linux-kernel - [PATCH] Smackv8: Safe lockless {cipso,load} read operation

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Message-ID: <20071021022543.GB3091@Ahmed>
Date:	Sun, 21 Oct 2007 04:25:43 +0200
From:	"Ahmed S. Darwish" <darwish.07@...il.com>
To:	Casey Schaufler <casey@...aufler-ca.com>,
	Al Viro <viro@....linux.org.uk>
Cc:	torvalds@...l.org, akpm@...l.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Smackv8: Safe lockless {cipso,load} read operation

Hi,

Utilizing Al's concers about using smack_cipso_count without locking,
here's a patch that remove smack_cipso_count and uses simple list 
traversing in read() without any counting mechanism.

CC: Al Viro <viro@....linux.org.uk>
Signed-off-by: Ahmed S. Darwish <darwish.07@...il.com>

---

Please apply over omit-non-cipso-lables-in-cipso-seq-start.patch
Using smack_{list,cipso}_count in the read context was useless
anyway cause we were just traversing the list.

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index b061cd0..c38d0d0 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -63,16 +63,17 @@ int smack_cipso_direct = SMACK_CIPSO_DIRECT_DEFAULT;
 
 static int smk_cipso_doi_value = SMACK_CIPSO_DOI_DEFAULT;
 static int smack_list_count;
-static int smack_cipso_count;
 struct smk_list_entry *smack_list;
 
+#define SEQ_READ_FINISHED	1
+
 /*
  * Seq_file read operations for /smack/load
  */
 
 static void *load_seq_start(struct seq_file *s, loff_t *pos)
 {
-	if (*pos >= smack_list_count)
+	if (*pos == SEQ_READ_FINISHED)
 		return NULL;
 
 	return smack_list;
@@ -80,8 +81,13 @@ static void *load_seq_start(struct seq_file *s, loff_t *pos)
 
 static void *load_seq_next(struct seq_file *s, void *v, loff_t *pos)
 {
-	(*pos)++;
-	return ((struct smk_list_entry *) v)->smk_next;
+	struct smk_list_entry *skp = ((struct smk_list_entry *) v)->smk_next;
+
+	if (skp)
+		return skp;
+
+	*pos = SEQ_READ_FINISHED;
+	return NULL;
 }
 
 static int load_seq_show(struct seq_file *s, void *v)
@@ -306,7 +312,7 @@ static void *cipso_seq_start(struct seq_file *s, loff_t *pos)
 {
 	struct smack_known *skp = smack_known;
 
-	if (*pos >= smack_cipso_count)
+	if (*pos == SEQ_READ_FINISHED)
 		return NULL;
 
 	while (skp && !skp->smk_cipso)
@@ -319,12 +325,14 @@ static void *cipso_seq_next(struct seq_file *s, void *v, loff_t *pos)
 {
 	struct smack_known *skp = ((struct smack_known *) v)->smk_next;
 
-	(*pos)++;
-
 	while (skp && !skp->smk_cipso)
 		skp = skp->smk_next;
 
-	return skp;
+	if (skp)
+		return skp;
+
+	*pos = SEQ_READ_FINISHED;
+	return NULL;
 }
 
 /*
@@ -488,7 +496,6 @@ static ssize_t smk_write_cipso(struct file *file, const char __user *buf,
 				rc = -ENOMEM;
 				break;
 			}
-			++smack_cipso_count;
 		} else
 			scp = NULL;
 

-- 
Ahmed S. Darwish
HomePage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com
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