selinux: Improving SELinux read/write performance

Hello.

As I posted before in selinux list,
I found big overhead of SELinux in read/write on some CPUs, and trying tuning.
There were discussion in previous threads.
Part 1:
http://marc.info/?t=118845343400001&r=1&w=2
Part 2:
http://marc.info/?t=118880749800004&r=1&w=2

I would like to RFC again about this topic.

1. Background
Look at benchmark result below.
lmbench simple read/write.
Big overhead exists especially on SH(SuperH) arch.

1) Result for x86(Pentium 4 2.6Ghz), kernel 2.6.22

                Base  SELinux  Overhead(%)
Simple read     1.10  1.24     12.3
Simple write    1.00  1.14     14.0

* Base: kernel compiled without SELinux support

2) Result for SH(SH4, SH7751R), kernel 2.6.22

                Base    SELinux   Overhead(%)
Simple read     2.39    5.49      130.5
Simple write    2.07    5.10      146.6
# This result is a little different from previous threads, 
# because I changed some kernel configs.

Overhead more than 100%
I also found about 70-90% overhead in ARM.

2. About patch
I found a overhead in selinux_file_permission function. This is a function that is called in read/write calls, and does SELinux permission check.
SELinux checks permission both in open and read/write time. Stephen Smalley sugessted that we can usually skip permission check in selinux_file_permission.
By this patch,
permission check in selinux_file_permssion is done only when
- sid of task has changed after file open
- sid of inode has changed after file open
- policy load or boolean change happen after file open

To detect these changes,
I added entries in file_security struct and saving these values at file open.

And to save sid of inode at the time of file open, I had to add new LSM hook in __dentry_open function.

3. Benchmark after applying this patch
1) Result for x86(Pentium 4 2.6Ghz), kernel 2.6.22

                Base  SELinux  Overhead(%)
Simple read     1.10  1.12     1.6(Before 12.3)
Simple write    1.00  1.03     3.6(Before 14.0)

2) Result for SH(SH4, SH7751R), kernel 2.6.22

                Base    SELinux   Overhead(%)
Simple read     2.39    2.65      11.1(Before 130.5)
Simple write    2.07    2.28      10.5(Before 146.6)

Performance has improved a lot.
I want comments from community.

Signed-off-by Yuichi Nakamura<[email protected]>

---
 fs/open.c                         |    5 +++
 include/linux/security.h          |   11 +++++++
 security/selinux/avc.c            |    5 ++-
 security/selinux/hooks.c          |   54 +++++++++++++++++++++++++++++++++++++-
 security/selinux/include/objsec.h |    3 ++
 5 files changed, 76 insertions(+), 2 deletions(-)

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/avc.c linux-2.6.22/security/selinux/avc.c

security/selinux/avc.c +1 -0

@@ -123,6 +123,7 @@ DEFINE_PER_CPU(struct avc_cache_stats, a
 #endif
 
 static struct avc_cache avc_cache;
+u32 policy_seqno = 0;
 static struct avc_callback_node *avc_callbacks;
 static struct kmem_cache *avc_node_cachep;
 

security/selinux/hooks.c +18 -0

 {
 	int rc;
 	struct inode *inode = file->f_path.dentry->d_inode;

@@ -2480,6 +2483,43 @@ static int selinux_file_permission(struc
 	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->tsid) {
+		if (tsec->sid != fsec->sid) {
+			struct vfsmount *mnt = file->f_path.mnt;
+			struct dentry *dentry = file->f_path.dentry;
+			struct avc_audit_data ad;
+			int rc;

security/selinux/hooks.c +0 -0

 static int selinux_file_alloc_security(struct file *file)
 {
 	return file_alloc_security(file);

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/include/linux/security.h linux-2.6.22/include/linux/security.h

include/linux/security.h +6 -0

@@ -503,6 +503,11 @@ struct request_sock;
  *	@file contains the file structure being received.
  *	Return 0 if permission is granted.
  *
+ * Security hook for dentry
+ *
+ * @dentry_open
+ *   Check permission or get additional information before opening dentry.
+ *
  * Security hooks for task operations.
  *
  * @task_create:

@@ -1253,6 +1258,7 @@ 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 flags);
 
 	int (*task_create) (unsigned long clone_flags);
 	int (*task_alloc_security) (struct task_struct * p);

@@ -1854,6 +1860,11 @@ static inline int security_file_receive 
 	return security_ops->file_receive (file);

Review static int avc_latest_notif_update(int s · line 438

Quoted 10 lines

(quoted diff) +3 -1

@@ -431,8 +432,10 @@ static int avc_latest_notif_update(int s
 			ret = -EAGAIN;
 		}
 	} else {
-		if (seqno > avc_cache.latest_notif)
+		if (seqno > avc_cache.latest_notif) {
 			avc_cache.latest_notif = seqno;
+			policy_seqno = seqno;
+		}

I would have just provided an avc interface for obtaining the seqno, e.g.
u32 avc_policy_seqno(void)

{
	return avc_cache.latest_notif;
}

Quoted 4 lines

(quoted diff) +0 -0

 	}
 	spin_unlock_irqrestore(&notif_lock, flag);
 

security/selinux/hooks.c line 87

Quoted 8 lines

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/hooks.c linux-2.6.22/security/selinux/hooks.c

security/selinux/hooks.c +1 -0

@@ -84,6 +84,7 @@
 extern unsigned int policydb_loaded_version;
 extern int selinux_nlmsg_lookup(u16 sclass, u16 nlmsg_type, u32 *perm);
 extern int selinux_compat_net;
+extern u32 policy_seqno;

I think that they frown upon extern declarations in .c files (versus in .h files), so we don't want to add more - we ultimately should clean up what we presently have.

Quoted 6 lines

security/selinux/hooks.c +0 -0

 #ifdef CONFIG_SECURITY_SELINUX_DEVELOP
 int selinux_enforcing = 0;

@@ -220,6 +221,8 @@ static int file_alloc_security(struct fi
 

security/selinux/hooks.c static int file_alloc_security(struct fi · line 224

Quoted 3 lines

security/selinux/hooks.c +1 -0

 	fsec->file = file;
 	fsec->sid = tsec->sid;
+	fsec->tsid = tsec->sid;

I'm not sure why we need the separate field here, as fsec->sid already holds the allocating task SID and doesn't change.

security/selinux/hooks.c static int file_alloc_security(struct fi · line 225

Quoted 1 line

security/selinux/hooks.c +1 -0

+	fsec->pseqno = policy_seqno;

Not sure that you want to set the seqno here versus from your new hook, as it could conceivably change in between.

Quoted 7 lines

security/selinux/hooks.c +0 -0

 	fsec->fown_sid = tsec->sid;
 	file->f_security = fsec;
 

@@ -2458,7 +2461,7 @@ static int selinux_inode_listsecurity(st
 
 /* file security operations */
 

security/selinux/hooks.c static int selinux_inode_listsecurity(st · line 2464

Quoted 2 lines

security/selinux/hooks.c +1 -1

-static int selinux_file_permission(struct file *file, int mask)
+static int do_selinux_file_permission(struct file *file, int mask)

Might want to rename for clarity, e.g.
selinux_revalidate_file_permission or
selinux_file_permission_slow (slow path) or
something similar.

Quoted 26 lines

security/selinux/hooks.c +18 -0

 {
 	int rc;
 	struct inode *inode = file->f_path.dentry->d_inode;

@@ -2480,6 +2483,43 @@ static int selinux_file_permission(struc
 	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->tsid) {
+		if (tsec->sid != fsec->sid) {
+			struct vfsmount *mnt = file->f_path.mnt;
+			struct dentry *dentry = file->f_path.dentry;
+			struct avc_audit_data ad;
+			int rc;

security/selinux/hooks.c static int selinux_file_permission(struc · line 2513

Quoted 10 lines

security/selinux/hooks.c +10 -0

+			AVC_AUDIT_DATA_INIT(&ad, FS);
+			ad.u.fs.mnt = mnt;
+			ad.u.fs.dentry = dentry;
+			rc = avc_has_perm(tsec->sid, fsec->sid,
+					  SECCLASS_FD,
+					  FD__USE,
+					  &ad);
+			if (rc)
+				return rc;
+		}

Why inline the FD_USE check here given that you are falling back to the full function call anyway? I also don't see why you separate this from the rest of the comparison - I'd just make it something like:

	if (tsec->sid == fsec->sid && isec->sid == fsec->isid &&
	    avc_seqno() == fsec->seqno)
		return selinux_netlbl_inode_permission(inode, mask);
	return selinux_revalidate_file_permission(file, mask);

Quoted 7 lines

security/selinux/hooks.c +0 -0

 static int selinux_file_alloc_security(struct file *file)
 {
 	return file_alloc_security(file);

@@ -2715,6 +2755,16 @@ static int selinux_file_receive(struct f
 	return file_has_perm(current, file, file_to_av(file));
 }
 

security/selinux/hooks.c static int selinux_file_receive(struct f · line 2764

Quoted 7 lines

security/selinux/hooks.c +7 -0

+static int selinux_dentry_open(struct file *file, int flags)
+{
+	struct file_security_struct *fsec;
+	struct inode_security_struct *isec;
+	fsec = file->f_security;
+	isec = file->f_path.dentry->d_inode->i_security;
+	fsec->isid = isec->sid;

Set the seqno here too. Ideally, it would come straight from the AVC entry that was used for the open-time check, but that is a bit more invasive and there will always be a small window there.

Quoted 4 lines

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/include/objsec.h linux-2.6.22/security/selinux/include/objsec.h

security/selinux/include/objsec.h +0 -0

@@ -53,6 +53,9 @@ struct file_security_struct {

security/selinux/include/objsec.h struct file_security_struct { · line 58

Quoted 6 lines

security/selinux/include/objsec.h +3 -0

 	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 tsid;             /* SID of task at the time of file open*/
+	u32 isid;             /* SID of inode at the time of file open */
+	u32 pseqno;           /* Policy seqno at the time of file open */

No need for tsid above I think.

Quoted 27 lines

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/include/linux/security.h linux-2.6.22/include/linux/security.h

include/linux/security.h +6 -0

@@ -503,6 +503,11 @@ struct request_sock;
  *	@file contains the file structure being received.
  *	Return 0 if permission is granted.
  *
+ * Security hook for dentry
+ *
+ * @dentry_open
+ *   Check permission or get additional information before opening dentry.
+ *
  * Security hooks for task operations.
  *
  * @task_create:

@@ -1253,6 +1258,7 @@ 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 flags);
 
 	int (*task_create) (unsigned long clone_flags);
 	int (*task_alloc_security) (struct task_struct * p);

@@ -1854,6 +1860,11 @@ static inline int security_file_receive 
 	return security_ops->file_receive (file);
 }
 

include/linux/security.h static inline int security_file_receive · line 1870

Quoted 8 lines

include/linux/security.h +5 -0

+static inline int security_dentry_open (struct file *file, int flags)
+{
+	return security_ops->dentry_open (file, flags);
+}
+
 static inline int security_task_create (unsigned long clone_flags)
 {
 	return security_ops->task_create (clone_flags);

Need to also provide the stub definition in the #else case (SECURITY=n) and a stub function for the dummy security module.

Thanks.

Signature · 2 lines

Stephen Smalley
National Security Agency

Next is updated patch.

Signed-off-by Yuichi Nakamura<[email protected]>

---
 fs/open.c                         |    5 +++++
 include/linux/security.h          |   16 ++++++++++++++++
 security/selinux/avc.c            |    5 +++++
 security/selinux/hooks.c          |   36 +++++++++++++++++++++++++++++++++++-
 security/selinux/include/avc.h    |    2 ++
 security/selinux/include/objsec.h |    2 ++
 6 files changed, 65 insertions(+), 1 deletion(-)

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/avc.c linux-2.6.22/security/selinux/avc.c

security/selinux/avc.c +5 -0

@@ -913,3 +913,8 @@ int avc_has_perm(u32 ssid, u32 tsid, u16
 	avc_audit(ssid, tsid, tclass, requested, &avd, rc, auditdata);
 	return rc;
 }
+
+u32 avc_policy_seqno(void)
+{
+	return avc_cache.latest_notif;
+}

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/hooks.c linux-2.6.22/security/selinux/hooks.c

security/selinux/hooks.c +35 -1

@@ -14,6 +14,8 @@
  *                          <[email protected]>
  *  Copyright (C) 2006 Hewlett-Packard Development Company, L.P.
  *                     Paul Moore, <[email protected]>
+ *  Copyright (C) 2007 Hitachi Software Engineering Co., Ltd.
+ *                     Yuichi Nakamura <[email protected]>
  *
  *	This program is free software; you can redistribute it and/or modify
  *	it under the terms of the GNU General Public License version 2,

@@ -2458,7 +2460,7 @@ static int selinux_inode_listsecurity(st
 
 /* 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;

@@ -2480,6 +2482,25 @@ static int selinux_file_permission(struc
 	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);

@@ -2715,6 +2736,17 @@ static int selinux_file_receive(struct f
 	return file_has_perm(current, file, file_to_av(file));
 }
 
+static int selinux_dentry_open(struct file *file, int flags)
+{
+	struct file_security_struct *fsec;
+	struct inode_security_struct *isec;
+	fsec = file->f_security;
+	isec = file->f_path.dentry->d_inode->i_security;
+	fsec->isid = isec->sid;
+	fsec->pseqno = avc_policy_seqno();
+	return 0;
+}
+
 /* task security operations */
 
 static int selinux_task_create(unsigned long clone_flags)

@@ -4780,6 +4812,8 @@ static struct security_operations selinu
 	.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 -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/include/avc.h linux-2.6.22/security/selinux/include/avc.h

security/selinux/include/avc.h +2 -0

@@ -110,6 +110,8 @@ 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 -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/include/objsec.h linux-2.6.22/security/selinux/include/objsec.h

security/selinux/include/objsec.h +2 -0

@@ -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 {

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/fs/open.c linux-2.6.22/fs/open.c

fs/open.c +5 -0

@@ -698,6 +698,11 @@ static struct file *__dentry_open(struct
 
 	if (!open && f->f_op)
 		open = f->f_op->open;
+
+	error = security_dentry_open(f, flags);
+	if (error)
+		goto cleanup_all;
+
 	if (open) {
 		error = open(inode, f);
 		if (error)

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/include/linux/security.h linux-2.6.22/include/linux/security.h

include/linux/security.h +16 -0

@@ -503,6 +503,11 @@ struct request_sock;
  *	@file contains the file structure being received.
  *	Return 0 if permission is granted.
  *
+ * Security hook for dentry
+ *
+ * @dentry_open
+ *   Check permission or get additional information before opening dentry.
+ *
  * Security hooks for task operations.
  *
  * @task_create:

@@ -1253,6 +1258,7 @@ 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 flags);
 
 	int (*task_create) (unsigned long clone_flags);
 	int (*task_alloc_security) (struct task_struct * p);

@@ -1854,6 +1860,11 @@ static inline int security_file_receive 
 	return security_ops->file_receive (file);
 }
 
+static inline int security_dentry_open (struct file *file, int flags)
+{
+	return security_ops->dentry_open (file, flags);
+}
+
 static inline int security_task_create (unsigned long clone_flags)
 {
 	return security_ops->task_create (clone_flags);

@@ -2529,6 +2540,11 @@ static inline int security_file_receive 
 	return 0;
 }
 
+static inline int security_dentry_open (struct file *file, int flags)
+{
+	return 0;
+}
+
 static inline int security_task_create (unsigned long clone_flags)
 {
 	return 0;

Regards,

One other observation about the patch: it presently leaves open a (small) race window in which the file could get relabeled or policy gets reloaded between the time of the normal permission check (from selinux_inode_permission) and the time you copy the inode SID and policy seqno to the file security struct. In which case you might end up never revalidating access upon read/write even though conditions changed since the open-time permission check. Not sure how to cleanly fix in a lock-free manner, and adding locks here will only make matters worse.

Hi.

Stephen Smalley pointed out possibility of race condition in off-list discussion.

Quoted 8 lines · Stephen Smalley

One other observation about the patch: it presently leaves open a (small) race window in which the file could get relabeled or policy gets reloaded between the time of the normal permission check (from selinux_inode_permission) and the time you copy the inode SID and policy seqno to the file security struct. In which case you might end up never revalidating access upon read/write even though conditions changed since the open-time permission check. Not sure how to cleanly fix in a lock-free manner, and adding locks here will only make matters worse.

To fix that, permission has to be checked in selinux_dentry_open. Therefore, in open, number of permission checks increased. As shown in benchmark result below, it does not affect open/close performance so much.

Following is benchmark result.
* Benchmark
lmbench simple read,write,open/close.

* Before tuning
1) Result for x86(Pentium 4 2.6Ghz), kernel 2.6.22

                Base  SELinux  Overhead(%)
Simple read     1.10  1.24     12.3
Simple write    1.02  1.14     14.0
open/close      5.97  7.45     24.9

* Base: kernel compiled without SELinux support

2) Result for SH(SH4, SH7751R), kernel 2.6.22

                Base    SELinux   Overhead(%)
Simple read     2.39    5.49      130.5
Simple write    2.07    5.10      146.6
open/close      32.6    62.8      93.0

* After tuning
1) Result for x86(Pentium 4 2.6Ghz), kernel 2.6.22

                Base  SELinux  Overhead(%)
Simple read     1.10  1.13     2.3(Before 12.3)
Simple write    1.02  1.024    0.6(Before 14.0)
open/close      5.97  7.48     25.3(Before 24.9)

* Base: kernel compiled without SELinux support

2) Result for SH(SH4, SH7751R), kernel 2.6.22

                Base    SELinux   Overhead(%)
Simple read     2.39    2.63      10.4(Before 130.5)
Simple write    2.07    2.34      13.1(Before 146.6)
open/close      32.6    58.7      80.2(before 93.0)

Next is a patch.

* Description of patch
This patch improves performance of read/write in SELinux. It improves performance by skipping permission check in selinux_file_permission. Permission is only checked when sid change or policy load is detected after file open. To detect sid change, new LSM hook securiy_dentry_open is added.

Signed-off-by Yuichi Nakamura<[email protected]>

---
 fs/open.c                         |    5 ++++
 include/linux/security.h          |   16 ++++++++++++++
 security/dummy.c                  |    6 +++++
 security/selinux/avc.c            |    5 ++++
 security/selinux/hooks.c          |   43 +++++++++++++++++++++++++++++++++++++-
 security/selinux/include/avc.h    |    2 +
 security/selinux/include/objsec.h |    2 +
 7 files changed, 78 insertions(+), 1 deletion(-)

security/selinux/hooks.c +3 -0

+	return inode_has_perm(current, inode, file_to_av(file), NULL);
+}
+
 /* task security operations */
 
 static int selinux_task_create(unsigned long clone_flags)

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/fs/open.c linux-2.6.22/fs/open.c

fs/open.c +0 -0

 	if (open) {
 		error = open(inode, f);
 		if (error)

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/include/linux/security.h linux-2.6.22/include/linux/security.h

On Wed, 2007-09-12 at 17:51 +0900, Yuichi Nakamura wrote:

Thanks, a few comments below.

Quoted 7 lines

* Description of patch
This patch improves performance of read/write in SELinux. It improves performance by skipping permission check in selinux_file_permission. Permission is only checked when sid change or policy load is detected after file open. To detect sid change, new LSM hook securiy_dentry_open is added.

I think I'd reword this a little, e.g.

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.

Quoted 11 lines

Signed-off-by Yuichi Nakamura<[email protected]>

---
 fs/open.c                         |    5 ++++
 include/linux/security.h          |   16 ++++++++++++++
 security/dummy.c                  |    6 +++++
 security/selinux/avc.c            |    5 ++++
 security/selinux/hooks.c          |   43 +++++++++++++++++++++++++++++++++++++-
 security/selinux/include/avc.h    |    2 +
 security/selinux/include/objsec.h |    2 +
 7 files changed, 78 insertions(+), 1 deletion(-)

<snip>

Quoted 5 lines

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/hooks.c linux-2.6.22/security/selinux/hooks.c

security/selinux/hooks.c +0 -0

@@ -80,6 +82,7 @@
 

security/selinux/hooks.c line 85

Quoted 3 lines

security/selinux/hooks.c +1 -0

 #define XATTR_SELINUX_SUFFIX "selinux"
 #define XATTR_NAME_SELINUX XATTR_SECURITY_PREFIX XATTR_SELINUX_SUFFIX
+#define ACC_MODE(x) ("\000\004\002\006"[(x)&O_ACCMODE])

Leftover from prior version of the patch, no longer needed.

<snip>

security/selinux/hooks.c static int selinux_file_receive(struct f · line 2747

Quoted 12 lines

security/selinux/hooks.c +8 -0

@@ -2715,6 +2737,23 @@ static int selinux_file_receive(struct f
 	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;

I'd add a comment here, e.g.
/*
* 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.
*/

security/selinux/hooks.c static int selinux_file_receive(struct f · line 2753

Quoted 7 lines

security/selinux/hooks.c +6 -0

+	fsec->isid = isec->sid;
+	fsec->pseqno = avc_policy_seqno();
+
+	/*Permission has to be rechecked here.
+	  Policy load of inode sid can happen between
+	  may_open and selinux_dentry_open.*/

Typo in the comment (s/of/or/), coding style isn't right for a multi-line comment, and likely needs clarification, e.g.

/*
* 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. */

Quoted 15 lines

security/selinux/hooks.c +3 -0

+	return inode_has_perm(current, inode, file_to_av(file), NULL);
+}
+
 /* task security operations */
 
 static int selinux_task_create(unsigned long clone_flags)

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/fs/open.c linux-2.6.22/fs/open.c

fs/open.c +0 -0

@@ -696,8 +696,13 @@ static struct file *__dentry_open(struct
 	f->f_op = fops_get(inode->i_fop);
 	file_move(f, &inode->i_sb->s_files);
 

fs/open.c static struct file *__dentry_open(struct · line 705

Quoted 7 lines

fs/open.c +5 -0

+	error = security_dentry_open(f);
+	if (error)
+		goto cleanup_all;
+
 	if (!open && f->f_op)
 		open = f->f_op->open;
+

Extraneous whitespace leftover from prior version of the patch.

Quoted 12 lines

fs/open.c +0 -0

 	if (open) {
 		error = open(inode, f);
 		if (error)

diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/include/linux/security.h linux-2.6.22/include/linux/security.h

include/linux/security.h +1 -0

@@ -503,6 +503,11 @@ struct request_sock;
  *	@file contains the file structure being received.
  *	Return 0 if permission is granted.
  *
+ * Security hook for dentry

include/linux/security.h struct request_sock; · line 510

Quoted 4 lines

include/linux/security.h +4 -0

+ *
+ * @dentry_open
+ *   Check permission or get additional information before opening dentry.
+ *

More precisely, "Save open-time permission checking state for later use upon file_permission, and recheck access if anything has changed since inode_permission."

Signature · 2 lines

Stephen Smalley
National Security Agency