linux-kernel - [patch 1/1] selinux: do not clear f

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Message-Id: <1195653696.759.29.camel@moss-spartans.epoch.ncsc.mil>
Date:	Wed, 21 Nov 2007 09:01:36 -0500
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Alexey Dobriyan <adobriyan@...ru>, akpm@...l.org,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	devel@...nvz.org, James Morris <jmorris@...ei.org>,
	Eric Paris <eparis@...isplace.org>
Subject: [patch 1/1] selinux:  do not clear f_op when removing entries

On Tue, 2007-11-20 at 15:17 +0000, Christoph Hellwig wrote:
> On Tue, Nov 20, 2007 at 10:05:05AM -0500, Stephen Smalley wrote:
> > > Nice, getting rid of this is a very good step formwards.  Unfortunately
> > > we have another copy of this junk in
> > > security/selinux/selinuxfs.c:sel_remove_entries() which would need the
> > > same treatment.
> > 
> > Can't just be dropped completely for selinux - we need a way to drop
> > obsolete entries from the prior policy when we load a new policy.
> > 
> > Is the only real problem here the clearing of f_op?  If so, we can
> > likely remove that from sel_remove_entries() without harm, and fix the
> > checks for it to use something more reliable.
> 
> f_op removal is the biggest issue.  It can't really work and this is the
> last instance.  But in general having some half-backed attempts at revoke
> is never a good idea.

Do not clear f_op when removing entries since it isn't safe to do.

Signed-off-by:  Stephen Smalley <sds@...ho.nsa.gov>

---

 security/selinux/selinuxfs.c |   28 +---------------------------
 1 file changed, 1 insertion(+), 27 deletions(-)

diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index f5f3e6d..ac6fe99 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -838,10 +838,6 @@ static ssize_t sel_read_bool(struct file *filep, char __user *buf,
 
 	ret = -EFAULT;
 
-	/* check to see if this file has been deleted */
-	if (!filep->f_op)
-		goto out;
-
 	if (count > PAGE_SIZE) {
 		ret = -EINVAL;
 		goto out;
@@ -882,10 +878,6 @@ static ssize_t sel_write_bool(struct file *filep, const char __user *buf,
 	if (length)
 		goto out;
 
-	/* check to see if this file has been deleted */
-	if (!filep->f_op)
-		goto out;
-
 	if (count >= PAGE_SIZE) {
 		length = -ENOMEM;
 		goto out;
@@ -940,10 +932,6 @@ static ssize_t sel_commit_bools_write(struct file *filep,
 	if (length)
 		goto out;
 
-	/* check to see if this file has been deleted */
-	if (!filep->f_op)
-		goto out;
-
 	if (count >= PAGE_SIZE) {
 		length = -ENOMEM;
 		goto out;
@@ -982,11 +970,9 @@ static const struct file_operations sel_commit_bools_ops = {
 	.write          = sel_commit_bools_write,
 };
 
-/* partial revoke() from fs/proc/generic.c proc_kill_inodes */
 static void sel_remove_entries(struct dentry *de)
 {
-	struct list_head *p, *node;
-	struct super_block *sb = de->d_sb;
+	struct list_head *node;
 
 	spin_lock(&dcache_lock);
 	node = de->d_subdirs.next;
@@ -1006,18 +992,6 @@ static void sel_remove_entries(struct dentry *de)
 	}
 
 	spin_unlock(&dcache_lock);
-
-	file_list_lock();
-	list_for_each(p, &sb->s_files) {
-		struct file * filp = list_entry(p, struct file, f_u.fu_list);
-		struct dentry * dentry = filp->f_path.dentry;
-
-		if (dentry->d_parent != de) {
-			continue;
-		}
-		filp->f_op = NULL;
-	}
-	file_list_unlock();
 }
 
 #define BOOL_DIR_NAME "booleans"


-- 
Stephen Smalley
National Security Agency

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