[PATCH v3 10/24] Use lsmblob in security_ipc_getsecid

[Casey Schaufler]

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.