Smack: allow multiple labels in onlycap

Smack onlycap allows limiting of CAP_MAC_ADMIN and CAP_MAC_OVERRIDE to
processes running with the configured label. But having single privileged
label is not enough in some real use cases. On a complex system like Tizen,
there maybe few programs that need to configure Smack policy in run-time
and running them all with a single label is not always practical.
This patch extends onlycap feature for multiple labels. They are configured
in the same smackfs "onlycap" interface, separated by spaces.

Signed-off-by: Rafal Krypa <r.krypa@samsung.com>

3 files changed, 160 insertions, 69 deletions

diff --git a/security/smack/smack.h b/security/smack/smack.h
index b8c1a869d85e..244e035e5a99 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -138,6 +138,11 @@ struct smk_port_label {
         struct smack_known      *smk_out;       /* outgoing label */
 };
 
+struct smack_onlycap {
+        struct list_head        list;
+        struct smack_known      *smk_label;
+};
+
 /*
  * Mount options
  */
@@ -249,6 +254,7 @@ int smk_netlbl_mls(int, char *, struct netlbl_lsm_secattr *, int);
 struct smack_known *smk_import_entry(const char *, int);
 void smk_insert_entry(struct smack_known *skp);
 struct smack_known *smk_find_entry(const char *);
+int smack_privileged(int cap);
 
 /*
  * Shared data.
@@ -257,7 +263,6 @@ extern int smack_enabled;
 extern int smack_cipso_direct;
 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;
@@ -276,6 +281,9 @@ extern struct mutex	smack_known_lock;
 extern struct list_head smack_known_list;
 extern struct list_head smk_netlbladdr_list;
 
+extern struct mutex     smack_onlycap_lock;
+extern struct list_head smack_onlycap_list;
+
 #define SMACK_HASH_SLOTS 16
 extern struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];
 
@@ -332,21 +340,6 @@ static inline struct smack_known *smk_of_current(void)
 }
 
 /*
- * Is the task privileged and allowed to be privileged
- * by the onlycap rule.
- */
-static inline int smack_privileged(int cap)
-{
-        struct smack_known *skp = smk_of_current();
-
-        if (!capable(cap))
-                return 0;
-        if (smack_onlycap == NULL || smack_onlycap == skp)
-                return 1;
-        return 0;
-}
-
-/*
  * logging functions
  */
 #define SMACK_AUDIT_DENIED 0x1
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index 408e20be1ad7..00f6b38bffbd 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -617,3 +617,44 @@ struct smack_known *smack_from_secid(const u32 secid)
         rcu_read_unlock();
         return &smack_known_invalid;
 }
+
+/*
+ * Unless a process is running with one of these labels
+ * even having CAP_MAC_OVERRIDE isn't enough to grant
+ * privilege to violate MAC policy. If no labels are
+ * designated (the empty list case) capabilities apply to
+ * everyone.
+ */
+LIST_HEAD(smack_onlycap_list);
+DEFINE_MUTEX(smack_onlycap_lock);
+
+/*
+ * Is the task privileged and allowed to be privileged
+ * by the onlycap rule.
+ *
+ * Returns 1 if the task is allowed to be privileged, 0 if it's not.
+ */
+int smack_privileged(int cap)
+{
+        struct smack_known *skp = smk_of_current();
+        struct smack_onlycap *sop;
+
+        if (!capable(cap))
+                return 0;
+
+        rcu_read_lock();
+        if (list_empty(&smack_onlycap_list)) {
+                rcu_read_unlock();
+                return 1;
+        }
+
+        list_for_each_entry_rcu(sop, &smack_onlycap_list, list) {
+                if (sop->smk_label == skp) {
+                        rcu_read_unlock();
+                        return 1;
+                }
+        }
+        rcu_read_unlock();
+
+        return 0;
+}
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index e40dc48737ff..f1c22a891b1a 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -87,16 +87,6 @@ int smack_cipso_direct = SMACK_CIPSO_DIRECT_DEFAULT;
  */
 int smack_cipso_mapped = SMACK_CIPSO_MAPPED_DEFAULT;
 
-/*
- * Unless a process is running with this label even
- * having CAP_MAC_OVERRIDE isn't enough to grant
- * privilege to violate MAC policy. If no label is
- * designated (the NULL case) capabilities apply to
- * everyone. It is expected that the hat (^) label
- * will be used if any label is used.
- */
-struct smack_known *smack_onlycap;
-
 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
 /*
  * Allow one label to be unconfined. This is for
@@ -1636,34 +1626,79 @@ static const struct file_operations smk_ambient_ops = {
         .llseek         = default_llseek,
 };
 
-/**
- * smk_read_onlycap - read() for smackfs/onlycap
- * @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
+/*
+ * Seq_file operations for /smack/onlycap
  */
-static ssize_t smk_read_onlycap(struct file *filp, char __user *buf,
-                                size_t cn, loff_t *ppos)
+static void *onlycap_seq_start(struct seq_file *s, loff_t *pos)
 {
-        char *smack = "";
-        ssize_t rc = -EINVAL;
-        int asize;
+        return smk_seq_start(s, pos, &smack_onlycap_list);
+}
 
-        if (*ppos != 0)
-                return 0;
+static void *onlycap_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+        return smk_seq_next(s, v, pos, &smack_onlycap_list);
+}
 
-        if (smack_onlycap != NULL)
-                smack = smack_onlycap->smk_known;
+static int onlycap_seq_show(struct seq_file *s, void *v)
+{
+        struct list_head *list = v;
+        struct smack_onlycap *sop =
+                list_entry_rcu(list, struct smack_onlycap, list);
 
-        asize = strlen(smack) + 1;
+        seq_puts(s, sop->smk_label->smk_known);
+        seq_putc(s, ' ');
 
-        if (cn >= asize)
-                rc = simple_read_from_buffer(buf, cn, ppos, smack, asize);
+        return 0;
+}
 
-        return rc;
+static const struct seq_operations onlycap_seq_ops = {
+        .start = onlycap_seq_start,
+        .next  = onlycap_seq_next,
+        .show  = onlycap_seq_show,
+        .stop  = smk_seq_stop,
+};
+
+static int smk_open_onlycap(struct inode *inode, struct file *file)
+{
+        return seq_open(file, &onlycap_seq_ops);
+}
+
+/**
+ * smk_list_swap_rcu - swap public list with a private one in RCU-safe way
+ * The caller must hold appropriate mutex to prevent concurrent modifications
+ * to the public list.
+ * Private list is assumed to be not accessible to other threads yet.
+ *
+ * @public: public list
+ * @private: private list
+ */
+static void smk_list_swap_rcu(struct list_head *public,
+                              struct list_head *private)
+{
+        struct list_head *first, *last;
+
+        if (list_empty(public)) {
+                list_splice_init_rcu(private, public, synchronize_rcu);
+        } else {
+                /* Remember public list before replacing it */
+                first = public->next;
+                last = public->prev;
+
+                /* Publish private list in place of public in RCU-safe way */
+                private->prev->next = public;
+                private->next->prev = public;
+                rcu_assign_pointer(public->next, private->next);
+                public->prev = private->prev;
+
+                synchronize_rcu();
+
+                /* When all readers are done with the old public list,
+                 * attach it in place of private */
+                private->next = first;
+                private->prev = last;
+                first->prev = private;
+                last->next = private;
+        }
 }
 
 /**
@@ -1679,28 +1714,47 @@ static ssize_t smk_write_onlycap(struct file *file, const char __user *buf,
                                  size_t count, loff_t *ppos)
 {
         char *data;
-        struct smack_known *skp = smk_of_task(current->cred->security);
+        char *data_parse;
+        char *tok;
+        struct smack_known *skp;
+        struct smack_onlycap *sop;
+        struct smack_onlycap *sop2;
+        LIST_HEAD(list_tmp);
         int rc = count;
 
         if (!smack_privileged(CAP_MAC_ADMIN))
                 return -EPERM;
 
-        /*
-         * This can be done using smk_access() but is done
-         * explicitly for clarity. The smk_access() implementation
-         * would use smk_access(smack_onlycap, MAY_WRITE)
-         */
-        if (smack_onlycap != NULL && smack_onlycap != skp)
-                return -EPERM;
-
         data = kzalloc(count + 1, GFP_KERNEL);
         if (data == NULL)
                 return -ENOMEM;
 
         if (copy_from_user(data, buf, count) != 0) {
-                rc = -EFAULT;
-                goto freeout;
+                kfree(data);
+                return -EFAULT;
+        }
+
+        data_parse = data;
+        while ((tok = strsep(&data_parse, " ")) != NULL) {
+                if (!*tok)
+                        continue;
+
+                skp = smk_import_entry(tok, 0);
+                if (IS_ERR(skp)) {
+                        rc = PTR_ERR(skp);
+                        break;
+                }
+
+                sop = kzalloc(sizeof(*sop), GFP_KERNEL);
+                if (sop == NULL) {
+                        rc = -ENOMEM;
+                        break;
+                }
+
+                sop->smk_label = skp;
+                list_add_rcu(&sop->list, &list_tmp);
         }
+        kfree(data);
 
         /*
          * Clear the smack_onlycap on invalid label errors. This means
@@ -1710,26 +1764,29 @@ static ssize_t smk_write_onlycap(struct file *file, const char __user *buf,
          * so "-usecapabilities" will also work.
          *
          * But do so only on invalid label, not on system errors.
+         * The invalid label must be first to count as clearing attempt.
          */
-        skp = smk_import_entry(data, count);
-        if (PTR_ERR(skp) == -EINVAL)
-                skp = NULL;
-        else if (IS_ERR(skp)) {
-                rc = PTR_ERR(skp);
-                goto freeout;
+        if (rc == -EINVAL && list_empty(&list_tmp))
+                rc = count;
+
+        if (rc >= 0) {
+                mutex_lock(&smack_onlycap_lock);
+                smk_list_swap_rcu(&smack_onlycap_list, &list_tmp);
+                mutex_unlock(&smack_onlycap_lock);
         }
 
-        smack_onlycap = skp;
+        list_for_each_entry_safe(sop, sop2, &list_tmp, list)
+                kfree(sop);
 
-freeout:
-        kfree(data);
         return rc;
 }
 
 static const struct file_operations smk_onlycap_ops = {
-        .read           = smk_read_onlycap,
+        .open           = smk_open_onlycap,
+        .read           = seq_read,
         .write          = smk_write_onlycap,
-        .llseek         = default_llseek,
+        .llseek         = seq_lseek,
+        .release        = seq_release,
 };
 
 #ifdef CONFIG_SECURITY_SMACK_BRINGUP