Smack: Bring-up access mode

People keep asking me for permissive mode, and I keep saying "no".

Permissive mode is wrong for more reasons than I can enumerate,
but the compelling one is that it's once on, never off.

Nonetheless, there is an argument to be made for running a
process with lots of permissions, logging which are required,
and then locking the process down. There wasn't a way to do
that with Smack, but this provides it.

The notion is that you start out by giving the process an
appropriate Smack label, such as "ATBirds". You create rules
with a wide range of access and the "b" mode. On Tizen it
might be:

	ATBirds	System	rwxalb
	ATBirds	User	rwxalb
	ATBirds	_	rwxalb
	User	ATBirds	wb
	System	ATBirds	wb

Accesses that fail will generate audit records. Accesses
that succeed because of rules marked with a "b" generate
log messages identifying the rule, the program and as much
object information as is convenient.

When the system is properly configured and the programs
brought in line with the labeling scheme the "b" mode can
be removed from the rules. When the system is ready for
production the facility can be configured out.

This provides the developer the convenience of permissive
mode without creating a system that looks like it is
enforcing a policy while it is not.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 56a1439786a9..49a2248b525c 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -304,6 +304,10 @@ static int smk_perm_from_str(const char *string)
                 case 'L':
                         perm |= MAY_LOCK;
                         break;
+                case 'b':
+                case 'B':
+                        perm |= MAY_BRINGUP;
+                        break;
                 default:
                         return perm;
                 }
@@ -616,6 +620,8 @@ static void smk_rule_show(struct seq_file *s, struct smack_rule *srp, int max)
                 seq_putc(s, 't');
         if (srp->smk_access & MAY_LOCK)
                 seq_putc(s, 'l');
+        if (srp->smk_access & MAY_BRINGUP)
+                seq_putc(s, 'b');
 
         seq_putc(s, '\n');
 }
@@ -1880,7 +1886,10 @@ static ssize_t smk_user_access(struct file *file, const char __user *buf,
         else if (res != -ENOENT)
                 return -EINVAL;
 
-        data[0] = res == 0 ? '1' : '0';
+        /*
+         * smk_access() can return a value > 0 in the "bringup" case.
+         */
+        data[0] = res >= 0 ? '1' : '0';
         data[1] = '\0';
 
         simple_transaction_set(file, 2);