Smack: Allow an unconfined label in bringup mode

I have vehemently opposed adding a "permissive" mode to Smack
for the simple reasons that it would be subject to massive abuse
and that developers refuse to turn it off come product release.
I still believe that this is true, and still refuse to add a
general "permissive mode". So don't ask again.

Bumjin Im suggested an approach that addresses most of the concerns,
and I have implemented it here. I still believe that we'd be better
off without this sort of thing, but it looks like this minimizes the
abuse potential.

Firstly, you have to configure Smack Bringup Mode. That allows
for "release" software to be ammune from abuse. Second, only one
label gets to be "permissive" at a time. You can use it for
debugging, but that's about it.

A label written to smackfs/unconfined is treated specially.
If either the subject or object label of an access check
matches the "unconfined" label, and the access would not
have been allowed otherwise an audit record and a console
message are generated. The audit record "request" string is
marked with either "(US)" or "(UO)", to indicate that the
request was granted because of an unconfined label. The
fact that an inode was accessed by an unconfined label is
remembered, and subsequent accesses to that "impure"
object are noted in the log. The impurity is not stored in
the filesystem, so a file mislabled as a side effect of
using an unconfined label may still cause concern after
a reboot.

So, it's there, it's dangerous, but so many application
developers seem incapable of living without it I have
given in. I've tried to make it as safe as I can, but
in the end it's still a chain saw.

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

security/smack/smack.h

@@ -105,6 +105,7 @@ struct task_smack {
 #define	SMK_INODE_INSTANT	0x01	/* inode is instantiated */
 #define	SMK_INODE_TRANSMUTE	0x02	/* directory is transmuting */
 #define	SMK_INODE_CHANGED	0x04	/* smack was transmuted */
+#define	SMK_INODE_IMPURE	0x08	/* involved in an impure transaction */
 
 /*
  * A label access rule.
@@ -193,6 +194,10 @@ struct smk_port_label {
 #define MAY_LOCK	0x00002000	/* Locks should be writes, but ... */
 #define MAY_BRINGUP	0x00004000	/* Report use of this rule */
 
+#define SMACK_BRINGUP_ALLOW		1	/* Allow bringup mode */
+#define SMACK_UNCONFINED_SUBJECT	2	/* Allow unconfined label */
+#define SMACK_UNCONFINED_OBJECT		3	/* Allow unconfined label */
+
 /*
  * Just to make the common cases easier to deal with
  */
@@ -254,6 +259,9 @@ extern int smack_cipso_mapped;
 extern struct smack_known *smack_net_ambient;
 extern struct smack_known *smack_onlycap;
 extern struct smack_known *smack_syslog_label;
+#ifdef CONFIG_SECURITY_SMACK_BRINGUP
+extern struct smack_known *smack_unconfined;
+#endif
 extern struct smack_known smack_cipso_option;
 extern int smack_ptrace_rule;
 

security/smack/smack_access.c

@@ -130,7 +130,8 @@ int smk_access(struct smack_known *subject, struct smack_known *object,
 
 	/*
 	 * Hardcoded comparisons.
-	 *
+	 */
+	/*
 	 * A star subject can't access any object.
 	 */
 	if (subject == &smack_known_star) {
@@ -189,10 +190,20 @@ int smk_access(struct smack_known *subject, struct smack_known *object,
 	 * succeed because of "b" rules.
 	 */
 	if (may & MAY_BRINGUP)
-		rc = MAY_BRINGUP;
+		rc = SMACK_BRINGUP_ALLOW;
 #endif
 
 out_audit:
+
+#ifdef CONFIG_SECURITY_SMACK_BRINGUP
+	if (rc < 0) {
+		if (object == smack_unconfined)
+			rc = SMACK_UNCONFINED_OBJECT;
+		if (subject == smack_unconfined)
+			rc = SMACK_UNCONFINED_SUBJECT;
+	}
+#endif
+
 #ifdef CONFIG_AUDIT
 	if (a)
 		smack_log(subject->smk_known, object->smk_known,
@@ -338,19 +349,16 @@ static void smack_log_callback(struct audit_buffer *ab, void *a)
 void smack_log(char *subject_label, char *object_label, int request,
 	       int result, struct smk_audit_info *ad)
 {
+#ifdef CONFIG_SECURITY_SMACK_BRINGUP
+	char request_buffer[SMK_NUM_ACCESS_TYPE + 5];
+#else
 	char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
+#endif
 	struct smack_audit_data *sad;
 	struct common_audit_data *a = &ad->a;
 
-#ifdef CONFIG_SECURITY_SMACK_BRINGUP
-	/*
-	 * The result may be positive in bringup mode.
-	 */
-	if (result > 0)
-		result = 0;
-#endif
 	/* check if we have to log the current event */
-	if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
+	if (result < 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
 		return;
 	if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
 		return;
@@ -364,6 +372,21 @@ void smack_log(char *subject_label, char *object_label, int request,
 	smack_str_from_perm(request_buffer, request);
 	sad->subject = subject_label;
 	sad->object  = object_label;
+#ifdef CONFIG_SECURITY_SMACK_BRINGUP
+	/*
+	 * The result may be positive in bringup mode.
+	 * A positive result is an allow, but not for normal reasons.
+	 * Mark it as successful, but don't filter it out even if
+	 * the logging policy says to do so.
+	 */
+	if (result == SMACK_UNCONFINED_SUBJECT)
+		strcat(request_buffer, "(US)");
+	else if (result == SMACK_UNCONFINED_OBJECT)
+		strcat(request_buffer, "(UO)");
+
+	if (result > 0)
+		result = 0;
+#endif
 	sad->request = request_buffer;
 	sad->result  = result;
 

security/smack/smack_lsm.c

@@ -57,6 +57,13 @@ static struct kmem_cache *smack_inode_cache;
 int smack_enabled;
 
 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
+static char *smk_bu_mess[] = {
+	"Bringup Error",	/* Unused */
+	"Bringup",		/* SMACK_BRINGUP_ALLOW */
+	"Unconfined Subject",	/* SMACK_UNCONFINED_SUBJECT */
+	"Unconfined Object",	/* SMACK_UNCONFINED_OBJECT */
+};
+
 static void smk_bu_mode(int mode, char *s)
 {
 	int i = 0;
@@ -87,9 +94,11 @@ static int smk_bu_note(char *note, struct smack_known *sskp,
 
 	if (rc <= 0)
 		return rc;
+	if (rc > SMACK_UNCONFINED_OBJECT)
+		rc = 0;
 
 	smk_bu_mode(mode, acc);
-	pr_info("Smack Bringup: (%s %s %s) %s\n",
+	pr_info("Smack %s: (%s %s %s) %s\n", smk_bu_mess[rc],
 		sskp->smk_known, oskp->smk_known, acc, note);
 	return 0;
 }
@@ -106,9 +115,11 @@ static int smk_bu_current(char *note, struct smack_known *oskp,
 
 	if (rc <= 0)
 		return rc;
+	if (rc > SMACK_UNCONFINED_OBJECT)
+		rc = 0;
 
 	smk_bu_mode(mode, acc);
-	pr_info("Smack Bringup: (%s %s %s) %s %s\n",
+	pr_info("Smack %s: (%s %s %s) %s %s\n", smk_bu_mess[rc],
 		tsp->smk_task->smk_known, oskp->smk_known,
 		acc, current->comm, note);
 	return 0;
@@ -126,9 +137,11 @@ static int smk_bu_task(struct task_struct *otp, int mode, int rc)
 
 	if (rc <= 0)
 		return rc;
+	if (rc > SMACK_UNCONFINED_OBJECT)
+		rc = 0;
 
 	smk_bu_mode(mode, acc);
-	pr_info("Smack Bringup: (%s %s %s) %s to %s\n",
+	pr_info("Smack %s: (%s %s %s) %s to %s\n", smk_bu_mess[rc],
 		tsp->smk_task->smk_known, smk_task->smk_known, acc,
 		current->comm, otp->comm);
 	return 0;
@@ -141,14 +154,25 @@ static int smk_bu_task(struct task_struct *otp, int mode, int rc)
 static int smk_bu_inode(struct inode *inode, int mode, int rc)
 {
 	struct task_smack *tsp = current_security();
+	struct inode_smack *isp = inode->i_security;
 	char acc[SMK_NUM_ACCESS_TYPE + 1];
 
+	if (isp->smk_flags & SMK_INODE_IMPURE)
+		pr_info("Smack Unconfined Corruption: inode=(%s %ld) %s\n",
+			inode->i_sb->s_id, inode->i_ino, current->comm);
+
 	if (rc <= 0)
 		return rc;
+	if (rc > SMACK_UNCONFINED_OBJECT)
+		rc = 0;
+	if (rc == SMACK_UNCONFINED_SUBJECT &&
+	    (mode & (MAY_WRITE | MAY_APPEND)))
+		isp->smk_flags |= SMK_INODE_IMPURE;
 
 	smk_bu_mode(mode, acc);
-	pr_info("Smack Bringup: (%s %s %s) inode=(%s %ld) %s\n",
-		tsp->smk_task->smk_known, smk_of_inode(inode)->smk_known, acc,
+
+	pr_info("Smack %s: (%s %s %s) inode=(%s %ld) %s\n", smk_bu_mess[rc],
+		tsp->smk_task->smk_known, isp->smk_inode->smk_known, acc,
 		inode->i_sb->s_id, inode->i_ino, current->comm);
 	return 0;
 }
@@ -162,13 +186,20 @@ static int smk_bu_file(struct file *file, int mode, int rc)
 	struct task_smack *tsp = current_security();
 	struct smack_known *sskp = tsp->smk_task;
 	struct inode *inode = file_inode(file);
+	struct inode_smack *isp = inode->i_security;
 	char acc[SMK_NUM_ACCESS_TYPE + 1];
 
+	if (isp->smk_flags & SMK_INODE_IMPURE)
+		pr_info("Smack Unconfined Corruption: inode=(%s %ld) %s\n",
+			inode->i_sb->s_id, inode->i_ino, current->comm);
+
 	if (rc <= 0)
 		return rc;
+	if (rc > SMACK_UNCONFINED_OBJECT)
+		rc = 0;
 
 	smk_bu_mode(mode, acc);
-	pr_info("Smack Bringup: (%s %s %s) file=(%s %ld %pD) %s\n",
+	pr_info("Smack %s: (%s %s %s) file=(%s %ld %pD) %s\n", smk_bu_mess[rc],
 		sskp->smk_known, smk_of_inode(inode)->smk_known, acc,
 		inode->i_sb->s_id, inode->i_ino, file,
 		current->comm);
@@ -185,13 +216,20 @@ static int smk_bu_credfile(const struct cred *cred, struct file *file,
 	struct task_smack *tsp = cred->security;
 	struct smack_known *sskp = tsp->smk_task;
 	struct inode *inode = file->f_inode;
+	struct inode_smack *isp = inode->i_security;
 	char acc[SMK_NUM_ACCESS_TYPE + 1];
 
+	if (isp->smk_flags & SMK_INODE_IMPURE)
+		pr_info("Smack Unconfined Corruption: inode=(%s %ld) %s\n",
+			inode->i_sb->s_id, inode->i_ino, current->comm);
+
 	if (rc <= 0)
 		return rc;
+	if (rc > SMACK_UNCONFINED_OBJECT)
+		rc = 0;
 
 	smk_bu_mode(mode, acc);
-	pr_info("Smack Bringup: (%s %s %s) file=(%s %ld %pD) %s\n",
+	pr_info("Smack %s: (%s %s %s) file=(%s %ld %pD) %s\n", smk_bu_mess[rc],
 		sskp->smk_known, smk_of_inode(inode)->smk_known, acc,
 		inode->i_sb->s_id, inode->i_ino, file,
 		current->comm);

security/smack/smackfs.c

@@ -54,6 +54,9 @@ enum smk_inos {
 	SMK_CHANGE_RULE	= 19,	/* change or add rules (long labels) */
 	SMK_SYSLOG	= 20,	/* change syslog label) */
 	SMK_PTRACE	= 21,	/* set ptrace rule */
+#ifdef CONFIG_SECURITY_SMACK_BRINGUP
+	SMK_UNCONFINED	= 22,	/* define an unconfined label */
+#endif
 };
 
 /*
@@ -95,6 +98,16 @@ int smack_cipso_mapped = SMACK_CIPSO_MAPPED_DEFAULT;
  */
 struct smack_known *smack_onlycap;
 
+#ifdef CONFIG_SECURITY_SMACK_BRINGUP
+/*
+ * Allow one label to be unconfined. This is for
+ * debugging and application bring-up purposes only.
+ * It is bad and wrong, but everyone seems to expect
+ * to have it.
+ */
+struct smack_known *smack_unconfined;
+#endif
+
 /*
  * If this value is set restrict syslog use to the label specified.
  * It can be reset via smackfs/syslog
@@ -1717,6 +1730,85 @@ static const struct file_operations smk_onlycap_ops = {
 	.llseek		= default_llseek,
 };
 
+#ifdef CONFIG_SECURITY_SMACK_BRINGUP
+/**
+ * smk_read_unconfined - read() for smackfs/unconfined
+ * @filp: file pointer, not actually used
+ * @buf: where to put the result
+ * @cn: maximum to send along
+ * @ppos: where to start
+ *
+ * Returns number of bytes read or error code, as appropriate
+ */
+static ssize_t smk_read_unconfined(struct file *filp, char __user *buf,
+					size_t cn, loff_t *ppos)
+{
+	char *smack = "";
+	ssize_t rc = -EINVAL;
+	int asize;
+
+	if (*ppos != 0)
+		return 0;
+
+	if (smack_unconfined != NULL)
+		smack = smack_unconfined->smk_known;
+
+	asize = strlen(smack) + 1;
+
+	if (cn >= asize)
+		rc = simple_read_from_buffer(buf, cn, ppos, smack, asize);
+
+	return rc;
+}
+
+/**
+ * smk_write_unconfined - write() for smackfs/unconfined
+ * @file: file pointer, not actually used
+ * @buf: where to get the data from
+ * @count: bytes sent
+ * @ppos: where to start
+ *
+ * Returns number of bytes written or error code, as appropriate
+ */
+static ssize_t smk_write_unconfined(struct file *file, const char __user *buf,
+					size_t count, loff_t *ppos)
+{
+	char *data;
+	int rc = count;
+
+	if (!smack_privileged(CAP_MAC_ADMIN))
+		return -EPERM;
+
+	data = kzalloc(count + 1, GFP_KERNEL);
+	if (data == NULL)
+		return -ENOMEM;
+
+	/*
+	 * Should the null string be passed in unset the unconfined value.
+	 * This seems like something to be careful with as usually
+	 * smk_import only expects to return NULL for errors. It
+	 * is usually the case that a nullstring or "\n" would be
+	 * bad to pass to smk_import but in fact this is useful here.
+	 *
+	 * smk_import will also reject a label beginning with '-',
+	 * so "-confine" will also work.
+	 */
+	if (copy_from_user(data, buf, count) != 0)
+		rc = -EFAULT;
+	else
+		smack_unconfined = smk_import_entry(data, count);
+
+	kfree(data);
+	return rc;
+}
+
+static const struct file_operations smk_unconfined_ops = {
+	.read		= smk_read_unconfined,
+	.write		= smk_write_unconfined,
+	.llseek		= default_llseek,
+};
+#endif /* CONFIG_SECURITY_SMACK_BRINGUP */
+
 /**
  * smk_read_logging - read() for /smack/logging
  * @filp: file pointer, not actually used
@@ -2384,6 +2476,10 @@ static int smk_fill_super(struct super_block *sb, void *data, int silent)
 			"syslog", &smk_syslog_ops, S_IRUGO|S_IWUSR},
 		[SMK_PTRACE] = {
 			"ptrace", &smk_ptrace_ops, S_IRUGO|S_IWUSR},
+#ifdef CONFIG_SECURITY_SMACK_BRINGUP
+		[SMK_UNCONFINED] = {
+			"unconfined", &smk_unconfined_ops, S_IRUGO|S_IWUSR},
+#endif
 		/* last one */
 			{""}
 	};