Re: [PATCH 2/9] security: Add hooks to rule on setting a watch [ver #5]

[Stephen Smalley <sds@tycho.nsa.gov>]

On 6/28/19 11:48 AM, David Howells wrote:
> Add security hooks that will allow an LSM to rule on whether or not a watch
> may be set.  More than one hook is required as the watches watch different
> types of object.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Casey Schaufler <casey@schaufler-ca.com>
> cc: Stephen Smalley <sds@tycho.nsa.gov>
> cc: linux-security-module@vger.kernel.org
> ---
> 
>   include/linux/lsm_hooks.h |   22 ++++++++++++++++++++++
>   include/linux/security.h  |   15 +++++++++++++++
>   security/security.c       |   13 +++++++++++++
>   3 files changed, 50 insertions(+)
> 
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 47f58cfb6a19..f9d31f6445e4 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1413,6 +1413,20 @@
>    *	@ctx is a pointer in which to place the allocated security context.
>    *	@ctxlen points to the place to put the length of @ctx.
>    *
> + * Security hooks for the general notification queue:
> + *
> + * @watch_key:
> + *	Check to see if a process is allowed to watch for event notifications
> + *	from a key or keyring.
> + *	@watch: The watch object
> + *	@key: The key to watch.
> + *
> + * @watch_devices:
> + *	Check to see if a process is allowed to watch for event notifications
> + *	from devices (as a global set).
> + *	@watch: The watch object

It is difficult to evaluate these without at least one implementation of 
each hook.  I am unclear as to how any security module would use the 
watch argument, since it has no security field/blob and does not appear 
to contain any information that would be relevant to deciding whether or 
not to permit the watch to be set.

> + *
> + *
>    * Security hooks for using the eBPF maps and programs functionalities through
>    * eBPF syscalls.
>    *
> @@ -1688,6 +1702,10 @@ union security_list_options {
>   	int (*inode_notifysecctx)(struct inode *inode, void *ctx, u32 ctxlen);
>   	int (*inode_setsecctx)(struct dentry *dentry, void *ctx, u32 ctxlen);
>   	int (*inode_getsecctx)(struct inode *inode, void **ctx, u32 *ctxlen);
> +#ifdef CONFIG_WATCH_QUEUE
> +	int (*watch_key)(struct watch *watch, struct key *key);
> +	int (*watch_devices)(struct watch *watch);
> +#endif /* CONFIG_WATCH_QUEUE */
>   
>   #ifdef CONFIG_SECURITY_NETWORK
>   	int (*unix_stream_connect)(struct sock *sock, struct sock *other,
> @@ -1964,6 +1982,10 @@ struct security_hook_heads {
>   	struct hlist_head inode_notifysecctx;
>   	struct hlist_head inode_setsecctx;
>   	struct hlist_head inode_getsecctx;
> +#ifdef CONFIG_WATCH_QUEUE
> +	struct hlist_head watch_key;
> +	struct hlist_head watch_devices;
> +#endif /* CONFIG_WATCH_QUEUE */
>   #ifdef CONFIG_SECURITY_NETWORK
>   	struct hlist_head unix_stream_connect;
>   	struct hlist_head unix_may_send;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 659071c2e57c..540863678355 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -57,6 +57,7 @@ struct mm_struct;
>   struct fs_context;
>   struct fs_parameter;
>   enum fs_value_type;
> +struct watch;
>   
>   /* Default (no) options for the capable function */
>   #define CAP_OPT_NONE 0x0
> @@ -392,6 +393,10 @@ void security_inode_invalidate_secctx(struct inode *inode);
>   int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
>   int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
>   int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
> +#ifdef CONFIG_WATCH_QUEUE
> +int security_watch_key(struct watch *watch, struct key *key);
> +int security_watch_devices(struct watch *watch);
> +#endif /* CONFIG_WATCH_QUEUE */
>   #else /* CONFIG_SECURITY */
>   
>   static inline int call_lsm_notifier(enum lsm_event event, void *data)
> @@ -1204,6 +1209,16 @@ static inline int security_inode_getsecctx(struct inode *inode, void **ctx, u32
>   {
>   	return -EOPNOTSUPP;
>   }
> +#ifdef CONFIG_WATCH_QUEUE
> +static inline int security_watch_key(struct watch *watch, struct key *key)
> +{
> +	return 0;
> +}
> +static inline int security_watch_devices(struct watch *watch)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_WATCH_QUEUE */
>   #endif	/* CONFIG_SECURITY */
>   
>   #ifdef CONFIG_SECURITY_NETWORK
> diff --git a/security/security.c b/security/security.c
> index 613a5c00e602..2c9919226ad1 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1917,6 +1917,19 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
>   }
>   EXPORT_SYMBOL(security_inode_getsecctx);
>   
> +#ifdef CONFIG_WATCH_QUEUE
> +int security_watch_key(struct watch *watch, struct key *key)
> +{
> +	return call_int_hook(watch_key, 0, watch, key);
> +}
> +
> +int security_watch_devices(struct watch *watch)
> +{
> +	return call_int_hook(watch_devices, 0, watch);
> +}
> +
> +#endif /* CONFIG_WATCH_QUEUE */
> +
>   #ifdef CONFIG_SECURITY_NETWORK
>   
>   int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)
>