1/* Crypto operations using stored keys
  2 *
  3 * Copyright (c) 2016, Intel Corporation
  4 *
  5 * This program is free software; you can redistribute it and/or
  6 * modify it under the terms of the GNU General Public License
  7 * as published by the Free Software Foundation; either version
  8 * 2 of the License, or (at your option) any later version.
  9 */
 10
 11#include <linux/mpi.h>
 12#include <linux/slab.h>
 13#include <linux/uaccess.h>
 14#include <keys/user-type.h>
 15#include "internal.h"
 16
 17/*
 18 * Public key or shared secret generation function [RFC2631 sec 2.1.1]
 19 *
 20 * ya = g^xa mod p;
 21 * or
 22 * ZZ = yb^xa mod p;
 23 *
 24 * where xa is the local private key, ya is the local public key, g is
 25 * the generator, p is the prime, yb is the remote public key, and ZZ
 26 * is the shared secret.
 27 *
 28 * Both are the same calculation, so g or yb are the "base" and ya or
 29 * ZZ are the "result".
 30 */
 31static int do_dh(MPI result, MPI base, MPI xa, MPI p)
 32{
 33	return mpi_powm(result, base, xa, p);
 34}
 35
 36static ssize_t mpi_from_key(key_serial_t keyid, size_t maxlen, MPI *mpi)
 37{
 38	struct key *key;
 39	key_ref_t key_ref;
 40	long status;
 41	ssize_t ret;
 42
 43	key_ref = lookup_user_key(keyid, 0, KEY_NEED_READ);
 44	if (IS_ERR(key_ref)) {
 45		ret = -ENOKEY;
 46		goto error;
 47	}
 48
 49	key = key_ref_to_ptr(key_ref);
 50
 51	ret = -EOPNOTSUPP;
 52	if (key->type == &key_type_user) {
 53		down_read(&key->sem);
 54		status = key_validate(key);
 55		if (status == 0) {
 56			const struct user_key_payload *payload;
 57
 58			payload = user_key_payload(key);
 59
 60			if (maxlen == 0) {
 61				*mpi = NULL;
 62				ret = payload->datalen;
 63			} else if (payload->datalen <= maxlen) {
 64				*mpi = mpi_read_raw_data(payload->data,
 65							 payload->datalen);
 66				if (*mpi)
 67					ret = payload->datalen;
 68			} else {
 69				ret = -EINVAL;
 70			}
 71		}
 72		up_read(&key->sem);
 73	}
 74
 75	key_put(key);
 76error:
 77	return ret;
 78}
 79
 80long keyctl_dh_compute(struct keyctl_dh_params __user *params,
 81		       char __user *buffer, size_t buflen,
 82		       void __user *reserved)
 83{
 84	long ret;
 85	MPI base, private, prime, result;
 86	unsigned nbytes;
 87	struct keyctl_dh_params pcopy;
 88	uint8_t *kbuf;
 89	ssize_t keylen;
 90	size_t resultlen;
 91
 92	if (!params || (!buffer && buflen)) {
 93		ret = -EINVAL;
 94		goto out;
 95	}
 96	if (copy_from_user(&pcopy, params, sizeof(pcopy)) != 0) {
 97		ret = -EFAULT;
 98		goto out;
 99	}
100
101	if (reserved) {
102		ret = -EINVAL;
103		goto out;
104	}
105
106	keylen = mpi_from_key(pcopy.prime, buflen, &prime);
107	if (keylen < 0 || !prime) {
108		/* buflen == 0 may be used to query the required buffer size,
109		 * which is the prime key length.
110		 */
111		ret = keylen;
112		goto out;
113	}
114
115	/* The result is never longer than the prime */
116	resultlen = keylen;
117
118	keylen = mpi_from_key(pcopy.base, SIZE_MAX, &base);
119	if (keylen < 0 || !base) {
120		ret = keylen;
121		goto error1;
122	}
123
124	keylen = mpi_from_key(pcopy.private, SIZE_MAX, &private);
125	if (keylen < 0 || !private) {
126		ret = keylen;
127		goto error2;
128	}
129
130	result = mpi_alloc(0);
131	if (!result) {
132		ret = -ENOMEM;
133		goto error3;
134	}
135
136	kbuf = kmalloc(resultlen, GFP_KERNEL);
137	if (!kbuf) {
138		ret = -ENOMEM;
139		goto error4;
140	}
141
142	ret = do_dh(result, base, private, prime);
143	if (ret)
144		goto error5;
145
146	ret = mpi_read_buffer(result, kbuf, resultlen, &nbytes, NULL);
147	if (ret != 0)
148		goto error5;
149
150	ret = nbytes;
151	if (copy_to_user(buffer, kbuf, nbytes) != 0)
152		ret = -EFAULT;
153
154error5:
155	kfree(kbuf);
156error4:
157	mpi_free(result);
158error3:
159	mpi_free(private);
160error2:
161	mpi_free(base);
162error1:
163	mpi_free(prime);
164out:
165	return ret;
166}