Subject: [PATCH] Smack: mmap controls for library containment

  In the embedded world there are often situations
  where libraries are updated from a variety of sources,
  for a variety of reasons, and with any number of
  security characteristics. These differences
  might include privilege required for a given library
  provided interface to function properly, as occurs
  from time to time in graphics libraries. There are
  also cases where it is important to limit use of
  libraries based on the provider of the library and
  the security aware application may make choices
  based on that criteria.

  These issues are addressed by providing an additional
  Smack label that may optionally be assigned to an object,
  the SMACK64MMAP attribute. An mmap operation is allowed
  if there is no such attribute.

  If there is a SMACK64MMAP attribute the mmap is permitted
  only if a subject with that label has all of the access
  permitted a subject with the current task label.

  Security aware applications may from time to time
  wish to reduce their "privilege" to avoid accidental use
  of privilege. One case where this arises is the
  environment in which multiple sources provide libraries
  to perform the same functions. An application may know
  that it should eschew services made available from a
  particular vendor, or of a particular version.

  In support of this a secondary list of Smack rules has
  been added that is local to the task. This list is
  consulted only in the case where the global list has
  approved access. It can only further restrict access.
  Unlike the global last, if no entry is found on the
  local list access is granted. An application can add
  entries to its own list by writing to /smack/load-self.

  The changes appear large as they involve refactoring
  the list handling to accomodate there being more
  than one rule list.

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

1 files changed, 227 insertions, 42 deletions

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 533bf3255d7f..123a499ded37 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -84,6 +84,56 @@ struct inode_smack *new_inode_smack(char *smack)
         return isp;
 }
 
+/**
+ * new_task_smack - allocate a task security blob
+ * @smack: a pointer to the Smack label to use in the blob
+ *
+ * Returns the new blob or NULL if there's no memory available
+ */
+static struct task_smack *new_task_smack(char *task, char *forked, gfp_t gfp)
+{
+        struct task_smack *tsp;
+
+        tsp = kzalloc(sizeof(struct task_smack), gfp);
+        if (tsp == NULL)
+                return NULL;
+
+        tsp->smk_task = task;
+        tsp->smk_forked = forked;
+        INIT_LIST_HEAD(&tsp->smk_rules);
+        mutex_init(&tsp->smk_rules_lock);
+
+        return tsp;
+}
+
+/**
+ * smk_copy_rules - copy a rule set
+ * @nhead - new rules header pointer
+ * @ohead - old rules header pointer
+ *
+ * Returns 0 on success, -ENOMEM on error
+ */
+static int smk_copy_rules(struct list_head *nhead, struct list_head *ohead,
+                                gfp_t gfp)
+{
+        struct smack_rule *nrp;
+        struct smack_rule *orp;
+        int rc = 0;
+
+        INIT_LIST_HEAD(nhead);
+
+        list_for_each_entry_rcu(orp, ohead, list) {
+                nrp = kzalloc(sizeof(struct smack_rule), gfp);
+                if (nrp == NULL) {
+                        rc = -ENOMEM;
+                        break;
+                }
+                *nrp = *orp;
+                list_add_rcu(&nrp->list, nhead);
+        }
+        return rc;
+}
+
 /*
  * LSM hooks.
  * We he, that is fun!
@@ -102,23 +152,17 @@ static int smack_ptrace_access_check(struct task_struct *ctp, unsigned int mode)
 {
         int rc;
         struct smk_audit_info ad;
-        char *sp, *tsp;
+        char *tsp;
 
         rc = cap_ptrace_access_check(ctp, mode);
         if (rc != 0)
                 return rc;
 
-        sp = smk_of_current();
         tsp = smk_of_task(task_security(ctp));
         smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
         smk_ad_setfield_u_tsk(&ad, ctp);
 
-        /* we won't log here, because rc can be overriden */
-        rc = smk_access(sp, tsp, MAY_READWRITE, NULL);
-        if (rc != 0 && capable(CAP_MAC_OVERRIDE))
-                rc = 0;
-
-        smack_log(sp, tsp, MAY_READWRITE, rc, &ad);
+        rc = smk_curacc(tsp, MAY_READWRITE, &ad);
         return rc;
 }
 
@@ -134,23 +178,17 @@ static int smack_ptrace_traceme(struct task_struct *ptp)
 {
         int rc;
         struct smk_audit_info ad;
-        char *sp, *tsp;
+        char *tsp;
 
         rc = cap_ptrace_traceme(ptp);
         if (rc != 0)
                 return rc;
 
+        tsp = smk_of_task(task_security(ptp));
         smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
         smk_ad_setfield_u_tsk(&ad, ptp);
 
-        sp = smk_of_current();
-        tsp = smk_of_task(task_security(ptp));
-        /* we won't log here, because rc can be overriden */
-        rc = smk_access(tsp, sp, MAY_READWRITE, NULL);
-        if (rc != 0 && has_capability(ptp, CAP_MAC_OVERRIDE))
-                rc = 0;
-
-        smack_log(tsp, sp, MAY_READWRITE, rc, &ad);
+        rc = smk_curacc(tsp, MAY_READWRITE, &ad);
         return rc;
 }
 
@@ -474,7 +512,7 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
 {
         char *isp = smk_of_inode(inode);
         char *dsp = smk_of_inode(dir);
-        u32 may;
+        int may;
 
         if (name) {
                 *name = kstrdup(XATTR_SMACK_SUFFIX, GFP_KERNEL);
@@ -483,14 +521,17 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
         }
 
         if (value) {
-                may = smk_access_entry(smk_of_current(), dsp);
+                rcu_read_lock();
+                may = smk_access_entry(smk_of_current(), dsp, &smack_rule_list);
+                rcu_read_unlock();
 
                 /*
                  * If the access rule allows transmutation and
                  * the directory requests transmutation then
                  * by all means transmute.
                  */
-                if (((may & MAY_TRANSMUTE) != 0) && smk_inode_transmutable(dir))
+                if (may > 0 && ((may & MAY_TRANSMUTE) != 0) &&
+                    smk_inode_transmutable(dir))
                         isp = dsp;
 
                 *value = kstrdup(isp, GFP_KERNEL);
@@ -716,7 +757,8 @@ static int smack_inode_setxattr(struct dentry *dentry, const char *name,
         if (strcmp(name, XATTR_NAME_SMACK) == 0 ||
             strcmp(name, XATTR_NAME_SMACKIPIN) == 0 ||
             strcmp(name, XATTR_NAME_SMACKIPOUT) == 0 ||
-            strcmp(name, XATTR_NAME_SMACKEXEC) == 0) {
+            strcmp(name, XATTR_NAME_SMACKEXEC) == 0 ||
+            strcmp(name, XATTR_NAME_SMACKMMAP) == 0) {
                 if (!capable(CAP_MAC_ADMIN))
                         rc = -EPERM;
                 /*
@@ -773,6 +815,12 @@ static void smack_inode_post_setxattr(struct dentry *dentry, const char *name,
                         isp->smk_task = nsp;
                 else
                         isp->smk_task = smack_known_invalid.smk_known;
+        } else if (strcmp(name, XATTR_NAME_SMACKMMAP) == 0) {
+                nsp = smk_import(value, size);
+                if (nsp != NULL)
+                        isp->smk_mmap = nsp;
+                else
+                        isp->smk_mmap = smack_known_invalid.smk_known;
         } else if (strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0)
                 isp->smk_flags |= SMK_INODE_TRANSMUTE;
 
@@ -815,7 +863,8 @@ static int smack_inode_removexattr(struct dentry *dentry, const char *name)
             strcmp(name, XATTR_NAME_SMACKIPIN) == 0 ||
             strcmp(name, XATTR_NAME_SMACKIPOUT) == 0 ||
             strcmp(name, XATTR_NAME_SMACKEXEC) == 0 ||
-            strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0) {
+            strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0 ||
+            strcmp(name, XATTR_NAME_SMACKMMAP)) {
                 if (!capable(CAP_MAC_ADMIN))
                         rc = -EPERM;
         } else
@@ -829,6 +878,7 @@ static int smack_inode_removexattr(struct dentry *dentry, const char *name)
         if (rc == 0) {
                 isp = dentry->d_inode->i_security;
                 isp->smk_task = NULL;
+                isp->smk_mmap = NULL;
         }
 
         return rc;
@@ -1060,6 +1110,113 @@ static int smack_file_fcntl(struct file *file, unsigned int cmd,
 }
 
 /**
+ * smk_mmap_list_check - the mmap check
+ * @sub: subject label
+ * @obj: object label
+ * @access: access mode
+ * @local: the task specific rule list
+ *
+ * Returns 0 if acces is permitted, -EACCES otherwise
+ */
+static int smk_mmap_list_check(char *sub, char *obj, int access,
+                                struct list_head *local)
+{
+        int may;
+
+        /*
+         * If there is not a global rule that
+         * allows access say no.
+         */
+        may = smk_access_entry(sub, obj, &smack_rule_list);
+        if (may == -ENOENT || (may & access) != access)
+                return -EACCES;
+        /*
+         * If there is a task local rule that
+         * denies access say no.
+         */
+        may = smk_access_entry(sub, obj, local);
+        if (may != -ENOENT && (may & access) != access)
+                return -EACCES;
+
+        return 0;
+}
+
+/**
+ * smack_file_mmap :
+ * Check permissions for a mmap operation.  The @file may be NULL, e.g.
+ * if mapping anonymous memory.
+ * @file contains the file structure for file to map (may be NULL).
+ * @reqprot contains the protection requested by the application.
+ * @prot contains the protection that will be applied by the kernel.
+ * @flags contains the operational flags.
+ * Return 0 if permission is granted.
+ */
+static int smack_file_mmap(struct file *file,
+                           unsigned long reqprot, unsigned long prot,
+                           unsigned long flags, unsigned long addr,
+                           unsigned long addr_only)
+{
+        struct smack_rule *srp;
+        struct task_smack *tsp;
+        char *sp;
+        char *msmack;
+        struct inode_smack *isp;
+        struct dentry *dp;
+        int rc;
+
+        /* do DAC check on address space usage */
+        rc = cap_file_mmap(file, reqprot, prot, flags, addr, addr_only);
+        if (rc || addr_only)
+                return rc;
+
+        if (file == NULL || file->f_dentry == NULL)
+                return 0;
+
+        dp = file->f_dentry;
+
+        if (dp->d_inode == NULL)
+                return 0;
+
+        isp = dp->d_inode->i_security;
+        if (isp->smk_mmap == NULL)
+                return 0;
+        msmack = isp->smk_mmap;
+
+        tsp = current_security();
+        sp = smk_of_current();
+        rc = 0;
+
+        rcu_read_lock();
+        /*
+         * For each Smack rule associated with the subject
+         * label verify that the SMACK64MMAP also has access
+         * to that rule's object label.
+         *
+         * Because neither of the labels comes
+         * from the networking code it is sufficient
+         * to compare pointers.
+         */
+        list_for_each_entry_rcu(srp, &smack_rule_list, list) {
+                if (srp->smk_subject != sp)
+                        continue;
+                /*
+                 * Matching labels always allows access.
+                 */
+                if (msmack == srp->smk_object)
+                        continue;
+
+                rc = smk_mmap_list_check(msmack, srp->smk_object,
+                                         srp->smk_access, &tsp->smk_rules);
+                if (rc != 0)
+                        break;
+        }
+
+        rcu_read_unlock();
+
+        return rc;
+}
+
+/**
  * smack_file_set_fowner - set the file security blob value
  * @file: object in question
  *
@@ -1095,6 +1252,7 @@ static int smack_file_send_sigiotask(struct task_struct *tsk,
          * struct fown_struct is never outside the context of a struct file
          */
         file = container_of(fown, struct file, f_owner);
+
         /* we don't log here as rc can be overriden */
         rc = smk_access(file->f_security, tsp, MAY_WRITE, NULL);
         if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE))
@@ -1145,9 +1303,14 @@ static int smack_file_receive(struct file *file)
  */
 static int smack_cred_alloc_blank(struct cred *cred, gfp_t gfp)
 {
-        cred->security = kzalloc(sizeof(struct task_smack), gfp);
-        if (cred->security == NULL)
+        struct task_smack *tsp;
+
+        tsp = new_task_smack(NULL, NULL, gfp);
+        if (tsp == NULL)
                 return -ENOMEM;
+
+        cred->security = tsp;
+
         return 0;
 }
 
@@ -1156,13 +1319,24 @@ static int smack_cred_alloc_blank(struct cred *cred, gfp_t gfp)
  * smack_cred_free - "free" task-level security credentials
  * @cred: the credentials in question
  *
- * Smack isn't using copies of blobs. Everyone
- * points to an immutable list. The blobs never go away.
- * There is no leak here.
  */
 static void smack_cred_free(struct cred *cred)
 {
-        kfree(cred->security);
+        struct task_smack *tsp = cred->security;
+        struct smack_rule *rp;
+        struct list_head *l;
+        struct list_head *n;
+
+        if (tsp == NULL)
+                return;
+        cred->security = NULL;
+
+        list_for_each_safe(l, n, &tsp->smk_rules) {
+                rp = list_entry(l, struct smack_rule, list);
+                list_del(&rp->list);
+                kfree(rp);
+        }
+        kfree(tsp);
 }
 
 /**
@@ -1178,13 +1352,16 @@ static int smack_cred_prepare(struct cred *new, const struct cred *old,
 {
         struct task_smack *old_tsp = old->security;
         struct task_smack *new_tsp;
+        int rc;
 
-        new_tsp = kzalloc(sizeof(struct task_smack), gfp);
+        new_tsp = new_task_smack(old_tsp->smk_task, old_tsp->smk_task, gfp);
         if (new_tsp == NULL)
                 return -ENOMEM;
 
-        new_tsp->smk_task = old_tsp->smk_task;
-        new_tsp->smk_forked = old_tsp->smk_task;
+        rc = smk_copy_rules(&new_tsp->smk_rules, &old_tsp->smk_rules, gfp);
+        if (rc != 0)
+                return rc;
+
         new->security = new_tsp;
         return 0;
 }
@@ -1203,6 +1380,11 @@ static void smack_cred_transfer(struct cred *new, const struct cred *old)
 
         new_tsp->smk_task = old_tsp->smk_task;
         new_tsp->smk_forked = old_tsp->smk_task;
+        mutex_init(&new_tsp->smk_rules_lock);
+        INIT_LIST_HEAD(&new_tsp->smk_rules);
+
+
+        /* cbs copy rule list */
 }
 
 /**
@@ -2419,6 +2601,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
                         }
                 }
                 isp->smk_task = smk_fetch(XATTR_NAME_SMACKEXEC, inode, dp);
+                isp->smk_mmap = smk_fetch(XATTR_NAME_SMACKMMAP, inode, dp);
 
                 dput(dp);
                 break;
@@ -2478,6 +2661,7 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
 static int smack_setprocattr(struct task_struct *p, char *name,
                              void *value, size_t size)
 {
+        int rc;
         struct task_smack *tsp;
         struct task_smack *oldtsp;
         struct cred *new;
@@ -2513,13 +2697,16 @@ static int smack_setprocattr(struct task_struct *p, char *name,
         new = prepare_creds();
         if (new == NULL)
                 return -ENOMEM;
-        tsp = kzalloc(sizeof(struct task_smack), GFP_KERNEL);
+
+        tsp = new_task_smack(newsmack, oldtsp->smk_forked, GFP_KERNEL);
         if (tsp == NULL) {
                 kfree(new);
                 return -ENOMEM;
         }
-        tsp->smk_task = newsmack;
-        tsp->smk_forked = oldtsp->smk_forked;
+        rc = smk_copy_rules(&tsp->smk_rules, &oldtsp->smk_rules, GFP_KERNEL);
+        if (rc != 0)
+                return rc;
+
         new->security = tsp;
         commit_creds(new);
         return size;
@@ -3221,6 +3408,7 @@ struct security_operations smack_ops = {
         .file_ioctl =                   smack_file_ioctl,
         .file_lock =                    smack_file_lock,
         .file_fcntl =                   smack_file_fcntl,
+        .file_mmap =                    smack_file_mmap,
         .file_set_fowner =              smack_file_set_fowner,
         .file_send_sigiotask =          smack_file_send_sigiotask,
         .file_receive =                 smack_file_receive,
@@ -3334,23 +3522,20 @@ static __init int smack_init(void)
         struct cred *cred;
         struct task_smack *tsp;
 
-        tsp = kzalloc(sizeof(struct task_smack), GFP_KERNEL);
+        if (!security_module_enable(&smack_ops))
+                return 0;
+
+        tsp = new_task_smack(smack_known_floor.smk_known,
+                                smack_known_floor.smk_known, GFP_KERNEL);
         if (tsp == NULL)
                 return -ENOMEM;
 
-        if (!security_module_enable(&smack_ops)) {
-                kfree(tsp);
-                return 0;
-        }
-
         printk(KERN_INFO "Smack:  Initializing.\n");
 
         /*
          * Set the security state for the initial task.
          */
         cred = (struct cred *) current->cred;
-        tsp->smk_forked = smack_known_floor.smk_known;
-        tsp->smk_task = smack_known_floor.smk_known;
         cred->security = tsp;
 
         /* initialize the smack_know_list */