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>

4 files changed, 61 insertions, 1 deletions

diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 0e69adf63bdb..81b3dff3cbf0 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -916,3 +916,8 @@ int avc_has_perm(u32 ssid, u32 tsid, u16 tclass,
         avc_audit(ssid, tsid, tclass, requested, &avd, rc, auditdata);
         return rc;
 }
+
+u32 avc_policy_seqno(void)
+{
+        return avc_cache.latest_notif;
+}
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index cf76150e623e..97b7e2738097 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,
diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index e145f6e13b0b..553607a19e92 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -112,6 +112,8 @@ int avc_has_perm(u32 ssid, u32 tsid,
                  u16 tclass, u32 requested,
                  struct avc_audit_data *auditdata);
 
+u32 avc_policy_seqno(void);
+
 #define AVC_CALLBACK_GRANT              1
 #define AVC_CALLBACK_TRY_REVOKE         2
 #define AVC_CALLBACK_REVOKE             4
diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
index 91b88f0ba20c..642a9fd319ad 100644
--- a/security/selinux/include/objsec.h
+++ b/security/selinux/include/objsec.h
@@ -53,6 +53,8 @@ struct file_security_struct {
         struct file *file;              /* back pointer to file object */
         u32 sid;              /* SID of open file description */
         u32 fown_sid;         /* SID of file owner (for SIGIO) */
+        u32 isid;             /* SID of inode at the time of file open */
+        u32 pseqno;           /* Policy seqno at the time of file open */
 };
 
 struct superblock_security_struct {