security,lockdown,selinux: implement SELinux lockdown

Implement a SELinux hook for lockdown.  If the lockdown module is also
enabled, then a denial by the lockdown module will take precedence over
SELinux, so SELinux can only further restrict lockdown decisions.
The SELinux hook only distinguishes at the granularity of integrity
versus confidentiality similar to the lockdown module, but includes the
full lockdown reason as part of the audit record as a hint in diagnosing
what triggered the denial.  To support this auditing, move the
lockdown_reasons[] string array from being private to the lockdown
module to the security framework so that it can be used by the lsm audit
code and so that it is always available even when the lockdown module
is disabled.

Note that the SELinux implementation allows the integrity and
confidentiality reasons to be controlled independently from one another.
Thus, in an SELinux policy, one could allow operations that specify
an integrity reason while blocking operations that specify a
confidentiality reason. The SELinux hook implementation is
stricter than the lockdown module in validating the provided reason value.

Sample AVC audit output from denials:
avc:  denied  { integrity } for pid=3402 comm="fwupd"
 lockdown_reason="/dev/mem,kmem,port" scontext=system_u:system_r:fwupd_t:s0
 tcontext=system_u:system_r:fwupd_t:s0 tclass=lockdown permissive=0

avc:  denied  { confidentiality } for pid=4628 comm="cp"
 lockdown_reason="/proc/kcore access"
 scontext=unconfined_u:unconfined_r:test_lockdown_integrity_t:s0-s0:c0.c1023
 tcontext=unconfined_u:unconfined_r:test_lockdown_integrity_t:s0-s0:c0.c1023
 tclass=lockdown permissive=0

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
[PM: some merge fuzz do the the perf hooks]
Signed-off-by: Paul Moore <paul@paul-moore.com>

2 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/lsm_audit.h b/include/linux/lsm_audit.h
index 915330abf6e5..99d629fd9944 100644
--- a/include/linux/lsm_audit.h
+++ b/include/linux/lsm_audit.h
@@ -74,6 +74,7 @@ struct common_audit_data {
 #define LSM_AUDIT_DATA_FILE	12
 #define LSM_AUDIT_DATA_IBPKEY	13
 #define LSM_AUDIT_DATA_IBENDPORT 14
+#define LSM_AUDIT_DATA_LOCKDOWN 15
 	union 	{
 		struct path path;
 		struct dentry *dentry;
@@ -93,6 +94,7 @@ struct common_audit_data {
 		struct file *file;
 		struct lsm_ibpkey_audit *ibpkey;
 		struct lsm_ibendport_audit *ibendport;
+		int reason;
 	} u;
 	/* this union contains LSM specific data */
 	union {
diff --git a/include/linux/security.h b/include/linux/security.h
index 3e8d4bacd59d..64b19f050343 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -128,6 +128,8 @@ enum lockdown_reason {
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
 
+extern const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1];
+
 /* These functions are in security/commoncap.c */
 extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
 		       int cap, unsigned int opts);