SELinux: Improve read/write performance

It reduces the selinux overhead on read/write by only revalidating
permissions in selinux_file_permission if the task or inode labels have
changed or the policy has changed since the open-time check.  A new LSM
hook, security_dentry_open, is added to capture the necessary state at open
time to allow this optimization.

(see http://marc.info/?l=selinux&m=118972995207740&w=2)

Signed-off-by: Yuichi Nakamura<ynakam@hitachisoft.jp>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 52 insertions, 1 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index cf76150..97b7e27 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -14,6 +14,8 @@
  *                          <dgoeddel@trustedcs.com>
  *  Copyright (C) 2006 Hewlett-Packard Development Company, L.P.
  *                     Paul Moore, <paul.moore@hp.com>
+ *  Copyright (C) 2007 Hitachi Software Engineering Co., Ltd.
+ *                     Yuichi Nakamura <ynakam@hitachisoft.jp>
  *
  *	This program is free software; you can redistribute it and/or modify
  *	it under the terms of the GNU General Public License version 2,
@@ -2464,7 +2466,7 @@ static int selinux_inode_listsecurity(struct inode *inode, char *buffer, size_t
 
 /* file security operations */
 
-static int selinux_file_permission(struct file *file, int mask)
+static int selinux_revalidate_file_permission(struct file *file, int mask)
 {
 	int rc;
 	struct inode *inode = file->f_path.dentry->d_inode;
@@ -2486,6 +2488,25 @@ static int selinux_file_permission(struct file *file, int mask)
 	return selinux_netlbl_inode_permission(inode, mask);
 }
 
+static int selinux_file_permission(struct file *file, int mask)
+{
+	struct inode *inode = file->f_path.dentry->d_inode;
+	struct task_security_struct *tsec = current->security;
+	struct file_security_struct *fsec = file->f_security;
+	struct inode_security_struct *isec = inode->i_security;
+
+	if (!mask) {
+		/* No permission to check.  Existence test. */
+		return 0;
+	}
+
+	if (tsec->sid == fsec->sid && fsec->isid == isec->sid
+	    && fsec->pseqno == avc_policy_seqno())
+		return selinux_netlbl_inode_permission(inode, mask);
+
+	return selinux_revalidate_file_permission(file, mask);
+}
+
 static int selinux_file_alloc_security(struct file *file)
 {
 	return file_alloc_security(file);
@@ -2725,6 +2746,34 @@ static int selinux_file_receive(struct file *file)
 	return file_has_perm(current, file, file_to_av(file));
 }
 
+static int selinux_dentry_open(struct file *file)
+{
+	struct file_security_struct *fsec;
+	struct inode *inode;
+	struct inode_security_struct *isec;
+	inode = file->f_path.dentry->d_inode;
+	fsec = file->f_security;
+	isec = inode->i_security;
+	/*
+	 * Save inode label and policy sequence number
+	 * at open-time so that selinux_file_permission
+	 * can determine whether revalidation is necessary.
+	 * Task label is already saved in the file security
+	 * struct as its SID.
+	 */
+	fsec->isid = isec->sid;
+	fsec->pseqno = avc_policy_seqno();
+	/*
+	 * Since the inode label or policy seqno may have changed
+	 * between the selinux_inode_permission check and the saving
+	 * of state above, recheck that access is still permitted.
+	 * Otherwise, access might never be revalidated against the
+	 * new inode label or new policy.
+	 * This check is not redundant - do not remove.
+	 */
+	return inode_has_perm(current, inode, file_to_av(file), NULL);
+}
+
 /* task security operations */
 
 static int selinux_task_create(unsigned long clone_flags)
@@ -4794,6 +4843,8 @@ static struct security_operations selinux_ops = {
 	.file_send_sigiotask =		selinux_file_send_sigiotask,
 	.file_receive =			selinux_file_receive,
 
+	.dentry_open =                  selinux_dentry_open,
+
 	.task_create =			selinux_task_create,
 	.task_alloc_security =		selinux_task_alloc_security,
 	.task_free_security =		selinux_task_free_security,