Re: [PATCH v3 2/9] LSM: Identify the process attributes for each module

["Mickaël Salaün" <mic@digikod.net>]

On 23/11/2022 21:15, Casey Schaufler wrote:
> Add an integer member "attrs_used" to the struct lsm_id which
> identifies the API related data associated with each security
> module. The initial set of features maps to information that
> has traditionaly been available in /proc/self/attr. They are
> documented in a new userspace-api file.
> 
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> ---
>   Documentation/userspace-api/index.rst |  1 +
>   Documentation/userspace-api/lsm.rst   | 55 +++++++++++++++++++++++++++
>   include/linux/lsm_hooks.h             |  2 +
>   include/uapi/linux/lsm.h              | 12 ++++++
>   security/apparmor/lsm.c               |  1 +
>   security/selinux/hooks.c              |  2 +
>   security/smack/smack_lsm.c            |  1 +
>   7 files changed, 74 insertions(+)
>   create mode 100644 Documentation/userspace-api/lsm.rst
> 
> diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
> index c78da9ce0ec4..6feff0fcd88f 100644
> --- a/Documentation/userspace-api/index.rst
> +++ b/Documentation/userspace-api/index.rst
> @@ -30,6 +30,7 @@ place where this information is gathered.
>      sysfs-platform_profile
>      vduse
>      futex2
> +   lsm
>   
>   .. only::  subproject and html
>   
> diff --git a/Documentation/userspace-api/lsm.rst b/Documentation/userspace-api/lsm.rst
> new file mode 100644
> index 000000000000..6ddf5506110b
> --- /dev/null
> +++ b/Documentation/userspace-api/lsm.rst
> @@ -0,0 +1,55 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +.. Copyright (C) 2022 Casey Schaufler <casey@schaufler-ca.com>
> +.. Copyright (C) 2022 Intel Corporation
> +
> +=====================================
> +Linux Security Modules
> +=====================================
> +
> +:Author: Casey Schaufler
> +:Date: November 2022
> +
> +Linux security modules (LSM) provide a mechanism to implement
> +additional access controls to the Linux security policies.
> +
> +The various security modules may support any of these attributes:
> +
> +``LSM_ATTR_CURRENT`` is the current, active security context of the
> +process.
> +The proc filesystem provides this value in ``/proc/self/attr/current``.
> +This is supported by the SELinux, Smack and AppArmor security modules.
> +Smack also provides this value in ``/proc/self/attr/smack/current``.
> +AppArmor also provides this value in ``/proc/self/attr/apparmor/current``.
> +
> +``LSM_ATTR_EXEC`` is the security context of the process at the time the
> +current image was executed.
> +The proc filesystem provides this value in ``/proc/self/attr/exec``.
> +This is supported by the SELinux and AppArmor security modules.
> +AppArmor also provides this value in ``/proc/self/attr/apparmor/exec``.
> +
> +``LSM_ATTR_FSCREATE`` is the security context of the process used when
> +creating file system objects.
> +The proc filesystem provides this value in ``/proc/self/attr/fscreate``.
> +This is supported by the SELinux security module.
> +
> +``LSM_ATTR_KEYCREATE`` is the security context of the process used when
> +creating key objects.
> +The proc filesystem provides this value in ``/proc/self/attr/keycreate``.
> +This is supported by the SELinux security module.
> +
> +``LSM_ATTR_PREV`` is the security context of the process at the time the
> +current security context was set.
> +The proc filesystem provides this value in ``/proc/self/attr/prev``.
> +This is supported by the SELinux and AppArmor security modules.
> +AppArmor also provides this value in ``/proc/self/attr/apparmor/prev``.
> +
> +``LSM_ATTR_SOCKCREATE`` is the security context of the process used when
> +creating socket objects.
> +The proc filesystem provides this value in ``/proc/self/attr/sockcreate``.
> +This is supported by the SELinux security module.
> +
> +Additional documentation
> +========================
> +
> +* Documentation/security/lsm.rst
> +* Documentation/security/lsm-development.rst
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index d306db1044d1..7e88acc37a29 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1606,12 +1606,14 @@ struct security_hook_heads {
>    * struct lsm_id - identify a Linux Security Module.
>    * @lsm: Name of the LSM. Must be approved by the LSM maintainers.
>    * @id: LSM ID number from uapi/linux/lsm.h
> + * @attrs_used: Which attributes this LSM supports.
>    *
>    * Contains the information that identifies the LSM.
>    */
>   struct lsm_id {
>   	const u8	*lsm;
>   	u32		id;
> +	u64		attrs_used;

I'd prefer this field to be part of the previous patch. This doesn't 
change much but it is to highlight that the struct lsm_id size should 
not change unless properly handled by userspace.


>   };
>   
>   /*
> diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h
> index 47791c330cbf..8e9124bf622c 100644
> --- a/include/uapi/linux/lsm.h
> +++ b/include/uapi/linux/lsm.h
> @@ -29,4 +29,16 @@
>   #define LSM_ID_BPF		110
>   #define LSM_ID_LANDLOCK		111
>   
> +/*
> + * LSM_ATTR_XXX values identify the /proc/.../attr entry that the
> + * context represents. Not all security modules provide all of these
> + * values. Some security modules provide none of them.
> + */
> +#define LSM_ATTR_CURRENT	0x0001
> +#define LSM_ATTR_EXEC		0x0002
> +#define LSM_ATTR_FSCREATE	0x0004
> +#define LSM_ATTR_KEYCREATE	0x0008
> +#define LSM_ATTR_PREV		0x0010
> +#define LSM_ATTR_SOCKCREATE	0x0020
> +
>   #endif /* _UAPI_LINUX_LSM_H */
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index b859b1af6c75..3a6bf4f95d84 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -1206,6 +1206,7 @@ struct lsm_blob_sizes apparmor_blob_sizes __lsm_ro_after_init = {
>   static struct lsm_id apparmor_lsmid __lsm_ro_after_init = {
>   	.lsm = "apparmor",
>   	.id = LSM_ID_APPARMOR,
> +	.attrs_used = LSM_ATTR_CURRENT | LSM_ATTR_PREV | LSM_ATTR_EXEC,
>   };
>   
>   static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 5fcce36267bd..e831d9c38c54 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -7018,6 +7018,8 @@ static int selinux_uring_cmd(struct io_uring_cmd *ioucmd)
>   static struct lsm_id selinux_lsmid __lsm_ro_after_init = {
>   	.lsm = "selinux",
>   	.id = LSM_ID_SELINUX,
> +	.attrs_used = LSM_ATTR_CURRENT | LSM_ATTR_EXEC | LSM_ATTR_FSCREATE |
> +		      LSM_ATTR_KEYCREATE | LSM_ATTR_PREV | LSM_ATTR_SOCKCREATE,
>   };
>   
>   /*
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index c7ba80e20b8d..c2a05217bde4 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -4791,6 +4791,7 @@ struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init = {
>   static struct lsm_id smack_lsmid __lsm_ro_after_init = {
>   	.lsm = "smack",
>   	.id = LSM_ID_SMACK,
> +	.attrs_used = LSM_ATTR_CURRENT,
>   };
>   
>   static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {