should_ be overkill, but since lists of hooks that trigger slot
>> assignment is hardcoded, it seems nice to cover any future problems or
>> mismatches.
> How about a CONFIG_LSM_SLOT_CHECK around a function lsm_slot_check()?
> If configured, it does the WARN_ON, and if not it's a static inline
> true return. As you say, it's probably overkill, but it would be available
> for the paranoid/debug/bringup situation.

... or maybe it would be better if security_add_hooks() had an
explicit parameter whereby an LSM can tell the infrastructure that
it wants a slot. The only future problems would come if the LSM
writer got the parameter wrong or if secid dependence got added
to an existing interface and a LSM that didn't used to need a 
slot suddenly did. I don't see either of those as compelling.