CRED: Make execve() take advantage of copy-on-write credentials
[linux-3.10.git] / kernel / cred.c
index 833244a7cb058dd2f7bd35f531ebd47ee00754b3..e6fcdd67b2ec94bde93d4a9c4c4e3e37bbef3238 100644 (file)
 #include <linux/keyctl.h>
 #include <linux/init_task.h>
 #include <linux/security.h>
+#include <linux/cn_proc.h>
+#include "cred-internals.h"
+
+static struct kmem_cache *cred_jar;
+
+/*
+ * The common credentials for the initial task's thread group
+ */
+#ifdef CONFIG_KEYS
+static struct thread_group_cred init_tgcred = {
+       .usage  = ATOMIC_INIT(2),
+       .tgid   = 0,
+       .lock   = SPIN_LOCK_UNLOCKED,
+};
+#endif
 
 /*
  * The initial credentials for the initial task
@@ -28,8 +43,41 @@ struct cred init_cred = {
        .cap_bset               = CAP_INIT_BSET,
        .user                   = INIT_USER,
        .group_info             = &init_groups,
+#ifdef CONFIG_KEYS
+       .tgcred                 = &init_tgcred,
+#endif
 };
 
+/*
+ * Dispose of the shared task group credentials
+ */
+#ifdef CONFIG_KEYS
+static void release_tgcred_rcu(struct rcu_head *rcu)
+{
+       struct thread_group_cred *tgcred =
+               container_of(rcu, struct thread_group_cred, rcu);
+
+       BUG_ON(atomic_read(&tgcred->usage) != 0);
+
+       key_put(tgcred->session_keyring);
+       key_put(tgcred->process_keyring);
+       kfree(tgcred);
+}
+#endif
+
+/*
+ * Release a set of thread group credentials.
+ */
+static void release_tgcred(struct cred *cred)
+{
+#ifdef CONFIG_KEYS
+       struct thread_group_cred *tgcred = cred->tgcred;
+
+       if (atomic_dec_and_test(&tgcred->usage))
+               call_rcu(&tgcred->rcu, release_tgcred_rcu);
+#endif
+}
+
 /*
  * The RCU callback to actually dispose of a set of credentials
  */
@@ -37,60 +85,366 @@ static void put_cred_rcu(struct rcu_head *rcu)
 {
        struct cred *cred = container_of(rcu, struct cred, rcu);
 
-       BUG_ON(atomic_read(&cred->usage) != 0);
+       if (atomic_read(&cred->usage) != 0)
+               panic("CRED: put_cred_rcu() sees %p with usage %d\n",
+                     cred, atomic_read(&cred->usage));
 
+       security_cred_free(cred);
        key_put(cred->thread_keyring);
        key_put(cred->request_key_auth);
+       release_tgcred(cred);
        put_group_info(cred->group_info);
        free_uid(cred->user);
-       security_cred_free(cred);
-       kfree(cred);
+       kmem_cache_free(cred_jar, cred);
 }
 
 /**
  * __put_cred - Destroy a set of credentials
- * @sec: The record to release
+ * @cred: The record to release
  *
  * Destroy a set of credentials on which no references remain.
  */
 void __put_cred(struct cred *cred)
 {
+       BUG_ON(atomic_read(&cred->usage) != 0);
+
        call_rcu(&cred->rcu, put_cred_rcu);
 }
 EXPORT_SYMBOL(__put_cred);
 
+/**
+ * prepare_creds - Prepare a new set of credentials for modification
+ *
+ * Prepare a new set of task credentials for modification.  A task's creds
+ * shouldn't generally be modified directly, therefore this function is used to
+ * prepare a new copy, which the caller then modifies and then commits by
+ * calling commit_creds().
+ *
+ * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
+ *
+ * Call commit_creds() or abort_creds() to clean up.
+ */
+struct cred *prepare_creds(void)
+{
+       struct task_struct *task = current;
+       const struct cred *old;
+       struct cred *new;
+
+       BUG_ON(atomic_read(&task->cred->usage) < 1);
+
+       new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
+       if (!new)
+               return NULL;
+
+       old = task->cred;
+       memcpy(new, old, sizeof(struct cred));
+
+       atomic_set(&new->usage, 1);
+       get_group_info(new->group_info);
+       get_uid(new->user);
+
+#ifdef CONFIG_KEYS
+       key_get(new->thread_keyring);
+       key_get(new->request_key_auth);
+       atomic_inc(&new->tgcred->usage);
+#endif
+
+#ifdef CONFIG_SECURITY
+       new->security = NULL;
+#endif
+
+       if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
+               goto error;
+       return new;
+
+error:
+       abort_creds(new);
+       return NULL;
+}
+EXPORT_SYMBOL(prepare_creds);
+
+/*
+ * Prepare credentials for current to perform an execve()
+ * - The caller must hold current->cred_exec_mutex
+ */
+struct cred *prepare_exec_creds(void)
+{
+       struct thread_group_cred *tgcred = NULL;
+       struct cred *new;
+
+#ifdef CONFIG_KEYS
+       tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
+       if (!tgcred)
+               return NULL;
+#endif
+
+       new = prepare_creds();
+       if (!new) {
+               kfree(tgcred);
+               return new;
+       }
+
+#ifdef CONFIG_KEYS
+       /* newly exec'd tasks don't get a thread keyring */
+       key_put(new->thread_keyring);
+       new->thread_keyring = NULL;
+
+       /* create a new per-thread-group creds for all this set of threads to
+        * share */
+       memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
+
+       atomic_set(&tgcred->usage, 1);
+       spin_lock_init(&tgcred->lock);
+
+       /* inherit the session keyring; new process keyring */
+       key_get(tgcred->session_keyring);
+       tgcred->process_keyring = NULL;
+
+       release_tgcred(new);
+       new->tgcred = tgcred;
+#endif
+
+       return new;
+}
+
+/*
+ * prepare new credentials for the usermode helper dispatcher
+ */
+struct cred *prepare_usermodehelper_creds(void)
+{
+#ifdef CONFIG_KEYS
+       struct thread_group_cred *tgcred = NULL;
+#endif
+       struct cred *new;
+
+#ifdef CONFIG_KEYS
+       tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
+       if (!tgcred)
+               return NULL;
+#endif
+
+       new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
+       if (!new)
+               return NULL;
+
+       memcpy(new, &init_cred, sizeof(struct cred));
+
+       atomic_set(&new->usage, 1);
+       get_group_info(new->group_info);
+       get_uid(new->user);
+
+#ifdef CONFIG_KEYS
+       new->thread_keyring = NULL;
+       new->request_key_auth = NULL;
+       new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
+
+       atomic_set(&tgcred->usage, 1);
+       spin_lock_init(&tgcred->lock);
+       new->tgcred = tgcred;
+#endif
+
+#ifdef CONFIG_SECURITY
+       new->security = NULL;
+#endif
+       if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
+               goto error;
+
+       BUG_ON(atomic_read(&new->usage) != 1);
+       return new;
+
+error:
+       put_cred(new);
+       return NULL;
+}
+
 /*
  * Copy credentials for the new process created by fork()
+ *
+ * We share if we can, but under some circumstances we have to generate a new
+ * set.
  */
 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 {
-       struct cred *pcred;
-       int ret;
+#ifdef CONFIG_KEYS
+       struct thread_group_cred *tgcred;
+#endif
+       struct cred *new;
 
-       pcred = kmemdup(p->cred, sizeof(*p->cred), GFP_KERNEL);
-       if (!pcred)
+       mutex_init(&p->cred_exec_mutex);
+
+       if (
+#ifdef CONFIG_KEYS
+               !p->cred->thread_keyring &&
+#endif
+               clone_flags & CLONE_THREAD
+           ) {
+               get_cred(p->cred);
+               atomic_inc(&p->cred->user->processes);
+               return 0;
+       }
+
+       new = prepare_creds();
+       if (!new)
                return -ENOMEM;
 
-#ifdef CONFIG_SECURITY
-       pcred->security = NULL;
+#ifdef CONFIG_KEYS
+       /* new threads get their own thread keyrings if their parent already
+        * had one */
+       if (new->thread_keyring) {
+               key_put(new->thread_keyring);
+               new->thread_keyring = NULL;
+               if (clone_flags & CLONE_THREAD)
+                       install_thread_keyring_to_cred(new);
+       }
+
+       /* we share the process and session keyrings between all the threads in
+        * a process - this is slightly icky as we violate COW credentials a
+        * bit */
+       if (!(clone_flags & CLONE_THREAD)) {
+               tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
+               if (!tgcred) {
+                       put_cred(new);
+                       return -ENOMEM;
+               }
+               atomic_set(&tgcred->usage, 1);
+               spin_lock_init(&tgcred->lock);
+               tgcred->process_keyring = NULL;
+               tgcred->session_keyring = key_get(new->tgcred->session_keyring);
+
+               release_tgcred(new);
+               new->tgcred = tgcred;
+       }
 #endif
 
-       ret = security_cred_alloc(pcred);
-       if (ret < 0) {
-               kfree(pcred);
-               return ret;
+       atomic_inc(&new->user->processes);
+       p->cred = new;
+       return 0;
+}
+
+/**
+ * commit_creds - Install new credentials upon the current task
+ * @new: The credentials to be assigned
+ *
+ * Install a new set of credentials to the current task, using RCU to replace
+ * the old set.
+ *
+ * This function eats the caller's reference to the new credentials.
+ *
+ * Always returns 0 thus allowing this function to be tail-called at the end
+ * of, say, sys_setgid().
+ */
+int commit_creds(struct cred *new)
+{
+       struct task_struct *task = current;
+       const struct cred *old;
+
+       BUG_ON(atomic_read(&new->usage) < 1);
+       BUG_ON(atomic_read(&task->cred->usage) < 1);
+
+       old = task->cred;
+       security_commit_creds(new, old);
+
+       /* dumpability changes */
+       if (old->euid != new->euid ||
+           old->egid != new->egid ||
+           old->fsuid != new->fsuid ||
+           old->fsgid != new->fsgid ||
+           !cap_issubset(new->cap_permitted, old->cap_permitted)) {
+               set_dumpable(task->mm, suid_dumpable);
+               task->pdeath_signal = 0;
+               smp_wmb();
        }
 
-       atomic_set(&pcred->usage, 1);
-       get_group_info(pcred->group_info);
-       get_uid(pcred->user);
-       key_get(pcred->thread_keyring);
-       key_get(pcred->request_key_auth);
+       /* alter the thread keyring */
+       if (new->fsuid != old->fsuid)
+               key_fsuid_changed(task);
+       if (new->fsgid != old->fsgid)
+               key_fsgid_changed(task);
 
-       atomic_inc(&pcred->user->processes);
+       /* do it
+        * - What if a process setreuid()'s and this brings the
+        *   new uid over his NPROC rlimit?  We can check this now
+        *   cheaply with the new uid cache, so if it matters
+        *   we should be checking for it.  -DaveM
+        */
+       if (new->user != old->user)
+               atomic_inc(&new->user->processes);
+       rcu_assign_pointer(task->cred, new);
+       if (new->user != old->user)
+               atomic_dec(&old->user->processes);
 
-       /* RCU assignment is unneeded here as no-one can have accessed this
-        * pointer yet, barring us */
-       p->cred = pcred;
+       sched_switch_user(task);
+
+       /* send notifications */
+       if (new->uid   != old->uid  ||
+           new->euid  != old->euid ||
+           new->suid  != old->suid ||
+           new->fsuid != old->fsuid)
+               proc_id_connector(task, PROC_EVENT_UID);
+
+       if (new->gid   != old->gid  ||
+           new->egid  != old->egid ||
+           new->sgid  != old->sgid ||
+           new->fsgid != old->fsgid)
+               proc_id_connector(task, PROC_EVENT_GID);
+
+       put_cred(old);
        return 0;
 }
+EXPORT_SYMBOL(commit_creds);
+
+/**
+ * abort_creds - Discard a set of credentials and unlock the current task
+ * @new: The credentials that were going to be applied
+ *
+ * Discard a set of credentials that were under construction and unlock the
+ * current task.
+ */
+void abort_creds(struct cred *new)
+{
+       BUG_ON(atomic_read(&new->usage) < 1);
+       put_cred(new);
+}
+EXPORT_SYMBOL(abort_creds);
+
+/**
+ * override_creds - Temporarily override the current process's credentials
+ * @new: The credentials to be assigned
+ *
+ * Install a set of temporary override credentials on the current process,
+ * returning the old set for later reversion.
+ */
+const struct cred *override_creds(const struct cred *new)
+{
+       const struct cred *old = current->cred;
+
+       rcu_assign_pointer(current->cred, get_cred(new));
+       return old;
+}
+EXPORT_SYMBOL(override_creds);
+
+/**
+ * revert_creds - Revert a temporary credentials override
+ * @old: The credentials to be restored
+ *
+ * Revert a temporary set of override credentials to an old set, discarding the
+ * override set.
+ */
+void revert_creds(const struct cred *old)
+{
+       const struct cred *override = current->cred;
+
+       rcu_assign_pointer(current->cred, old);
+       put_cred(override);
+}
+EXPORT_SYMBOL(revert_creds);
+
+/*
+ * initialise the credentials stuff
+ */
+void __init cred_init(void)
+{
+       /* allocate a slab in which we can store credentials */
+       cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
+                                    0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
+}