Smack: Implement lock security mode
Linux file locking does not follow the same rules
as other mechanisms. Even though it is a write operation
a process can set a read lock on files which it has open
only for read access. Two programs with read access to
a file can use read locks to communicate.
This is not acceptable in a Mandatory Access Control
environment. Smack treats setting a read lock as the
write operation that it is. Unfortunately, many programs
assume that setting a read lock is a read operation.
These programs are unhappy in the Smack environment.
This patch introduces a new access mode (lock) to address
this problem. A process with lock access to a file can
set a read lock. A process with write access to a file can
set a read lock or a write lock. This prevents a situation
where processes are granted write access just so they can
set read locks.
Targeted for git://git.gitorious.org/smack-next/kernel.git
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index b3b59b1..14293cd 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -84,6 +84,8 @@
*
* Do the object check first because that is more
* likely to differ.
+ *
+ * Allowing write access implies allowing locking.
*/
int smk_access_entry(char *subject_label, char *object_label,
struct list_head *rule_list)
@@ -99,6 +101,11 @@
}
}
+ /*
+ * MAY_WRITE implies MAY_LOCK.
+ */
+ if ((may & MAY_WRITE) == MAY_WRITE)
+ may |= MAY_LOCK;
return may;
}
@@ -245,6 +252,7 @@
static inline void smack_str_from_perm(char *string, int access)
{
int i = 0;
+
if (access & MAY_READ)
string[i++] = 'r';
if (access & MAY_WRITE)
@@ -255,6 +263,8 @@
string[i++] = 'a';
if (access & MAY_TRANSMUTE)
string[i++] = 't';
+ if (access & MAY_LOCK)
+ string[i++] = 'l';
string[i] = '\0';
}
/**