security/keys/dh.c

/* Crypto operations using stored keys
 *
 * Copyright (c) 2016, Intel Corporation
 *
 * 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/mpi.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <keys/user-type.h>
#include "internal.h"

/*
 * Public key or shared secret generation function [RFC2631 sec 2.1.1]
 *
 * ya = g^xa mod p;
 * or
 * ZZ = yb^xa mod p;
 *
 * where xa is the local private key, ya is the local public key, g is
 * the generator, p is the prime, yb is the remote public key, and ZZ
 * is the shared secret.
 *
 * Both are the same calculation, so g or yb are the "base" and ya or
 * ZZ are the "result".
 */
static int do_dh(MPI result, MPI base, MPI xa, MPI p)
{
	return mpi_powm(result, base, xa, p);
}

static ssize_t mpi_from_key(key_serial_t keyid, size_t maxlen, MPI *mpi)
{
	struct key *key;
	key_ref_t key_ref;
	long status;
	ssize_t ret;

	key_ref = lookup_user_key(keyid, 0, KEY_NEED_READ);
	if (IS_ERR(key_ref)) {
		ret = -ENOKEY;
		goto error;
	}

	key = key_ref_to_ptr(key_ref);

	ret = -EOPNOTSUPP;
	if (key->type == &key_type_user) {
		down_read(&key->sem);
		status = key_validate(key);
		if (status == 0) {
			const struct user_key_payload *payload;

			payload = user_key_payload_locked(key);

			if (maxlen == 0) {
				*mpi = NULL;
				ret = payload->datalen;
			} else if (payload->datalen <= maxlen) {
				*mpi = mpi_read_raw_data(payload->data,
							 payload->datalen);
				if (*mpi)
					ret = payload->datalen;
			} else {
				ret = -EINVAL;
			}
		}
		up_read(&key->sem);
	}

	key_put(key);
error:
	return ret;
}

long keyctl_dh_compute(struct keyctl_dh_params __user *params,
		       char __user *buffer, size_t buflen,
		       void __user *reserved)
{
	long ret;
	MPI base, private, prime, result;
	unsigned nbytes;
	struct keyctl_dh_params pcopy;
	uint8_t *kbuf;
	ssize_t keylen;
	size_t resultlen;

	if (!params || (!buffer && buflen)) {
		ret = -EINVAL;
		goto out;
	}
	if (copy_from_user(&pcopy, params, sizeof(pcopy)) != 0) {
		ret = -EFAULT;
		goto out;
	}

	if (reserved) {
		ret = -EINVAL;
		goto out;
	}

	keylen = mpi_from_key(pcopy.prime, buflen, &prime);
	if (keylen < 0 || !prime) {
		/* buflen == 0 may be used to query the required buffer size,
		 * which is the prime key length.
		 */
		ret = keylen;
		goto out;
	}

	/* The result is never longer than the prime */
	resultlen = keylen;

	keylen = mpi_from_key(pcopy.base, SIZE_MAX, &base);
	if (keylen < 0 || !base) {
		ret = keylen;
		goto error1;
	}

	keylen = mpi_from_key(pcopy.private, SIZE_MAX, &private);
	if (keylen < 0 || !private) {
		ret = keylen;
		goto error2;
	}

	result = mpi_alloc(0);
	if (!result) {
		ret = -ENOMEM;
		goto error3;
	}

	kbuf = kmalloc(resultlen, GFP_KERNEL);
	if (!kbuf) {
		ret = -ENOMEM;
		goto error4;
	}

	ret = do_dh(result, base, private, prime);
	if (ret)
		goto error5;

	ret = mpi_read_buffer(result, kbuf, resultlen, &nbytes, NULL);
	if (ret != 0)
		goto error5;

	ret = nbytes;
	if (copy_to_user(buffer, kbuf, nbytes) != 0)
		ret = -EFAULT;

error5:
	kfree(kbuf);
error4:
	mpi_free(result);
error3:
	mpi_free(private);
error2:
	mpi_free(base);
error1:
	mpi_free(prime);
out:
	return ret;
}