lsm: add the lsm_prop data structure

When more than one security module is exporting data to audit and
networking sub-systems a single 32 bit integer is no longer
sufficient to represent the data. Add a structure to be used instead.

The lsm_prop structure definition is intended to keep the LSM
specific information private to the individual security modules.
The module specific information is included in a new set of
header files under include/lsm. Each security module is allowed
to define the information included for its use in the lsm_prop.
SELinux includes a u32 secid. Smack includes a pointer into its
global label list. The conditional compilation based on feature
inclusion is contained in the include/lsm files.

Cc: apparmor@lists.ubuntu.com
Cc: bpf@vger.kernel.org
Cc: selinux@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Suggested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: John Johansen <john.johansen@canonical.com>
[PM: added include/linux/lsm/ to MAINTAINERS, subj tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: cschaufler

MAINTAINERS

@@ -20846,6 +20846,7 @@ Q:	https://patchwork.kernel.org/project/linux-security-module/list
 B:	mailto:linux-security-module@vger.kernel.org
 P:	https://github.com/LinuxSecurityModule/kernel/blob/main/README.md
 T:	git https://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/lsm.git
+F:	include/linux/lsm/
 F:	include/linux/lsm_audit.h
 F:	include/linux/lsm_hook_defs.h
 F:	include/linux/lsm_hooks.h

include/linux/lsm/apparmor.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Linux Security Module interface to other subsystems.
+ * AppArmor presents single pointer to an aa_label structure.
+ */
+#ifndef __LINUX_LSM_APPARMOR_H
+#define __LINUX_LSM_APPARMOR_H
+
+struct aa_label;
+
+struct lsm_prop_apparmor {
+#ifdef CONFIG_SECURITY_APPARMOR
+	struct aa_label *label;
+#endif
+};
+
+#endif /* ! __LINUX_LSM_APPARMOR_H */

include/linux/lsm/bpf.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Linux Security Module interface to other subsystems.
+ * BPF may present a single u32 value.
+ */
+#ifndef __LINUX_LSM_BPF_H
+#define __LINUX_LSM_BPF_H
+#include <linux/types.h>
+
+struct lsm_prop_bpf {
+#ifdef CONFIG_BPF_LSM
+	u32 secid;
+#endif
+};
+
+#endif /* ! __LINUX_LSM_BPF_H */

include/linux/lsm/selinux.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Linux Security Module interface to other subsystems.
+ * SELinux presents a single u32 value which is known as a secid.
+ */
+#ifndef __LINUX_LSM_SELINUX_H
+#define __LINUX_LSM_SELINUX_H
+#include <linux/types.h>
+
+struct lsm_prop_selinux {
+#ifdef CONFIG_SECURITY_SELINUX
+	u32 secid;
+#endif
+};
+
+#endif /* ! __LINUX_LSM_SELINUX_H */

include/linux/lsm/smack.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Linux Security Module interface to other subsystems.
+ * Smack presents a pointer into the global Smack label list.
+ */
+#ifndef __LINUX_LSM_SMACK_H
+#define __LINUX_LSM_SMACK_H
+
+struct smack_known;
+
+struct lsm_prop_smack {
+#ifdef CONFIG_SECURITY_SMACK
+	struct smack_known *skp;
+#endif
+};
+
+#endif /* ! __LINUX_LSM_SMACK_H */

include/linux/security.h

@@ -34,6 +34,10 @@
 #include <linux/sockptr.h>
 #include <linux/bpf.h>
 #include <uapi/linux/lsm.h>
+#include <linux/lsm/selinux.h>
+#include <linux/lsm/smack.h>
+#include <linux/lsm/apparmor.h>
+#include <linux/lsm/bpf.h>
 
 struct linux_binprm;
 struct cred;
@@ -152,6 +156,22 @@ enum lockdown_reason {
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
 
+/* scaffolding */
+struct lsm_prop_scaffold {
+	u32 secid;
+};
+
+/*
+ * Data exported by the security modules
+ */
+struct lsm_prop {
+	struct lsm_prop_selinux selinux;
+	struct lsm_prop_smack smack;
+	struct lsm_prop_apparmor apparmor;
+	struct lsm_prop_bpf bpf;
+	struct lsm_prop_scaffold scaffold;
+};
+
 extern const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1];
 extern u32 lsm_active_cnt;
 extern const struct lsm_id *lsm_idlist[];