[PATCH v3 10/24] Use lsmblob in security_ipc_getsecid

[Kees Cook]

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.

-- 
Kees Cook