TOMOYO: Add refcounter on domain structure.
Tetsuo Handa [Thu, 11 Feb 2010 00:43:20 +0000 (09:43 +0900)]
Add refcounter to "struct tomoyo_domain_info" since garbage collector needs to
determine whether this struct is referred by "struct cred"->security or not.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/tomoyo/common.h
security/tomoyo/domain.c
security/tomoyo/tomoyo.c

index f6aff59..521b4b5 100644 (file)
@@ -234,6 +234,10 @@ struct tomoyo_acl_info {
  *      name of the domain to be created was too long or it could not allocate
  *      memory. If set to true, more than one process continued execve()
  *      without domain transition.
+ *  (9) "users" is an atomic_t that holds how many "struct cred"->security
+ *      are referring this "struct tomoyo_domain_info". If is_deleted == true
+ *      and users == 0, this struct will be kfree()d upon next garbage
+ *      collection.
  *
  * A domain's lifecycle is an analogy of files on / directory.
  * Multiple domains with the same domainname cannot be created (as with
@@ -252,6 +256,7 @@ struct tomoyo_domain_info {
        bool quota_warned; /* Quota warnning flag.   */
        bool ignore_global_allow_read; /* Ignore "allow_read" flag. */
        bool transition_failed; /* Domain transition failed flag. */
+       atomic_t users; /* Number of referring credentials. */
 };
 
 /*
index d60b8a6..6f74b30 100644 (file)
@@ -817,6 +817,8 @@ int tomoyo_find_next_domain(struct linux_binprm *bprm)
  out:
        if (!domain)
                domain = old_domain;
+       /* Update reference count on "struct tomoyo_domain_info". */
+       atomic_inc(&domain->users);
        bprm->cred->security = domain;
        kfree(real_program_name);
        kfree(symlink_program_name);
index 8a0988d..87e82bf 100644 (file)
@@ -21,21 +21,23 @@ static int tomoyo_cred_alloc_blank(struct cred *new, gfp_t gfp)
 static int tomoyo_cred_prepare(struct cred *new, const struct cred *old,
                               gfp_t gfp)
 {
-       /*
-        * Since "struct tomoyo_domain_info *" is a sharable pointer,
-        * we don't need to duplicate.
-        */
-       new->security = old->security;
+       struct tomoyo_domain_info *domain = old->security;
+       new->security = domain;
+       if (domain)
+               atomic_inc(&domain->users);
        return 0;
 }
 
 static void tomoyo_cred_transfer(struct cred *new, const struct cred *old)
 {
-       /*
-        * Since "struct tomoyo_domain_info *" is a sharable pointer,
-        * we don't need to duplicate.
-        */
-       new->security = old->security;
+       tomoyo_cred_prepare(new, old, 0);
+}
+
+static void tomoyo_cred_free(struct cred *cred)
+{
+       struct tomoyo_domain_info *domain = cred->security;
+       if (domain)
+               atomic_dec(&domain->users);
 }
 
 static int tomoyo_bprm_set_creds(struct linux_binprm *bprm)
@@ -59,6 +61,14 @@ static int tomoyo_bprm_set_creds(struct linux_binprm *bprm)
        if (!tomoyo_policy_loaded)
                tomoyo_load_policy(bprm->filename);
        /*
+        * Release reference to "struct tomoyo_domain_info" stored inside
+        * "bprm->cred->security". New reference to "struct tomoyo_domain_info"
+        * stored inside "bprm->cred->security" will be acquired later inside
+        * tomoyo_find_next_domain().
+        */
+       atomic_dec(&((struct tomoyo_domain_info *)
+                    bprm->cred->security)->users);
+       /*
         * Tell tomoyo_bprm_check_security() is called for the first time of an
         * execve operation.
         */
@@ -75,12 +85,6 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm)
         * using current domain.
         */
        if (!domain) {
-               /*
-                * We will need to protect whole execve() operation when GC
-                * starts kfree()ing "struct tomoyo_domain_info" because
-                * bprm->cred->security points to "struct tomoyo_domain_info"
-                * but "struct tomoyo_domain_info" does not have a refcounter.
-                */
                const int idx = tomoyo_read_lock();
                const int err = tomoyo_find_next_domain(bprm);
                tomoyo_read_unlock(idx);
@@ -265,6 +269,7 @@ static struct security_operations tomoyo_security_ops = {
        .cred_alloc_blank    = tomoyo_cred_alloc_blank,
        .cred_prepare        = tomoyo_cred_prepare,
        .cred_transfer       = tomoyo_cred_transfer,
+       .cred_free           = tomoyo_cred_free,
        .bprm_set_creds      = tomoyo_bprm_set_creds,
        .bprm_check_security = tomoyo_bprm_check_security,
        .file_fcntl          = tomoyo_file_fcntl,