[PATCH 3/6] SELinux: Improve read/write performance

James Morris
2007-10-09T23:22:01Z

From: Yuichi Nakamura <ynakam@hitachisoft.jp>

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@localhost.localdomain>
---
fs/open.c | 4 +++
include/linux/security.h | 18 ++++++++++++
security/dummy.c | 6 ++++
security/selinux/avc.c | 5 +++
security/selinux/hooks.c | 53 ++++++++++++++++++++++++++++++++++++-
security/selinux/include/avc.h | 2 +
security/selinux/include/objsec.h | 2 +
7 files changed, 89 insertions(+), 1 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 1d9e5e9..044bfa8 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -757,6 +757,10 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
f->f_op = fops_get(inode->i_fop);
file_move(f, &inode->i_sb->s_files);

+ error = security_dentry_open(f);
+ if (error)
+ goto cleanup_all;
+
if (!open && f->f_op)
open = f->f_op->open;
if (open) {
diff --git a/include/linux/security.h b/include/linux/security.h
index 1a15526..928d479 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -504,6 +504,13 @@ struct request_sock;
* @file contains the file structure being received.
* Return 0 if permission is granted.
*
+ * Security hook for dentry
+ *
+ * @dentry_open
+ * Save open-time permission checking state for later use upon
+ * file_permission, and recheck access if anything has changed
+ * since inode_permission.
+ *
* Security hooks for task operations.
*
* @task_create:
@@ -1256,6 +1263,7 @@ struct security_operations {
int (*file_send_sigiotask) (struct task_struct * tsk,
struct fown_struct * fown, int sig);
int (*file_receive) (struct file * file);
+ int (*dentry_open) (struct file *file);

int (*task_create) (unsigned long clone_flags);
int (*task_alloc_security) (struct task_struct * p);
@@ -1864,6 +1872,11 @@ static inline int security_file_receive (struct file *file)
return security_ops->file_receive (file);
}

+static inline int security_dentry_open (struct file *file)
+{
+ return security_ops->dentry_open (file);
+}
+
static inline int security_task_create (unsigned long clone_flags)
{
return security_ops->task_create (clone_flags);
@@ -2546,6 +2559,11 @@ static inline int security_file_receive (struct file *file)
return 0;
}

+static inline int security_dentry_open (struct file *file)
+{
+ return 0;
+}
+
static inline int security_task_create (unsigned long clone_flags)
{
return 0;
diff --git a/security/dummy.c b/security/dummy.c
index 853ec22..64b647a 100644
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -463,6 +463,11 @@ static int dummy_file_receive (struct file *file)
return 0;
}

+static int dummy_dentry_open (struct file *file)
+{
+ return 0;
+}
+
static int dummy_task_create (unsigned long clone_flags)
{
return 0;
@@ -1033,6 +1038,7 @@ void security_fixup_ops (struct security_operations *ops)
set_to_dummy_if_null(ops, file_set_fowner);
set_to_dummy_if_null(ops, file_send_sigiotask);
set_to_dummy_if_null(ops, file_receive);
+ set_to_dummy_if_null(ops, dentry_open);
set_to_dummy_if_null(ops, task_create);
set_to_dummy_if_null(ops, task_alloc_security);
set_to_dummy_if_null(ops, task_free_security);
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 0e69adf..81b3dff 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 0753b20..e842308 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)
@@ -4790,6 +4839,8 @@ 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 e145f6e..553607a 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 91b88f0..642a9fd 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 {
--
1.5.2.4