[PATCH v2 1/3] selinux: simplify away security_policydb_len()

[Ondrej Mosnacek <omosnace@xxxxxxxxxx>]

Remove the security_policydb_len() calls from sel_open_policy() and
instead update the inode size from the size returned from
security_read_policy().

Since after this change security_policydb_len() is only called from
security_load_policy(), remove it entirely and just open-code it there.

Also, since security_load_policy() is always called with fsi->mutex
held, make it dereference the policy pointer directly and drop the
unnecessary RCU locking.

Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
---
 security/selinux/include/security.h |  1 -
 security/selinux/selinuxfs.c        | 12 +++++------
 security/selinux/ss/services.c      | 32 ++++++++---------------------
 3 files changed, 15 insertions(+), 30 deletions(-)

diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index 505e51264d51c..839774929a10d 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -218,7 +218,6 @@ void selinux_policy_cancel(struct selinux_state *state,
 			struct selinux_policy *policy);
 int security_read_policy(struct selinux_state *state,
 			 void **data, size_t *len);
-size_t security_policydb_len(struct selinux_state *state);
 
 int security_policycap_supported(struct selinux_state *state,
 				 unsigned int req_cap);
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index d1872adf0c474..fc44c4b8c0692 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -417,16 +417,16 @@ static int sel_open_policy(struct inode *inode, struct file *filp)
 	if (!plm)
 		goto err;
 
-	if (i_size_read(inode) != security_policydb_len(state)) {
-		inode_lock(inode);
-		i_size_write(inode, security_policydb_len(state));
-		inode_unlock(inode);
-	}
-
 	rc = security_read_policy(state, &plm->data, &plm->len);
 	if (rc)
 		goto err;
 
+	if ((size_t)i_size_read(inode) != plm->len) {
+		inode_lock(inode);
+		i_size_write(inode, plm->len);
+		inode_unlock(inode);
+	}
+
 	fsi->policy_opened = 1;
 
 	filp->private_data = plm;
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 8381614627569..7cc2f7486c18f 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2331,22 +2331,6 @@ err:
 	return rc;
 }
 
-size_t security_policydb_len(struct selinux_state *state)
-{
-	struct selinux_policy *policy;
-	size_t len;
-
-	if (!selinux_initialized(state))
-		return 0;
-
-	rcu_read_lock();
-	policy = rcu_dereference(state->policy);
-	len = policy->policydb.len;
-	rcu_read_unlock();
-
-	return len;
-}
-
 /**
  * security_port_sid - Obtain the SID for a port.
  * @protocol: protocol number
@@ -3912,11 +3896,17 @@ int security_read_policy(struct selinux_state *state,
 	int rc;
 	struct policy_file fp;
 
-	if (!selinux_initialized(state))
+	/*
+	 * NOTE: We do not need to take the rcu read lock
+	 * around the code below because other policy-modifying
+	 * operations are already excluded by selinuxfs via
+	 * fsi->mutex.
+	 */
+	policy = rcu_dereference_check(state->policy, 1);
+	if (!policy)
 		return -EINVAL;
 
-	*len = security_policydb_len(state);
-
+	*len = policy->policydb.len;
 	*data = vmalloc_user(*len);
 	if (!*data)
 		return -ENOMEM;
@@ -3924,11 +3914,7 @@ int security_read_policy(struct selinux_state *state,
 	fp.data = *data;
 	fp.len = *len;
 
-	rcu_read_lock();
-	policy = rcu_dereference(state->policy);
 	rc = policydb_write(&policy->policydb, &fp);
-	rcu_read_unlock();
-
 	if (rc)
 		return rc;
 
-- 
2.26.2