/* Task credentials management - see Documentation/credentials.txt

   *
   * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public Licence
   * as published by the Free Software Foundation; either version
   * 2 of the Licence, or (at your option) any later version.
   */
  #include <linux/module.h>
  #include <linux/cred.h>
  #include <linux/sched.h>
  #include <linux/key.h>
  #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
   */
  struct cred init_cred = {

  	.usage			= ATOMIC_INIT(4),

  	.securebits		= SECUREBITS_DEFAULT,
  	.cap_inheritable	= CAP_INIT_INH_SET,
  	.cap_permitted		= CAP_FULL_SET,
  	.cap_effective		= CAP_INIT_EFF_SET,
  	.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
   */
  static void put_cred_rcu(struct rcu_head *rcu)
  {
  	struct cred *cred = container_of(rcu, struct cred, rcu);

  	if (atomic_read(&cred->usage) != 0)
  		panic("CRED: put_cred_rcu() sees %p with usage %d
  ",
  		      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);

  	kmem_cache_free(cred_jar, cred);

  }
  
  /**
   * __put_cred - Destroy a set of credentials

   * @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().
   *

   * Preparation involves making a copy of the objective creds for modification.
   *

   * 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->real_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.

   *
   * The new process gets the current process's subjective credentials as its
   * objective and subjective credentials

   */
  int copy_creds(struct task_struct *p, unsigned long clone_flags)
  {

  #ifdef CONFIG_KEYS
  	struct thread_group_cred *tgcred;
  #endif
  	struct cred *new;

  	int ret;

  
  	mutex_init(&p->cred_exec_mutex);

  	if (
  #ifdef CONFIG_KEYS
  		!p->cred->thread_keyring &&
  #endif
  		clone_flags & CLONE_THREAD
  	    ) {

  		p->real_cred = get_cred(p->cred);

  		get_cred(p->cred);
  		atomic_inc(&p->cred->user->processes);
  		return 0;
  	}
  
  	new = prepare_creds();
  	if (!new)

  		return -ENOMEM;

  	if (clone_flags & CLONE_NEWUSER) {
  		ret = create_user_ns(new);
  		if (ret < 0)
  			goto error_put;
  	}

  #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) {

  			ret = -ENOMEM;
  			goto error_put;

  		}

  		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

  	atomic_inc(&new->user->processes);

  	p->cred = p->real_cred = get_cred(new);

  	return 0;

  
  error_put:
  	put_cred(new);
  	return ret;

  }

  /**
   * 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.  Both the objective and the subjective credentials pointers are
   * updated.  This function may not be called if the subjective credentials are
   * in an overridden state.

   *
   * 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(task->cred != task->real_cred);
  	BUG_ON(atomic_read(&task->real_cred->usage) < 2);

  	BUG_ON(atomic_read(&new->usage) < 1);

  	old = task->real_cred;

  	security_commit_creds(new, old);

  	get_cred(new); /* we will require a ref for the subj creds too */

  	/* 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();

  	}

  	/* alter the thread keyring */
  	if (new->fsuid != old->fsuid)
  		key_fsuid_changed(task);
  	if (new->fsgid != old->fsgid)
  		key_fsgid_changed(task);
  
  	/* 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->real_cred, new);

  	rcu_assign_pointer(task->cred, new);
  	if (new->user != old->user)
  		atomic_dec(&old->user->processes);
  
  	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);

  	/* release the old obj and subj refs both */
  	put_cred(old);

  	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 - Override the current process's subjective credentials

   * @new: The credentials to be assigned
   *

   * Install a set of temporary override subjective 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 subjective credentials override

   * @old: The credentials to be restored
   *

   * Revert a temporary set of override subjective 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);
  }

  
  /**
   * prepare_kernel_cred - Prepare a set of credentials for a kernel service
   * @daemon: A userspace daemon to be used as a reference
   *
   * Prepare a set of credentials for a kernel service.  This can then be used to
   * override a task's own credentials so that work can be done on behalf of that
   * task that requires a different subjective context.
   *
   * @daemon is used to provide a base for the security record, but can be NULL.
   * If @daemon is supplied, then the security data will be derived from that;
   * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
   *
   * The caller may change these controls afterwards if desired.
   *
   * Returns the new credentials or NULL if out of memory.
   *
   * Does not take, and does not return holding current->cred_replace_mutex.
   */
  struct cred *prepare_kernel_cred(struct task_struct *daemon)
  {
  	const struct cred *old;
  	struct cred *new;
  
  	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
  	if (!new)
  		return NULL;
  
  	if (daemon)
  		old = get_task_cred(daemon);
  	else
  		old = get_cred(&init_cred);
  
  	get_uid(new->user);
  	get_group_info(new->group_info);
  
  #ifdef CONFIG_KEYS
  	atomic_inc(&init_tgcred.usage);
  	new->tgcred = &init_tgcred;
  	new->request_key_auth = NULL;
  	new->thread_keyring = NULL;
  	new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
  #endif
  
  #ifdef CONFIG_SECURITY
  	new->security = NULL;
  #endif
  	if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
  		goto error;
  
  	atomic_set(&new->usage, 1);
  	put_cred(old);
  	return new;
  
  error:
  	put_cred(new);
  	return NULL;
  }
  EXPORT_SYMBOL(prepare_kernel_cred);
  
  /**
   * set_security_override - Set the security ID in a set of credentials
   * @new: The credentials to alter
   * @secid: The LSM security ID to set
   *
   * Set the LSM security ID in a set of credentials so that the subjective
   * security is overridden when an alternative set of credentials is used.
   */
  int set_security_override(struct cred *new, u32 secid)
  {
  	return security_kernel_act_as(new, secid);
  }
  EXPORT_SYMBOL(set_security_override);
  
  /**
   * set_security_override_from_ctx - Set the security ID in a set of credentials
   * @new: The credentials to alter
   * @secctx: The LSM security context to generate the security ID from.
   *
   * Set the LSM security ID in a set of credentials so that the subjective
   * security is overridden when an alternative set of credentials is used.  The
   * security ID is specified in string form as a security context to be
   * interpreted by the LSM.
   */
  int set_security_override_from_ctx(struct cred *new, const char *secctx)
  {
  	u32 secid;
  	int ret;
  
  	ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
  	if (ret < 0)
  		return ret;
  
  	return set_security_override(new, secid);
  }
  EXPORT_SYMBOL(set_security_override_from_ctx);
  
  /**
   * set_create_files_as - Set the LSM file create context in a set of credentials
   * @new: The credentials to alter
   * @inode: The inode to take the context from
   *
   * Change the LSM file creation context in a set of credentials to be the same
   * as the object context of the specified inode, so that the new inodes have
   * the same MAC context as that inode.
   */
  int set_create_files_as(struct cred *new, struct inode *inode)
  {
  	new->fsuid = inode->i_uid;
  	new->fsgid = inode->i_gid;
  	return security_kernel_create_files_as(new, inode);
  }
  EXPORT_SYMBOL(set_create_files_as);