request_key_auth.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* Request key authorisation token key definition.
 *
 * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * See Documentation/security/keys/request-key.rst
 */

#include <linux/sched.h>
#include <linux/err.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include "internal.h"
#include <keys/request_key_auth-type.h>

static int request_key_auth_preparse(struct key_preparsed_payload *);
static void request_key_auth_free_preparse(struct key_preparsed_payload *);
static int request_key_auth_instantiate(struct key *,
					struct key_preparsed_payload *);
static void request_key_auth_describe(const struct key *, struct seq_file *);
static void request_key_auth_revoke(struct key *);
static void request_key_auth_destroy(struct key *);
static long request_key_auth_read(const struct key *, char __user *, size_t);

/*
 * The request-key authorisation key type definition.
 */
struct key_type key_type_request_key_auth = {
	.name		= ".request_key_auth",
	.def_datalen	= sizeof(struct request_key_auth),
	.preparse	= request_key_auth_preparse,
	.free_preparse	= request_key_auth_free_preparse,
	.instantiate	= request_key_auth_instantiate,
	.describe	= request_key_auth_describe,
	.revoke		= request_key_auth_revoke,
	.destroy	= request_key_auth_destroy,
	.read		= request_key_auth_read,
};

static int request_key_auth_preparse(struct key_preparsed_payload *prep)
{
	return 0;
}

static void request_key_auth_free_preparse(struct key_preparsed_payload *prep)
{
}

/*
 * Instantiate a request-key authorisation key.
 */
static int request_key_auth_instantiate(struct key *key,
					struct key_preparsed_payload *prep)
{
	rcu_assign_keypointer(key, (struct request_key_auth *)prep->data);
	return 0;
}

/*
 * Describe an authorisation token.
 */
static void request_key_auth_describe(const struct key *key,
				      struct seq_file *m)
{
	struct request_key_auth *rka = dereference_key_rcu(key);

	if (!rka)
		return;

	seq_puts(m, "key:");
	seq_puts(m, key->description);
	if (key_is_positive(key))
		seq_printf(m, " pid:%d ci:%zu", rka->pid, rka->callout_len);
}

/*
 * Read the callout_info data (retrieves the callout information).
 * - the key's semaphore is read-locked
 */
static long request_key_auth_read(const struct key *key,
				  char __user *buffer, size_t buflen)
{
	struct request_key_auth *rka = dereference_key_locked(key);
	size_t datalen;
	long ret;

	if (!rka)
		return -EKEYREVOKED;

	datalen = rka->callout_len;
	ret = datalen;

	/* we can return the data as is */
	if (buffer && buflen > 0) {
		if (buflen > datalen)
			buflen = datalen;

		if (copy_to_user(buffer, rka->callout_info, buflen) != 0)
			ret = -EFAULT;
	}

	return ret;
}

static void free_request_key_auth(struct request_key_auth *rka)
{
	if (!rka)
		return;
	key_put(rka->target_key);
	key_put(rka->dest_keyring);
	if (rka->cred)
		put_cred(rka->cred);
	kfree(rka->callout_info);
	kfree(rka);
}

/*
 * Dispose of the request_key_auth record under RCU conditions
 */
static void request_key_auth_rcu_disposal(struct rcu_head *rcu)
{
	struct request_key_auth *rka =
		container_of(rcu, struct request_key_auth, rcu);

	free_request_key_auth(rka);
}

/*
 * Handle revocation of an authorisation token key.
 *
 * Called with the key sem write-locked.
 */
static void request_key_auth_revoke(struct key *key)
{
	struct request_key_auth *rka = dereference_key_locked(key);

	kenter("{%d}", key->serial);
	rcu_assign_keypointer(key, NULL);
	call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
}

/*
 * Destroy an instantiation authorisation token key.
 */
static void request_key_auth_destroy(struct key *key)
{
	struct request_key_auth *rka = rcu_access_pointer(key->payload.rcu_data0);

	kenter("{%d}", key->serial);
	if (rka) {
		rcu_assign_keypointer(key, NULL);
		call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
	}
}

/*
 * Create an authorisation token for /sbin/request-key or whoever to gain
 * access to the caller's security data.
 */
struct key *request_key_auth_new(struct key *target, const char *op,
				 const void *callout_info, size_t callout_len,
				 struct key *dest_keyring)
{
	struct request_key_auth *rka, *irka;
	const struct cred *cred = current_cred();
	struct key *authkey = NULL;
	char desc[20];
	int ret = -ENOMEM;

	kenter("%d,", target->serial);

	/* allocate a auth record */
	rka = kzalloc(sizeof(*rka), GFP_KERNEL);
	if (!rka)
		goto error;
	rka->callout_info = kmemdup(callout_info, callout_len, GFP_KERNEL);
	if (!rka->callout_info)
		goto error_free_rka;
	rka->callout_len = callout_len;
	strlcpy(rka->op, op, sizeof(rka->op));

	/* see if the calling process is already servicing the key request of
	 * another process */
	if (cred->request_key_auth) {
		/* it is - use that instantiation context here too */
		down_read(&cred->request_key_auth->sem);

		/* if the auth key has been revoked, then the key we're
		 * servicing is already instantiated */
		if (test_bit(KEY_FLAG_REVOKED,
			     &cred->request_key_auth->flags)) {
			up_read(&cred->request_key_auth->sem);
			ret = -EKEYREVOKED;
			goto error_free_rka;
		}

		irka = cred->request_key_auth->payload.data[0];
		rka->cred = get_cred(irka->cred);
		rka->pid = irka->pid;

		up_read(&cred->request_key_auth->sem);
	}
	else {
		/* it isn't - use this process as the context */
		rka->cred = get_cred(cred);
		rka->pid = current->pid;
	}

	rka->target_key = key_get(target);
	rka->dest_keyring = key_get(dest_keyring);

	/* allocate the auth key */
	sprintf(desc, "%x", target->serial);

	authkey = key_alloc(&key_type_request_key_auth, desc,
			    cred->fsuid, cred->fsgid, cred,
			    KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH | KEY_POS_LINK |
			    KEY_USR_VIEW, KEY_ALLOC_NOT_IN_QUOTA, NULL);
	if (IS_ERR(authkey)) {
		ret = PTR_ERR(authkey);
		goto error_free_rka;
	}

	/* construct the auth key */
	ret = key_instantiate_and_link(authkey, rka, 0, NULL, NULL);
	if (ret < 0)
		goto error_put_authkey;

	kleave(" = {%d,%d}", authkey->serial, refcount_read(&authkey->usage));
	return authkey;

error_put_authkey:
	key_put(authkey);
error_free_rka:
	free_request_key_auth(rka);
error:
	kleave("= %d", ret);
	return ERR_PTR(ret);
}

/*
 * Search the current process's keyrings for the authorisation key for
 * instantiation of a key.
 */
struct key *key_get_instantiation_authkey(key_serial_t target_id)
{
	char description[16];
	struct keyring_search_context ctx = {
		.index_key.type		= &key_type_request_key_auth,
		.index_key.description	= description,
		.cred			= current_cred(),
		.match_data.cmp		= key_default_cmp,
		.match_data.raw_data	= description,
		.match_data.lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
		.flags			= (KEYRING_SEARCH_DO_STATE_CHECK |
					   KEYRING_SEARCH_RECURSE),
	};
	struct key *authkey;
	key_ref_t authkey_ref;

	ctx.index_key.desc_len = sprintf(description, "%x", target_id);

	rcu_read_lock();
	authkey_ref = search_process_keyrings_rcu(&ctx);
	rcu_read_unlock();

	if (IS_ERR(authkey_ref)) {
		authkey = ERR_CAST(authkey_ref);
		if (authkey == ERR_PTR(-EAGAIN))
			authkey = ERR_PTR(-ENOKEY);
		goto error;
	}

	authkey = key_ref_to_ptr(authkey_ref);
	if (test_bit(KEY_FLAG_REVOKED, &authkey->flags)) {
		key_put(authkey);
		authkey = ERR_PTR(-EKEYREVOKED);
	}

error:
	return authkey;
}