xref: /openbmc/linux/security/keys/process_keys.c (revision 05bcf503)

/* Manage a process's keyrings
 *
 * Copyright (C) 2004-2005, 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 License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/keyctl.h>
#include <linux/fs.h>
#include <linux/err.h>
#include <linux/mutex.h>
#include <linux/security.h>
#include <linux/user_namespace.h>
#include <asm/uaccess.h>
#include "internal.h"

/* Session keyring create vs join semaphore */
static DEFINE_MUTEX(key_session_mutex);

/* User keyring creation semaphore */
static DEFINE_MUTEX(key_user_keyring_mutex);

/* The root user's tracking struct */
struct key_user root_key_user = {
	.usage		= ATOMIC_INIT(3),
	.cons_lock	= __MUTEX_INITIALIZER(root_key_user.cons_lock),
	.lock		= __SPIN_LOCK_UNLOCKED(root_key_user.lock),
	.nkeys		= ATOMIC_INIT(2),
	.nikeys		= ATOMIC_INIT(2),
	.uid		= GLOBAL_ROOT_UID,
};

/*
 * Install the user and user session keyrings for the current process's UID.
 */
int install_user_keyrings(void)
{
	struct user_struct *user;
	const struct cred *cred;
	struct key *uid_keyring, *session_keyring;
	char buf[20];
	int ret;
	uid_t uid;

	cred = current_cred();
	user = cred->user;
	uid = from_kuid(cred->user_ns, user->uid);

	kenter("%p{%u}", user, uid);

	if (user->uid_keyring) {
		kleave(" = 0 [exist]");
		return 0;
	}

	mutex_lock(&key_user_keyring_mutex);
	ret = 0;

	if (!user->uid_keyring) {
		/* get the UID-specific keyring
		 * - there may be one in existence already as it may have been
		 *   pinned by a session, but the user_struct pointing to it
		 *   may have been destroyed by setuid */
		sprintf(buf, "_uid.%u", uid);

		uid_keyring = find_keyring_by_name(buf, true);
		if (IS_ERR(uid_keyring)) {
			uid_keyring = keyring_alloc(buf, user->uid, INVALID_GID,
						    cred, KEY_ALLOC_IN_QUOTA,
						    NULL);
			if (IS_ERR(uid_keyring)) {
				ret = PTR_ERR(uid_keyring);
				goto error;
			}
		}

		/* get a default session keyring (which might also exist
		 * already) */
		sprintf(buf, "_uid_ses.%u", uid);

		session_keyring = find_keyring_by_name(buf, true);
		if (IS_ERR(session_keyring)) {
			session_keyring =
				keyring_alloc(buf, user->uid, INVALID_GID,
					      cred, KEY_ALLOC_IN_QUOTA, NULL);
			if (IS_ERR(session_keyring)) {
				ret = PTR_ERR(session_keyring);
				goto error_release;
			}

			/* we install a link from the user session keyring to
			 * the user keyring */
			ret = key_link(session_keyring, uid_keyring);
			if (ret < 0)
				goto error_release_both;
		}

		/* install the keyrings */
		user->uid_keyring = uid_keyring;
		user->session_keyring = session_keyring;
	}

	mutex_unlock(&key_user_keyring_mutex);
	kleave(" = 0");
	return 0;

error_release_both:
	key_put(session_keyring);
error_release:
	key_put(uid_keyring);
error:
	mutex_unlock(&key_user_keyring_mutex);
	kleave(" = %d", ret);
	return ret;
}

/*
 * Install a fresh thread keyring directly to new credentials.  This keyring is
 * allowed to overrun the quota.
 */
int install_thread_keyring_to_cred(struct cred *new)
{
	struct key *keyring;

	keyring = keyring_alloc("_tid", new->uid, new->gid, new,
				KEY_ALLOC_QUOTA_OVERRUN, NULL);
	if (IS_ERR(keyring))
		return PTR_ERR(keyring);

	new->thread_keyring = keyring;
	return 0;
}

/*
 * Install a fresh thread keyring, discarding the old one.
 */
static int install_thread_keyring(void)
{
	struct cred *new;
	int ret;

	new = prepare_creds();
	if (!new)
		return -ENOMEM;

	BUG_ON(new->thread_keyring);

	ret = install_thread_keyring_to_cred(new);
	if (ret < 0) {
		abort_creds(new);
		return ret;
	}

	return commit_creds(new);
}

/*
 * Install a process keyring directly to a credentials struct.
 *
 * Returns -EEXIST if there was already a process keyring, 0 if one installed,
 * and other value on any other error
 */
int install_process_keyring_to_cred(struct cred *new)
{
	struct key *keyring;
	int ret;

	if (new->tgcred->process_keyring)
		return -EEXIST;

	keyring = keyring_alloc("_pid", new->uid, new->gid,
				new, KEY_ALLOC_QUOTA_OVERRUN, NULL);
	if (IS_ERR(keyring))
		return PTR_ERR(keyring);

	spin_lock_irq(&new->tgcred->lock);
	if (!new->tgcred->process_keyring) {
		new->tgcred->process_keyring = keyring;
		keyring = NULL;
		ret = 0;
	} else {
		ret = -EEXIST;
	}
	spin_unlock_irq(&new->tgcred->lock);
	key_put(keyring);
	return ret;
}

/*
 * Make sure a process keyring is installed for the current process.  The
 * existing process keyring is not replaced.
 *
 * Returns 0 if there is a process keyring by the end of this function, some
 * error otherwise.
 */
static int install_process_keyring(void)
{
	struct cred *new;
	int ret;

	new = prepare_creds();
	if (!new)
		return -ENOMEM;

	ret = install_process_keyring_to_cred(new);
	if (ret < 0) {
		abort_creds(new);
		return ret != -EEXIST ? ret : 0;
	}

	return commit_creds(new);
}

/*
 * Install a session keyring directly to a credentials struct.
 */
int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
{
	unsigned long flags;
	struct key *old;

	might_sleep();

	/* create an empty session keyring */
	if (!keyring) {
		flags = KEY_ALLOC_QUOTA_OVERRUN;
		if (cred->tgcred->session_keyring)
			flags = KEY_ALLOC_IN_QUOTA;

		keyring = keyring_alloc("_ses", cred->uid, cred->gid,
					cred, flags, NULL);
		if (IS_ERR(keyring))
			return PTR_ERR(keyring);
	} else {
		atomic_inc(&keyring->usage);
	}

	/* install the keyring */
	spin_lock_irq(&cred->tgcred->lock);
	old = cred->tgcred->session_keyring;
	rcu_assign_pointer(cred->tgcred->session_keyring, keyring);
	spin_unlock_irq(&cred->tgcred->lock);

	/* we're using RCU on the pointer, but there's no point synchronising
	 * on it if it didn't previously point to anything */
	if (old) {
		synchronize_rcu();
		key_put(old);
	}

	return 0;
}

/*
 * Install a session keyring, discarding the old one.  If a keyring is not
 * supplied, an empty one is invented.
 */
static int install_session_keyring(struct key *keyring)
{
	struct cred *new;
	int ret;

	new = prepare_creds();
	if (!new)
		return -ENOMEM;

	ret = install_session_keyring_to_cred(new, keyring);
	if (ret < 0) {
		abort_creds(new);
		return ret;
	}

	return commit_creds(new);
}

/*
 * Handle the fsuid changing.
 */
void key_fsuid_changed(struct task_struct *tsk)
{
	/* update the ownership of the thread keyring */
	BUG_ON(!tsk->cred);
	if (tsk->cred->thread_keyring) {
		down_write(&tsk->cred->thread_keyring->sem);
		tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
		up_write(&tsk->cred->thread_keyring->sem);
	}
}

/*
 * Handle the fsgid changing.
 */
void key_fsgid_changed(struct task_struct *tsk)
{
	/* update the ownership of the thread keyring */
	BUG_ON(!tsk->cred);
	if (tsk->cred->thread_keyring) {
		down_write(&tsk->cred->thread_keyring->sem);
		tsk->cred->thread_keyring->gid = tsk->cred->fsgid;
		up_write(&tsk->cred->thread_keyring->sem);
	}
}

/*
 * Search the process keyrings attached to the supplied cred for the first
 * matching key.
 *
 * The search criteria are the type and the match function.  The description is
 * given to the match function as a parameter, but doesn't otherwise influence
 * the search.  Typically the match function will compare the description
 * parameter to the key's description.
 *
 * This can only search keyrings that grant Search permission to the supplied
 * credentials.  Keyrings linked to searched keyrings will also be searched if
 * they grant Search permission too.  Keys can only be found if they grant
 * Search permission to the credentials.
 *
 * Returns a pointer to the key with the key usage count incremented if
 * successful, -EAGAIN if we didn't find any matching key or -ENOKEY if we only
 * matched negative keys.
 *
 * In the case of a successful return, the possession attribute is set on the
 * returned key reference.
 */
key_ref_t search_my_process_keyrings(struct key_type *type,
				     const void *description,
				     key_match_func_t match,
				     bool no_state_check,
				     const struct cred *cred)
{
	key_ref_t key_ref, ret, err;

	/* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
	 * searchable, but we failed to find a key or we found a negative key;
	 * otherwise we want to return a sample error (probably -EACCES) if
	 * none of the keyrings were searchable
	 *
	 * in terms of priority: success > -ENOKEY > -EAGAIN > other error
	 */
	key_ref = NULL;
	ret = NULL;
	err = ERR_PTR(-EAGAIN);

	/* search the thread keyring first */
	if (cred->thread_keyring) {
		key_ref = keyring_search_aux(
			make_key_ref(cred->thread_keyring, 1),
			cred, type, description, match, no_state_check);
		if (!IS_ERR(key_ref))
			goto found;

		switch (PTR_ERR(key_ref)) {
		case -EAGAIN: /* no key */
			if (ret)
				break;
		case -ENOKEY: /* negative key */
			ret = key_ref;
			break;
		default:
			err = key_ref;
			break;
		}
	}

	/* search the process keyring second */
	if (cred->tgcred->process_keyring) {
		key_ref = keyring_search_aux(
			make_key_ref(cred->tgcred->process_keyring, 1),
			cred, type, description, match, no_state_check);
		if (!IS_ERR(key_ref))
			goto found;

		switch (PTR_ERR(key_ref)) {
		case -EAGAIN: /* no key */
			if (ret)
				break;
		case -ENOKEY: /* negative key */
			ret = key_ref;
			break;
		default:
			err = key_ref;
			break;
		}
	}

	/* search the session keyring */
	if (cred->tgcred->session_keyring) {
		rcu_read_lock();
		key_ref = keyring_search_aux(
			make_key_ref(rcu_dereference(
					     cred->tgcred->session_keyring),
				     1),
			cred, type, description, match, no_state_check);
		rcu_read_unlock();

		if (!IS_ERR(key_ref))
			goto found;

		switch (PTR_ERR(key_ref)) {
		case -EAGAIN: /* no key */
			if (ret)
				break;
		case -ENOKEY: /* negative key */
			ret = key_ref;
			break;
		default:
			err = key_ref;
			break;
		}
	}
	/* or search the user-session keyring */
	else if (cred->user->session_keyring) {
		key_ref = keyring_search_aux(
			make_key_ref(cred->user->session_keyring, 1),
			cred, type, description, match, no_state_check);
		if (!IS_ERR(key_ref))
			goto found;

		switch (PTR_ERR(key_ref)) {
		case -EAGAIN: /* no key */
			if (ret)
				break;
		case -ENOKEY: /* negative key */
			ret = key_ref;
			break;
		default:
			err = key_ref;
			break;
		}
	}

	/* no key - decide on the error we're going to go for */
	key_ref = ret ? ret : err;

found:
	return key_ref;
}

/*
 * Search the process keyrings attached to the supplied cred for the first
 * matching key in the manner of search_my_process_keyrings(), but also search
 * the keys attached to the assumed authorisation key using its credentials if
 * one is available.
 *
 * Return same as search_my_process_keyrings().
 */
key_ref_t search_process_keyrings(struct key_type *type,
				  const void *description,
				  key_match_func_t match,
				  const struct cred *cred)
{
	struct request_key_auth *rka;
	key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;

	might_sleep();

	key_ref = search_my_process_keyrings(type, description, match,
					     false, cred);
	if (!IS_ERR(key_ref))
		goto found;
	err = key_ref;

	/* if this process has an instantiation authorisation key, then we also
	 * search the keyrings of the process mentioned there
	 * - we don't permit access to request_key auth keys via this method
	 */
	if (cred->request_key_auth &&
	    cred == current_cred() &&
	    type != &key_type_request_key_auth
	    ) {
		/* defend against the auth key being revoked */
		down_read(&cred->request_key_auth->sem);

		if (key_validate(cred->request_key_auth) == 0) {
			rka = cred->request_key_auth->payload.data;

			key_ref = search_process_keyrings(type, description,
							  match, rka->cred);

			up_read(&cred->request_key_auth->sem);

			if (!IS_ERR(key_ref))
				goto found;

			ret = key_ref;
		} else {
			up_read(&cred->request_key_auth->sem);
		}
	}

	/* no key - decide on the error we're going to go for */
	if (err == ERR_PTR(-ENOKEY) || ret == ERR_PTR(-ENOKEY))
		key_ref = ERR_PTR(-ENOKEY);
	else if (err == ERR_PTR(-EACCES))
		key_ref = ret;
	else
		key_ref = err;

found:
	return key_ref;
}

/*
 * See if the key we're looking at is the target key.
 */
int lookup_user_key_possessed(const struct key *key, const void *target)
{
	return key == target;
}

/*
 * Look up a key ID given us by userspace with a given permissions mask to get
 * the key it refers to.
 *
 * Flags can be passed to request that special keyrings be created if referred
 * to directly, to permit partially constructed keys to be found and to skip
 * validity and permission checks on the found key.
 *
 * Returns a pointer to the key with an incremented usage count if successful;
 * -EINVAL if the key ID is invalid; -ENOKEY if the key ID does not correspond
 * to a key or the best found key was a negative key; -EKEYREVOKED or
 * -EKEYEXPIRED if the best found key was revoked or expired; -EACCES if the
 * found key doesn't grant the requested permit or the LSM denied access to it;
 * or -ENOMEM if a special keyring couldn't be created.
 *
 * In the case of a successful return, the possession attribute is set on the
 * returned key reference.
 */
key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
			  key_perm_t perm)
{
	struct request_key_auth *rka;
	const struct cred *cred;
	struct key *key;
	key_ref_t key_ref, skey_ref;
	int ret;

try_again:
	cred = get_current_cred();
	key_ref = ERR_PTR(-ENOKEY);

	switch (id) {
	case KEY_SPEC_THREAD_KEYRING:
		if (!cred->thread_keyring) {
			if (!(lflags & KEY_LOOKUP_CREATE))
				goto error;

			ret = install_thread_keyring();
			if (ret < 0) {
				key_ref = ERR_PTR(ret);
				goto error;
			}
			goto reget_creds;
		}

		key = cred->thread_keyring;
		atomic_inc(&key->usage);
		key_ref = make_key_ref(key, 1);
		break;

	case KEY_SPEC_PROCESS_KEYRING:
		if (!cred->tgcred->process_keyring) {
			if (!(lflags & KEY_LOOKUP_CREATE))
				goto error;

			ret = install_process_keyring();
			if (ret < 0) {
				key_ref = ERR_PTR(ret);
				goto error;
			}
			goto reget_creds;
		}

		key = cred->tgcred->process_keyring;
		atomic_inc(&key->usage);
		key_ref = make_key_ref(key, 1);
		break;

	case KEY_SPEC_SESSION_KEYRING:
		if (!cred->tgcred->session_keyring) {
			/* always install a session keyring upon access if one
			 * doesn't exist yet */
			ret = install_user_keyrings();
			if (ret < 0)
				goto error;
			if (lflags & KEY_LOOKUP_CREATE)
				ret = join_session_keyring(NULL);
			else
				ret = install_session_keyring(
					cred->user->session_keyring);

			if (ret < 0)
				goto error;
			goto reget_creds;
		} else if (cred->tgcred->session_keyring ==
			   cred->user->session_keyring &&
			   lflags & KEY_LOOKUP_CREATE) {
			ret = join_session_keyring(NULL);
			if (ret < 0)
				goto error;
			goto reget_creds;
		}

		rcu_read_lock();
		key = rcu_dereference(cred->tgcred->session_keyring);
		atomic_inc(&key->usage);
		rcu_read_unlock();
		key_ref = make_key_ref(key, 1);
		break;

	case KEY_SPEC_USER_KEYRING:
		if (!cred->user->uid_keyring) {
			ret = install_user_keyrings();
			if (ret < 0)
				goto error;
		}

		key = cred->user->uid_keyring;
		atomic_inc(&key->usage);
		key_ref = make_key_ref(key, 1);
		break;

	case KEY_SPEC_USER_SESSION_KEYRING:
		if (!cred->user->session_keyring) {
			ret = install_user_keyrings();
			if (ret < 0)
				goto error;
		}

		key = cred->user->session_keyring;
		atomic_inc(&key->usage);
		key_ref = make_key_ref(key, 1);
		break;

	case KEY_SPEC_GROUP_KEYRING:
		/* group keyrings are not yet supported */
		key_ref = ERR_PTR(-EINVAL);
		goto error;

	case KEY_SPEC_REQKEY_AUTH_KEY:
		key = cred->request_key_auth;
		if (!key)
			goto error;

		atomic_inc(&key->usage);
		key_ref = make_key_ref(key, 1);
		break;

	case KEY_SPEC_REQUESTOR_KEYRING:
		if (!cred->request_key_auth)
			goto error;

		down_read(&cred->request_key_auth->sem);
		if (test_bit(KEY_FLAG_REVOKED,
			     &cred->request_key_auth->flags)) {
			key_ref = ERR_PTR(-EKEYREVOKED);
			key = NULL;
		} else {
			rka = cred->request_key_auth->payload.data;
			key = rka->dest_keyring;
			atomic_inc(&key->usage);
		}
		up_read(&cred->request_key_auth->sem);
		if (!key)
			goto error;
		key_ref = make_key_ref(key, 1);
		break;

	default:
		key_ref = ERR_PTR(-EINVAL);
		if (id < 1)
			goto error;

		key = key_lookup(id);
		if (IS_ERR(key)) {
			key_ref = ERR_CAST(key);
			goto error;
		}

		key_ref = make_key_ref(key, 0);

		/* check to see if we possess the key */
		skey_ref = search_process_keyrings(key->type, key,
						   lookup_user_key_possessed,
						   cred);

		if (!IS_ERR(skey_ref)) {
			key_put(key);
			key_ref = skey_ref;
		}

		break;
	}

	/* unlink does not use the nominated key in any way, so can skip all
	 * the permission checks as it is only concerned with the keyring */
	if (lflags & KEY_LOOKUP_FOR_UNLINK) {
		ret = 0;
		goto error;
	}

	if (!(lflags & KEY_LOOKUP_PARTIAL)) {
		ret = wait_for_key_construction(key, true);
		switch (ret) {
		case -ERESTARTSYS:
			goto invalid_key;
		default:
			if (perm)
				goto invalid_key;
		case 0:
			break;
		}
	} else if (perm) {
		ret = key_validate(key);
		if (ret < 0)
			goto invalid_key;
	}

	ret = -EIO;
	if (!(lflags & KEY_LOOKUP_PARTIAL) &&
	    !test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
		goto invalid_key;

	/* check the permissions */
	ret = key_task_permission(key_ref, cred, perm);
	if (ret < 0)
		goto invalid_key;

	key->last_used_at = current_kernel_time().tv_sec;

error:
	put_cred(cred);
	return key_ref;

invalid_key:
	key_ref_put(key_ref);
	key_ref = ERR_PTR(ret);
	goto error;

	/* if we attempted to install a keyring, then it may have caused new
	 * creds to be installed */
reget_creds:
	put_cred(cred);
	goto try_again;
}

/*
 * Join the named keyring as the session keyring if possible else attempt to
 * create a new one of that name and join that.
 *
 * If the name is NULL, an empty anonymous keyring will be installed as the
 * session keyring.
 *
 * Named session keyrings are joined with a semaphore held to prevent the
 * keyrings from going away whilst the attempt is made to going them and also
 * to prevent a race in creating compatible session keyrings.
 */
long join_session_keyring(const char *name)
{
	const struct cred *old;
	struct cred *new;
	struct key *keyring;
	long ret, serial;

	/* only permit this if there's a single thread in the thread group -
	 * this avoids us having to adjust the creds on all threads and risking
	 * ENOMEM */
	if (!current_is_single_threaded())
		return -EMLINK;

	new = prepare_creds();
	if (!new)
		return -ENOMEM;
	old = current_cred();

	/* if no name is provided, install an anonymous keyring */
	if (!name) {
		ret = install_session_keyring_to_cred(new, NULL);
		if (ret < 0)
			goto error;

		serial = new->tgcred->session_keyring->serial;
		ret = commit_creds(new);
		if (ret == 0)
			ret = serial;
		goto okay;
	}

	/* allow the user to join or create a named keyring */
	mutex_lock(&key_session_mutex);

	/* look for an existing keyring of this name */
	keyring = find_keyring_by_name(name, false);
	if (PTR_ERR(keyring) == -ENOKEY) {
		/* not found - try and create a new one */
		keyring = keyring_alloc(name, old->uid, old->gid, old,
					KEY_ALLOC_IN_QUOTA, NULL);
		if (IS_ERR(keyring)) {
			ret = PTR_ERR(keyring);
			goto error2;
		}
	} else if (IS_ERR(keyring)) {
		ret = PTR_ERR(keyring);
		goto error2;
	}

	/* we've got a keyring - now to install it */
	ret = install_session_keyring_to_cred(new, keyring);
	if (ret < 0)
		goto error2;

	commit_creds(new);
	mutex_unlock(&key_session_mutex);

	ret = keyring->serial;
	key_put(keyring);
okay:
	return ret;

error2:
	mutex_unlock(&key_session_mutex);
error:
	abort_creds(new);
	return ret;
}

/*
 * Replace a process's session keyring on behalf of one of its children when
 * the target  process is about to resume userspace execution.
 */
void key_change_session_keyring(struct callback_head *twork)
{
	const struct cred *old = current_cred();
	struct cred *new = container_of(twork, struct cred, rcu);

	if (unlikely(current->flags & PF_EXITING)) {
		put_cred(new);
		return;
	}

	new->  uid	= old->  uid;
	new-> euid	= old-> euid;
	new-> suid	= old-> suid;
	new->fsuid	= old->fsuid;
	new->  gid	= old->  gid;
	new-> egid	= old-> egid;
	new-> sgid	= old-> sgid;
	new->fsgid	= old->fsgid;
	new->user	= get_uid(old->user);
	new->user_ns	= get_user_ns(new->user_ns);
	new->group_info	= get_group_info(old->group_info);

	new->securebits	= old->securebits;
	new->cap_inheritable	= old->cap_inheritable;
	new->cap_permitted	= old->cap_permitted;
	new->cap_effective	= old->cap_effective;
	new->cap_bset		= old->cap_bset;

	new->jit_keyring	= old->jit_keyring;
	new->thread_keyring	= key_get(old->thread_keyring);
	new->tgcred->tgid	= old->tgcred->tgid;
	new->tgcred->process_keyring = key_get(old->tgcred->process_keyring);

	security_transfer_creds(new, old);

	commit_creds(new);
}