3 files changed, 102 insertions, 1 deletions

diff --git a/security/smack/smack.h b/security/smack/smack.h
index 4a4477f5afdc..31dce559595a 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -178,6 +178,7 @@ u32 smack_to_secid(const char *);
 extern int smack_cipso_direct;
 extern int smack_net_nltype;
 extern char *smack_net_ambient;
+extern char *smack_onlycap;
 
 extern struct smack_known *smack_known;
 extern struct smack_known smack_known_floor;
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index f6b5f6eed6dd..79ff21ed4c3b 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -157,7 +157,7 @@ int smk_access(char *subject_label, char *object_label, int request)
  *
  * This function checks the current subject label/object label pair
  * in the access rule list and returns 0 if the access is permitted,
- * non zero otherwise. It allows that current my have the capability
+ * non zero otherwise. It allows that current may have the capability
  * to override the rules.
  */
 int smk_curacc(char *obj_label, u32 mode)
@@ -168,6 +168,14 @@ int smk_curacc(char *obj_label, u32 mode)
         if (rc == 0)
                 return 0;
 
+        /*
+         * Return if a specific label has been designated as the
+         * only one that gets privilege and current does not
+         * have that label.
+         */
+        if (smack_onlycap != NULL && smack_onlycap != current->security)
+                return rc;
+
         if (capable(CAP_MAC_OVERRIDE))
                 return 0;
 
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 271a835fbbe3..e7c642458ec9 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -39,6 +39,7 @@ enum smk_inos {
         SMK_DIRECT      = 6,    /* CIPSO level indicating direct label */
         SMK_AMBIENT     = 7,    /* internet ambient label */
         SMK_NLTYPE      = 8,    /* label scheme to use by default */
+        SMK_ONLYCAP     = 9,    /* the only "capable" label */
 };
 
 /*
@@ -68,6 +69,16 @@ int smack_net_nltype = NETLBL_NLTYPE_CIPSOV4;
  */
 int smack_cipso_direct = SMACK_CIPSO_DIRECT_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.
+ */
+char *smack_onlycap;
+
 static int smk_cipso_doi_value = SMACK_CIPSO_DOI_DEFAULT;
 struct smk_list_entry *smack_list;
 
@@ -787,6 +798,85 @@ static const struct file_operations smk_ambient_ops = {
         .write          = smk_write_ambient,
 };
 
+/**
+ * smk_read_onlycap - read() for /smack/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
+ */
+static ssize_t smk_read_onlycap(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_onlycap != NULL)
+                smack = smack_onlycap;
+
+        asize = strlen(smack) + 1;
+
+        if (cn >= asize)
+                rc = simple_read_from_buffer(buf, cn, ppos, smack, asize);
+
+        return rc;
+}
+
+/**
+ * smk_write_onlycap - write() for /smack/onlycap
+ * @filp: 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_onlycap(struct file *file, const char __user *buf,
+                                 size_t count, loff_t *ppos)
+{
+        char in[SMK_LABELLEN];
+        char *sp = current->security;
+
+        if (!capable(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 != sp)
+                return -EPERM;
+
+        if (count >= SMK_LABELLEN)
+                return -EINVAL;
+
+        if (copy_from_user(in, buf, count) != 0)
+                return -EFAULT;
+
+        /*
+         * Should the null string be passed in unset the onlycap 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.
+         */
+        smack_onlycap = smk_import(in, count);
+
+        return count;
+}
+
+static const struct file_operations smk_onlycap_ops = {
+        .read           = smk_read_onlycap,
+        .write          = smk_write_onlycap,
+};
+
 struct option_names {
         int     o_number;
         char    *o_name;
@@ -919,6 +1009,8 @@ static int smk_fill_super(struct super_block *sb, void *data, int silent)
                         {"ambient", &smk_ambient_ops, S_IRUGO|S_IWUSR},
                 [SMK_NLTYPE]    =
                         {"nltype", &smk_nltype_ops, S_IRUGO|S_IWUSR},
+                [SMK_ONLYCAP]   =
+                        {"onlycap", &smk_onlycap_ops, S_IRUGO|S_IWUSR},
                 /* last one */ {""}
         };