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>

1 files changed, 8 insertions, 2 deletions

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 80f4b4a45725..160aa08e3cd5 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -139,7 +139,7 @@ const char *smack_cipso_option = SMACK_CIPSO_OPTION;
  * SMK_LOADLEN: Smack rule length
  */
 #define SMK_OACCESS	"rwxa"
-#define SMK_ACCESS	"rwxat"
+#define SMK_ACCESS	"rwxatl"
 #define SMK_OACCESSLEN	(sizeof(SMK_OACCESS) - 1)
 #define SMK_ACCESSLEN	(sizeof(SMK_ACCESS) - 1)
 #define SMK_OLOADLEN	(SMK_LABELLEN + SMK_LABELLEN + SMK_OACCESSLEN)
@@ -282,6 +282,10 @@ static int smk_perm_from_str(const char *string)
 		case 'T':
 			perm |= MAY_TRANSMUTE;
 			break;
+		case 'l':
+		case 'L':
+			perm |= MAY_LOCK;
+			break;
 		default:
 			return perm;
 		}
@@ -452,7 +456,7 @@ static ssize_t smk_write_rules_list(struct file *file, const char __user *buf,
 		/*
 		 * Minor hack for backward compatibility
 		 */
-		if (count != SMK_OLOADLEN && count != SMK_LOADLEN)
+		if (count < SMK_OLOADLEN || count > SMK_LOADLEN)
 			return -EINVAL;
 	} else {
 		if (count >= PAGE_SIZE) {
@@ -592,6 +596,8 @@ static void smk_rule_show(struct seq_file *s, struct smack_rule *srp, int max)
 		seq_putc(s, 'a');
 	if (srp->smk_access & MAY_TRANSMUTE)
 		seq_putc(s, 't');
+	if (srp->smk_access & MAY_LOCK)
+		seq_putc(s, 'l');
 
 	seq_putc(s, '\n');
 }