selinux: treat atomic flags more carefully

The disabled/enforcing/initialized flags are all accessed concurrently
by threads so use the appropriate accessors that ensure atomicity and
document that it is expected.

Use smp_load/acquire...() helpers (with memory barriers) for the
initialized flag, since it gates access to the rest of the state
structures.

Note that the disabled flag is currently not used for anything other
than avoiding double disable, but it will be used for bailing out of
hooks once security_delete_hooks() is removed.
Signed-off-by: NOndrej Mosnacek <omosnace@redhat.com>
Acked-by: NStephen Smalley <sds@tycho.nsa.gov>
Reviewed-by: NKees Cook <keescook@chromium.org>
Reviewed-by: NJames Morris <jamorris@linux.microsoft.com>
Signed-off-by: NPaul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -272,7 +272,7 @@ static int __inode_security_revalidate(struct inode *inode,
 
 	might_sleep_if(may_sleep);
 
-	if (selinux_state.initialized &&
+	if (selinux_initialized(&selinux_state) &&
 	    isec->initialized != LABEL_INITIALIZED) {
 		if (!may_sleep)
 			return -ECHILD;
@@ -659,7 +659,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 
 	mutex_lock(&sbsec->lock);
 
-	if (!selinux_state.initialized) {
+	if (!selinux_initialized(&selinux_state)) {
 		if (!opts) {
 			/* Defer initialization until selinux_complete_init,
 			   after the initial policy is loaded and the security
@@ -929,7 +929,7 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
 	 * if the parent was able to be mounted it clearly had no special lsm
 	 * mount options.  thus we can safely deal with this superblock later
 	 */
-	if (!selinux_state.initialized)
+	if (!selinux_initialized(&selinux_state))
 		return 0;
 
 	/*
@@ -1104,7 +1104,7 @@ static int selinux_sb_show_options(struct seq_file *m, struct super_block *sb)
 	if (!(sbsec->flags & SE_SBINITIALIZED))
 		return 0;
 
-	if (!selinux_state.initialized)
+	if (!selinux_initialized(&selinux_state))
 		return 0;
 
 	if (sbsec->flags & FSCONTEXT_MNT) {
@@ -2921,7 +2921,8 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 		isec->initialized = LABEL_INITIALIZED;
 	}
 
-	if (!selinux_state.initialized || !(sbsec->flags & SBLABEL_MNT))
+	if (!selinux_initialized(&selinux_state) ||
+	    !(sbsec->flags & SBLABEL_MNT))
 		return -EOPNOTSUPP;
 
 	if (name)
@@ -3144,7 +3145,7 @@ static int selinux_inode_setxattr(struct dentry *dentry, const char *name,
 		return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
 	}
 
-	if (!selinux_state.initialized)
+	if (!selinux_initialized(&selinux_state))
 		return (inode_owner_or_capable(inode) ? 0 : -EPERM);
 
 	sbsec = inode->i_sb->s_security;
@@ -3230,7 +3231,7 @@ static void selinux_inode_post_setxattr(struct dentry *dentry, const char *name,
 		return;
 	}
 
-	if (!selinux_state.initialized) {
+	if (!selinux_initialized(&selinux_state)) {
 		/* If we haven't even been initialized, then we can't validate
 		 * against a policy, so leave the label as invalid. It may
 		 * resolve to a valid label on the next revalidation try if
@@ -7300,17 +7301,17 @@ static void selinux_nf_ip_exit(void)
 #ifdef CONFIG_SECURITY_SELINUX_DISABLE
 int selinux_disable(struct selinux_state *state)
 {
-	if (state->initialized) {
+	if (selinux_initialized(state)) {
 		/* Not permitted after initial policy load. */
 		return -EINVAL;
 	}
 
-	if (state->disabled) {
+	if (selinux_disabled(state)) {
 		/* Only do this once. */
 		return -EINVAL;
 	}
 
-	state->disabled = 1;
+	selinux_mark_disabled(state);
 
 	pr_info("SELinux:  Disabled at runtime.\n");
 

security/selinux/include/security.h

@@ -117,15 +117,27 @@ void selinux_avc_init(struct selinux_avc **avc);
 
 extern struct selinux_state selinux_state;
 
+static inline bool selinux_initialized(const struct selinux_state *state)
+{
+	/* do a synchronized load to avoid race conditions */
+	return smp_load_acquire(&state->initialized);
+}
+
+static inline void selinux_mark_initialized(struct selinux_state *state)
+{
+	/* do a synchronized write to avoid race conditions */
+	smp_store_release(&state->initialized, true);
+}
+
 #ifdef CONFIG_SECURITY_SELINUX_DEVELOP
 static inline bool enforcing_enabled(struct selinux_state *state)
 {
-	return state->enforcing;
+	return READ_ONCE(state->enforcing);
 }
 
 static inline void enforcing_set(struct selinux_state *state, bool value)
 {
-	state->enforcing = value;
+	WRITE_ONCE(state->enforcing, value);
 }
 #else
 static inline bool enforcing_enabled(struct selinux_state *state)
@@ -138,6 +150,23 @@ static inline void enforcing_set(struct selinux_state *state, bool value)
 }
 #endif
 
+#ifdef CONFIG_SECURITY_SELINUX_DISABLE
+static inline bool selinux_disabled(struct selinux_state *state)
+{
+	return READ_ONCE(state->disabled);
+}
+
+static inline void selinux_mark_disabled(struct selinux_state *state)
+{
+	WRITE_ONCE(state->disabled, true);
+}
+#else
+static inline bool selinux_disabled(struct selinux_state *state)
+{
+	return false;
+}
+#endif
+
 static inline bool selinux_policycap_netpeer(void)
 {
 	struct selinux_state *state = &selinux_state;

security/selinux/ss/services.c

@@ -767,7 +767,7 @@ static int security_compute_validatetrans(struct selinux_state *state,
 	int rc = 0;
 
 
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		return 0;
 
 	read_lock(&state->ss->policy_rwlock);
@@ -868,7 +868,7 @@ int security_bounded_transition(struct selinux_state *state,
 	int index;
 	int rc;
 
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		return 0;
 
 	read_lock(&state->ss->policy_rwlock);
@@ -1027,7 +1027,7 @@ void security_compute_xperms_decision(struct selinux_state *state,
 	memset(xpermd->dontaudit->p, 0, sizeof(xpermd->dontaudit->p));
 
 	read_lock(&state->ss->policy_rwlock);
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		goto allow;
 
 	policydb = &state->ss->policydb;
@@ -1112,7 +1112,7 @@ void security_compute_av(struct selinux_state *state,
 	read_lock(&state->ss->policy_rwlock);
 	avd_init(state, avd);
 	xperms->len = 0;
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		goto allow;
 
 	policydb = &state->ss->policydb;
@@ -1166,7 +1166,7 @@ void security_compute_av_user(struct selinux_state *state,
 
 	read_lock(&state->ss->policy_rwlock);
 	avd_init(state, avd);
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		goto allow;
 
 	policydb = &state->ss->policydb;
@@ -1286,7 +1286,7 @@ int security_sidtab_hash_stats(struct selinux_state *state, char *page)
 {
 	int rc;
 
-	if (!state->initialized) {
+	if (!selinux_initialized(state)) {
 		pr_err("SELinux: %s:  called before initial load_policy\n",
 		       __func__);
 		return -EINVAL;
@@ -1320,7 +1320,7 @@ static int security_sid_to_context_core(struct selinux_state *state,
 		*scontext = NULL;
 	*scontext_len  = 0;
 
-	if (!state->initialized) {
+	if (!selinux_initialized(state)) {
 		if (sid <= SECINITSID_NUM) {
 			char *scontextp;
 
@@ -1549,7 +1549,7 @@ static int security_context_to_sid_core(struct selinux_state *state,
 	if (!scontext2)
 		return -ENOMEM;
 
-	if (!state->initialized) {
+	if (!selinux_initialized(state)) {
 		int i;
 
 		for (i = 1; i < SECINITSID_NUM; i++) {
@@ -1736,7 +1736,7 @@ static int security_compute_sid(struct selinux_state *state,
 	int rc = 0;
 	bool sock;
 
-	if (!state->initialized) {
+	if (!selinux_initialized(state)) {
 		switch (orig_tclass) {
 		case SECCLASS_PROCESS: /* kernel value */
 			*out_sid = ssid;
@@ -2198,7 +2198,7 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len)
 		goto out;
 	}
 
-	if (!state->initialized) {
+	if (!selinux_initialized(state)) {
 		rc = policydb_read(policydb, fp);
 		if (rc) {
 			kfree(newsidtab);
@@ -2223,7 +2223,7 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len)
 
 		state->ss->sidtab = newsidtab;
 		security_load_policycaps(state);
-		state->initialized = 1;
+		selinux_mark_initialized(state);
 		seqno = ++state->ss->latest_granting;
 		selinux_complete_init();
 		avc_ss_reset(state->avc, seqno);
@@ -2639,7 +2639,7 @@ int security_get_user_sids(struct selinux_state *state,
 	*sids = NULL;
 	*nel = 0;
 
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		goto out;
 
 	read_lock(&state->ss->policy_rwlock);
@@ -2875,7 +2875,7 @@ int security_get_bools(struct selinux_state *state,
 	struct policydb *policydb;
 	int i, rc;
 
-	if (!state->initialized) {
+	if (!selinux_initialized(state)) {
 		*len = 0;
 		*names = NULL;
 		*values = NULL;
@@ -3050,7 +3050,7 @@ int security_sid_mls_copy(struct selinux_state *state,
 	int rc;
 
 	rc = 0;
-	if (!state->initialized || !policydb->mls_enabled) {
+	if (!selinux_initialized(state) || !policydb->mls_enabled) {
 		*new_sid = sid;
 		goto out;
 	}
@@ -3217,7 +3217,7 @@ int security_get_classes(struct selinux_state *state,
 	struct policydb *policydb = &state->ss->policydb;
 	int rc;
 
-	if (!state->initialized) {
+	if (!selinux_initialized(state)) {
 		*nclasses = 0;
 		*classes = NULL;
 		return 0;
@@ -3366,7 +3366,7 @@ int selinux_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
 
 	*rule = NULL;
 
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		return -EOPNOTSUPP;
 
 	switch (field) {
@@ -3665,7 +3665,7 @@ int security_netlbl_secattr_to_sid(struct selinux_state *state,
 	struct context *ctx;
 	struct context ctx_new;
 
-	if (!state->initialized) {
+	if (!selinux_initialized(state)) {
 		*sid = SECSID_NULL;
 		return 0;
 	}
@@ -3732,7 +3732,7 @@ int security_netlbl_sid_to_secattr(struct selinux_state *state,
 	int rc;
 	struct context *ctx;
 
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		return 0;
 
 	read_lock(&state->ss->policy_rwlock);
@@ -3771,7 +3771,7 @@ int security_read_policy(struct selinux_state *state,
 	int rc;
 	struct policy_file fp;
 
-	if (!state->initialized)
+	if (!selinux_initialized(state))
 		return -EINVAL;
 
 	*len = security_policydb_len(state);