selinux: refactor changing booleans

Refactor the logic for changing SELinux policy booleans in a similar
manner to the refactoring of policy load, thereby reducing the
size of the critical section when the policy write-lock is held
and making it easier to convert the policy rwlock to RCU in the
future.  Instead of directly modifying the policydb in place, modify
a copy and then swap it into place through a single pointer update.
Only fully copy the portions of the policydb that are affected by
boolean changes to avoid the full cost of a deep policydb copy.
Introduce another level of indirection for the sidtab since changing
booleans does not require updating the sidtab, unlike policy load.
While we are here, create a common helper for notifying
other kernel components and userspace of a policy change and call it
from both security_set_bools() and selinux_policy_commit().

Based on an old (2004) patch by Kaigai Kohei [1] to convert the policy
rwlock to RCU that was deferred at the time since it did not
significantly improve performance and introduced complexity. Peter
Enderborg later submitted a patch series to convert to RCU [2] that
would have made changing booleans a much more expensive operation
by requiring a full policydb_write();policydb_read(); sequence to
deep copy the entire policydb and also had concerns regarding
atomic allocations.

This change is now simplified by the earlier work to encapsulate
policy state in the selinux_policy struct and to refactor
policy load.  After this change, the last major obstacle to
converting the policy rwlock to RCU is likely the sidtab live
convert support.

[1] https://lore.kernel.org/selinux/6e2f9128-e191-ebb3-0e87-74bfccb0767f@tycho.nsa.gov/
[2] https://lore.kernel.org/selinux/20180530141104.28569-1-peter.enderborg@sony.com/Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/ss/avtab.c

@@ -301,7 +301,6 @@ void avtab_destroy(struct avtab *h)
 
 void avtab_init(struct avtab *h)
 {
-	kvfree(h->htable);
 	h->htable = NULL;
 	h->nel = 0;
 }
@@ -340,6 +339,54 @@ int avtab_alloc(struct avtab *h, u32 nrules)
 	return 0;
 }
 
+int avtab_duplicate(struct avtab *new, struct avtab *orig)
+{
+	int i;
+	struct avtab_node *node, *tmp, *tail;
+
+	memset(new, 0, sizeof(*new));
+
+	new->htable = kvcalloc(orig->nslot, sizeof(void *), GFP_KERNEL);
+	if (!new->htable)
+		return -ENOMEM;
+	new->nslot = orig->nslot;
+	new->mask = orig->mask;
+
+	for (i = 0; i < orig->nslot; i++) {
+		tail = NULL;
+		for (node = orig->htable[i]; node; node = node->next) {
+			tmp = kmem_cache_zalloc(avtab_node_cachep, GFP_KERNEL);
+			if (!tmp)
+				goto error;
+			tmp->key = node->key;
+			if (tmp->key.specified & AVTAB_XPERMS) {
+				tmp->datum.u.xperms =
+					kmem_cache_zalloc(avtab_xperms_cachep,
+							GFP_KERNEL);
+				if (!tmp->datum.u.xperms) {
+					kmem_cache_free(avtab_node_cachep, tmp);
+					goto error;
+				}
+				tmp->datum.u.xperms = node->datum.u.xperms;
+			} else
+				tmp->datum.u.data = node->datum.u.data;
+
+			if (tail)
+				tail->next = tmp;
+			else
+				new->htable[i] = tmp;
+
+			tail = tmp;
+			new->nel++;
+		}
+	}
+
+	return 0;
+error:
+	avtab_destroy(new);
+	return -ENOMEM;
+}
+
 void avtab_hash_eval(struct avtab *h, char *tag)
 {
 	int i, chain_len, slots_used, max_chain_len;

security/selinux/ss/avtab.h

@@ -89,6 +89,7 @@ struct avtab {
 
 void avtab_init(struct avtab *h);
 int avtab_alloc(struct avtab *, u32);
+int avtab_duplicate(struct avtab *new, struct avtab *orig);
 struct avtab_datum *avtab_search(struct avtab *h, struct avtab_key *k);
 void avtab_destroy(struct avtab *h);
 void avtab_hash_eval(struct avtab *h, char *tag);

security/selinux/ss/conditional.c

@@ -600,3 +600,159 @@ void cond_compute_av(struct avtab *ctab, struct avtab_key *key,
 			services_compute_xperms_drivers(xperms, node);
 	}
 }
+
+static int cond_dup_av_list(struct cond_av_list *new,
+			struct cond_av_list *orig,
+			struct avtab *avtab)
+{
+	struct avtab_node *avnode;
+	u32 i;
+
+	memset(new, 0, sizeof(*new));
+
+	new->nodes = kcalloc(orig->len, sizeof(*new->nodes), GFP_KERNEL);
+	if (!new->nodes)
+		return -ENOMEM;
+
+	for (i = 0; i < orig->len; i++) {
+		avnode = avtab_search_node(avtab, &orig->nodes[i]->key);
+		if (WARN_ON(!avnode))
+			return -EINVAL;
+		new->nodes[i] = avnode;
+		new->len++;
+	}
+
+	return 0;
+}
+
+static int duplicate_policydb_cond_list(struct policydb *newp,
+					struct policydb *origp)
+{
+	int rc, i, j;
+
+	rc = avtab_duplicate(&newp->te_cond_avtab, &origp->te_cond_avtab);
+	if (rc)
+		return rc;
+
+	newp->cond_list_len = 0;
+	newp->cond_list = kcalloc(origp->cond_list_len,
+				sizeof(*newp->cond_list),
+				GFP_KERNEL);
+	if (!newp->cond_list)
+		goto error;
+
+	for (i = 0; i < origp->cond_list_len; i++) {
+		struct cond_node *newn = &newp->cond_list[i];
+		struct cond_node *orign = &origp->cond_list[i];
+
+		newp->cond_list_len++;
+
+		newn->cur_state = orign->cur_state;
+		newn->expr.nodes = kcalloc(orign->expr.len,
+					sizeof(*newn->expr.nodes), GFP_KERNEL);
+		if (!newn->expr.nodes)
+			goto error;
+		for (j = 0; j < orign->expr.len; j++)
+			newn->expr.nodes[j] = orign->expr.nodes[j];
+		newn->expr.len = orign->expr.len;
+
+		rc = cond_dup_av_list(&newn->true_list, &orign->true_list,
+				&newp->te_cond_avtab);
+		if (rc)
+			goto error;
+
+		rc = cond_dup_av_list(&newn->false_list, &orign->false_list,
+				&newp->te_cond_avtab);
+		if (rc)
+			goto error;
+	}
+
+	return 0;
+
+error:
+	avtab_destroy(&newp->te_cond_avtab);
+	cond_list_destroy(newp);
+	return -ENOMEM;
+}
+
+static int cond_bools_destroy(void *key, void *datum, void *args)
+{
+	/* key was not copied so no need to free here */
+	kfree(datum);
+	return 0;
+}
+
+static int cond_bools_copy(struct hashtab_node *new, struct hashtab_node *orig, void *args)
+{
+	struct cond_bool_datum *datum;
+
+	datum = kmalloc(sizeof(struct cond_bool_datum), GFP_KERNEL);
+	if (!datum)
+		return -ENOMEM;
+
+	memcpy(datum, orig->datum, sizeof(struct cond_bool_datum));
+
+	new->key = orig->key; /* No need to copy, never modified */
+	new->datum = datum;
+	return 0;
+}
+
+static int cond_bools_index(void *key, void *datum, void *args)
+{
+	struct cond_bool_datum *booldatum, **cond_bool_array;
+
+	booldatum = datum;
+	cond_bool_array = args;
+	cond_bool_array[booldatum->value - 1] = booldatum;
+
+	return 0;
+}
+
+static int duplicate_policydb_bools(struct policydb *newdb,
+				struct policydb *orig)
+{
+	struct cond_bool_datum **cond_bool_array;
+	int rc;
+
+	cond_bool_array = kmalloc_array(orig->p_bools.nprim,
+					sizeof(*orig->bool_val_to_struct),
+					GFP_KERNEL);
+	if (!cond_bool_array)
+		return -ENOMEM;
+
+	rc = hashtab_duplicate(&newdb->p_bools.table, &orig->p_bools.table,
+			cond_bools_copy, cond_bools_destroy, NULL);
+	if (rc) {
+		kfree(cond_bool_array);
+		return -ENOMEM;
+	}
+
+	hashtab_map(&newdb->p_bools.table, cond_bools_index, cond_bool_array);
+	newdb->bool_val_to_struct = cond_bool_array;
+
+	newdb->p_bools.nprim = orig->p_bools.nprim;
+
+	return 0;
+}
+
+void cond_policydb_destroy_dup(struct policydb *p)
+{
+	hashtab_map(&p->p_bools.table, cond_bools_destroy, NULL);
+	hashtab_destroy(&p->p_bools.table);
+	cond_policydb_destroy(p);
+}
+
+int cond_policydb_dup(struct policydb *new, struct policydb *orig)
+{
+	cond_policydb_init(new);
+
+	if (duplicate_policydb_bools(new, orig))
+		return -ENOMEM;
+
+	if (duplicate_policydb_cond_list(new, orig)) {
+		cond_policydb_destroy_dup(new);
+		return -ENOMEM;
+	}
+
+	return 0;
+}

security/selinux/ss/conditional.h

@@ -79,5 +79,7 @@ void cond_compute_av(struct avtab *ctab, struct avtab_key *key,
 void cond_compute_xperms(struct avtab *ctab, struct avtab_key *key,
 		struct extended_perms_decision *xpermd);
 void evaluate_cond_nodes(struct policydb *p);
+void cond_policydb_destroy_dup(struct policydb *p);
+int cond_policydb_dup(struct policydb *new, struct policydb *orig);
 
 #endif /* _CONDITIONAL_H_ */

security/selinux/ss/hashtab.c

@@ -122,6 +122,59 @@ void hashtab_stat(struct hashtab *h, struct hashtab_info *info)
 	info->max_chain_len = max_chain_len;
 }
 
+int hashtab_duplicate(struct hashtab *new, struct hashtab *orig,
+		int (*copy)(struct hashtab_node *new,
+			struct hashtab_node *orig, void *args),
+		int (*destroy)(void *k, void *d, void *args),
+		void *args)
+{
+	struct hashtab_node *cur, *tmp, *tail;
+	int i, rc;
+
+	memset(new, 0, sizeof(*new));
+
+	new->htable = kcalloc(orig->size, sizeof(*new->htable), GFP_KERNEL);
+	if (!new->htable)
+		return -ENOMEM;
+
+	new->size = orig->size;
+
+	for (i = 0; i < orig->size; i++) {
+		tail = NULL;
+		for (cur = orig->htable[i]; cur; cur = cur->next) {
+			tmp = kmem_cache_zalloc(hashtab_node_cachep,
+						GFP_KERNEL);
+			if (!tmp)
+				goto error;
+			rc = copy(tmp, cur, args);
+			if (rc) {
+				kmem_cache_free(hashtab_node_cachep, tmp);
+				goto error;
+			}
+			tmp->next = NULL;
+			if (!tail)
+				new->htable[i] = tmp;
+			else
+				tail->next = tmp;
+			tail = tmp;
+			new->nel++;
+		}
+	}
+
+	return 0;
+
+ error:
+	for (i = 0; i < new->size; i++) {
+		for (cur = new->htable[i]; cur; cur = tmp) {
+			tmp = cur->next;
+			destroy(cur->key, cur->datum, args);
+			kmem_cache_free(hashtab_node_cachep, cur);
+		}
+	}
+	kmem_cache_free(hashtab_node_cachep, new);
+	return -ENOMEM;
+}
+
 void __init hashtab_cache_init(void)
 {
 		hashtab_node_cachep = kmem_cache_create("hashtab_node",

security/selinux/ss/hashtab.h

@@ -136,6 +136,12 @@ int hashtab_map(struct hashtab *h,
 		int (*apply)(void *k, void *d, void *args),
 		void *args);
 
+int hashtab_duplicate(struct hashtab *new, struct hashtab *orig,
+		int (*copy)(struct hashtab_node *new,
+			struct hashtab_node *orig, void *args),
+		int (*destroy)(void *k, void *d, void *args),
+		void *args);
+
 /* Fill info with some hash table statistics */
 void hashtab_stat(struct hashtab *h, struct hashtab_info *info);
 

security/selinux/ss/services.h

@@ -23,7 +23,7 @@ struct selinux_map {
 };
 
 struct selinux_policy {
-	struct sidtab sidtab;
+	struct sidtab *sidtab;
 	struct policydb policydb;
 	struct selinux_map map;
 };