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

[Casey Schaufler]

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@xxxxxxxxxxxxxxxx>
---
 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@xxxxxxxxxxxxxxxx>
+.. 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;
 };
 
 /*
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 = {
-- 
2.38.1