/*
 * Copyright (C) 2005-2010 IBM Corporation
 *
 * Authors:
 * Mimi Zohar <zohar@us.ibm.com>
 * Kylene Hall <kjhall@us.ibm.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, version 2 of the License.
 *
 * File: evm_crypto.c
 *       Using root's kernel master key (kmk), calculate the HMAC
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/crypto.h>
#include <linux/xattr.h>
#include <linux/evm.h>
#include <keys/encrypted-type.h>
#include <crypto/hash.h>
#include "evm.h"

#define EVMKEY "evm-key"
#define MAX_KEY_SIZE 128
static unsigned char evmkey[MAX_KEY_SIZE];
static int evmkey_len = MAX_KEY_SIZE;

struct crypto_shash *hmac_tfm;
struct crypto_shash *hash_tfm;

static DEFINE_MUTEX(mutex);

#define EVM_SET_KEY_BUSY 0

static unsigned long evm_set_key_flags;

/**
 * evm_set_key() - set EVM HMAC key from the kernel
 * @key: pointer to a buffer with the key data
 * @size: length of the key data
 *
 * This function allows setting the EVM HMAC key from the kernel
 * without using the "encrypted" key subsystem keys. It can be used
 * by the crypto HW kernel module which has its own way of managing
 * keys.
 *
 * key length should be between 32 and 128 bytes long
 */
int evm_set_key(void *key, size_t keylen)
{
        int rc;

        rc = -EBUSY;
        if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
                goto busy;
        rc = -EINVAL;
        if (keylen > MAX_KEY_SIZE)
                goto inval;
        memcpy(evmkey, key, keylen);
        evm_initialized |= EVM_INIT_HMAC;
        pr_info("key initialized\n");
        return 0;
inval:
        clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
busy:
        pr_err("key initialization failed\n");
        return rc;
}
EXPORT_SYMBOL_GPL(evm_set_key);

static struct shash_desc *init_desc(char type)
{
        long rc;
        char *algo;
        struct crypto_shash **tfm;
        struct shash_desc *desc;

        if (type == EVM_XATTR_HMAC) {
                if (!(evm_initialized & EVM_INIT_HMAC)) {
                        pr_err("HMAC key is not set\n");
                        return ERR_PTR(-ENOKEY);
                }
                tfm = &hmac_tfm;
                algo = evm_hmac;
        } else {
                tfm = &hash_tfm;
                algo = evm_hash;
        }

        if (*tfm == NULL) {
                mutex_lock(&mutex);
                if (*tfm)
                        goto out;
                *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
                if (IS_ERR(*tfm)) {
                        rc = PTR_ERR(*tfm);
                        pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
                        *tfm = NULL;
                        mutex_unlock(&mutex);
                        return ERR_PTR(rc);
                }
                if (type == EVM_XATTR_HMAC) {
                        rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
                        if (rc) {
                                crypto_free_shash(*tfm);
                                *tfm = NULL;
                                mutex_unlock(&mutex);
                                return ERR_PTR(rc);
                        }
                }
out:
                mutex_unlock(&mutex);
        }

        desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
                        GFP_KERNEL);
        if (!desc)
                return ERR_PTR(-ENOMEM);

        desc->tfm = *tfm;
        desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

        rc = crypto_shash_init(desc);
        if (rc) {
                kfree(desc);
                return ERR_PTR(rc);
        }
        return desc;
}

/* Protect against 'cutting & pasting' security.evm xattr, include inode
 * specific info.
 *
 * (Additional directory/file metadata needs to be added for more complete
 * protection.)
 */
static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
                          char *digest)
{
        struct h_misc {
                unsigned long ino;
                __u32 generation;
                uid_t uid;
                gid_t gid;
                umode_t mode;
        } hmac_misc;

        memset(&hmac_misc, 0, sizeof(hmac_misc));
        hmac_misc.ino = inode->i_ino;
        hmac_misc.generation = inode->i_generation;
        hmac_misc.uid = from_kuid(inode->i_sb->s_user_ns, inode->i_uid);
        hmac_misc.gid = from_kgid(inode->i_sb->s_user_ns, inode->i_gid);
        hmac_misc.mode = inode->i_mode;
        crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
        if (evm_hmac_attrs & EVM_ATTR_FSUUID)
                crypto_shash_update(desc, inode->i_sb->s_uuid,
                                    sizeof(inode->i_sb->s_uuid));
        crypto_shash_final(desc, digest);
}

/*
 * Calculate the HMAC value across the set of protected security xattrs.
 *
 * Instead of retrieving the requested xattr, for performance, calculate
 * the hmac using the requested xattr value. Don't alloc/free memory for
 * each xattr, but attempt to re-use the previously allocated memory.
 */
static int evm_calc_hmac_or_hash(struct dentry *dentry,
                                const char *req_xattr_name,
                                const char *req_xattr_value,
                                size_t req_xattr_value_len,
                                char type, char *digest)
{
        struct inode *inode = d_backing_inode(dentry);
        struct shash_desc *desc;
        char **xattrname;
        size_t xattr_size = 0;
        char *xattr_value = NULL;
        int error;
        int size;

        if (!(inode->i_opflags & IOP_XATTR))
                return -EOPNOTSUPP;

        desc = init_desc(type);
        if (IS_ERR(desc))
                return PTR_ERR(desc);

        error = -ENODATA;
        for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
                if ((req_xattr_name && req_xattr_value)
                    && !strcmp(*xattrname, req_xattr_name)) {
                        error = 0;
                        crypto_shash_update(desc, (const u8 *)req_xattr_value,
                                             req_xattr_value_len);
                        continue;
                }
                size = vfs_getxattr_alloc(dentry, *xattrname,
                                          &xattr_value, xattr_size, GFP_NOFS);
                if (size == -ENOMEM) {
                        error = -ENOMEM;
                        goto out;
                }
                if (size < 0)
                        continue;

                error = 0;
                xattr_size = size;
                crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
        }
        hmac_add_misc(desc, inode, digest);

out:
        kfree(xattr_value);
        kfree(desc);
        return error;
}

int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
                  const char *req_xattr_value, size_t req_xattr_value_len,
                  char *digest)
{
        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
                                req_xattr_value_len, EVM_XATTR_HMAC, digest);
}

int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
                  const char *req_xattr_value, size_t req_xattr_value_len,
                  char *digest)
{
        return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
                                req_xattr_value_len, IMA_XATTR_DIGEST, digest);
}

/*
 * Calculate the hmac and update security.evm xattr
 *
 * Expects to be called with i_mutex locked.
 */
int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
                        const char *xattr_value, size_t xattr_value_len)
{
        struct inode *inode = d_backing_inode(dentry);
        struct evm_ima_xattr_data xattr_data;
        int rc = 0;

        rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
                           xattr_value_len, xattr_data.digest);
        if (rc == 0) {
                xattr_data.type = EVM_XATTR_HMAC;
                rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
                                           &xattr_data,
                                           sizeof(xattr_data), 0);
        } else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
                rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
        }
        return rc;
}

int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
                  char *hmac_val)
{
        struct shash_desc *desc;

        desc = init_desc(EVM_XATTR_HMAC);
        if (IS_ERR(desc)) {
                pr_info("init_desc failed\n");
                return PTR_ERR(desc);
        }

        crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
        hmac_add_misc(desc, inode, hmac_val);
        kfree(desc);
        return 0;
}

/*
 * Get the key from the TPM for the SHA1-HMAC
 */
int evm_init_key(void)
{
        struct key *evm_key;
        struct encrypted_key_payload *ekp;
        int rc;

        evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
        if (IS_ERR(evm_key))
                return -ENOENT;

        down_read(&evm_key->sem);
        ekp = evm_key->payload.data[0];

        rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);

        /* burn the original key contents */
        memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
        up_read(&evm_key->sem);
        key_put(evm_key);
        return rc;
}