228 lines
5.4 KiB
C
228 lines
5.4 KiB
C
/*
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* Copyright (C) 2005-2010 IBM Corporation
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*
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* Authors:
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* Mimi Zohar <zohar@us.ibm.com>
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* Kylene Hall <kjhall@us.ibm.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 2 of the License.
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*
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* File: evm_crypto.c
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* Using root's kernel master key (kmk), calculate the HMAC
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*/
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#include <linux/module.h>
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#include <linux/crypto.h>
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#include <linux/xattr.h>
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#include <keys/encrypted-type.h>
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#include <crypto/hash.h>
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#include "evm.h"
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#define EVMKEY "evm-key"
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#define MAX_KEY_SIZE 128
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static unsigned char evmkey[MAX_KEY_SIZE];
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static int evmkey_len = MAX_KEY_SIZE;
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struct crypto_shash *hmac_tfm;
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static DEFINE_MUTEX(mutex);
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static struct shash_desc *init_desc(void)
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{
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int rc;
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struct shash_desc *desc;
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if (hmac_tfm == NULL) {
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mutex_lock(&mutex);
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if (hmac_tfm)
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goto out;
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hmac_tfm = crypto_alloc_shash(evm_hmac, 0, CRYPTO_ALG_ASYNC);
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if (IS_ERR(hmac_tfm)) {
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pr_err("Can not allocate %s (reason: %ld)\n",
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evm_hmac, PTR_ERR(hmac_tfm));
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rc = PTR_ERR(hmac_tfm);
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hmac_tfm = NULL;
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mutex_unlock(&mutex);
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return ERR_PTR(rc);
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}
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rc = crypto_shash_setkey(hmac_tfm, evmkey, evmkey_len);
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if (rc) {
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crypto_free_shash(hmac_tfm);
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hmac_tfm = NULL;
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mutex_unlock(&mutex);
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return ERR_PTR(rc);
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}
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out:
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mutex_unlock(&mutex);
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}
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desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(hmac_tfm),
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GFP_KERNEL);
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if (!desc)
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return ERR_PTR(-ENOMEM);
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desc->tfm = hmac_tfm;
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desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
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rc = crypto_shash_init(desc);
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if (rc) {
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kfree(desc);
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return ERR_PTR(rc);
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}
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return desc;
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}
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/* Protect against 'cutting & pasting' security.evm xattr, include inode
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* specific info.
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*
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* (Additional directory/file metadata needs to be added for more complete
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* protection.)
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*/
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static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
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char *digest)
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{
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struct h_misc {
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unsigned long ino;
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__u32 generation;
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uid_t uid;
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gid_t gid;
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umode_t mode;
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} hmac_misc;
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memset(&hmac_misc, 0, sizeof hmac_misc);
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hmac_misc.ino = inode->i_ino;
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hmac_misc.generation = inode->i_generation;
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hmac_misc.uid = inode->i_uid;
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hmac_misc.gid = inode->i_gid;
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hmac_misc.mode = inode->i_mode;
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crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof hmac_misc);
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crypto_shash_final(desc, digest);
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}
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/*
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* Calculate the HMAC value across the set of protected security xattrs.
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*
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* Instead of retrieving the requested xattr, for performance, calculate
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* the hmac using the requested xattr value. Don't alloc/free memory for
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* each xattr, but attempt to re-use the previously allocated memory.
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*/
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int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
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const char *req_xattr_value, size_t req_xattr_value_len,
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char *digest)
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{
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struct inode *inode = dentry->d_inode;
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struct shash_desc *desc;
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char **xattrname;
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size_t xattr_size = 0;
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char *xattr_value = NULL;
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int error;
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int size;
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if (!inode->i_op || !inode->i_op->getxattr)
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return -EOPNOTSUPP;
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desc = init_desc();
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if (IS_ERR(desc))
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return PTR_ERR(desc);
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error = -ENODATA;
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for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
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if ((req_xattr_name && req_xattr_value)
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&& !strcmp(*xattrname, req_xattr_name)) {
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error = 0;
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crypto_shash_update(desc, (const u8 *)req_xattr_value,
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req_xattr_value_len);
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continue;
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}
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size = vfs_getxattr_alloc(dentry, *xattrname,
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&xattr_value, xattr_size, GFP_NOFS);
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if (size == -ENOMEM) {
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error = -ENOMEM;
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goto out;
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}
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if (size < 0)
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continue;
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error = 0;
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xattr_size = size;
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crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
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}
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hmac_add_misc(desc, inode, digest);
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out:
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kfree(xattr_value);
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kfree(desc);
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return error;
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}
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/*
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* Calculate the hmac and update security.evm xattr
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*
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* Expects to be called with i_mutex locked.
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*/
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int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
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const char *xattr_value, size_t xattr_value_len)
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{
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struct inode *inode = dentry->d_inode;
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struct evm_ima_xattr_data xattr_data;
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int rc = 0;
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rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
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xattr_value_len, xattr_data.digest);
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if (rc == 0) {
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xattr_data.type = EVM_XATTR_HMAC;
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rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
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&xattr_data,
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sizeof(xattr_data), 0);
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}
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else if (rc == -ENODATA)
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rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM);
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return rc;
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}
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int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
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char *hmac_val)
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{
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struct shash_desc *desc;
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desc = init_desc();
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if (IS_ERR(desc)) {
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printk(KERN_INFO "init_desc failed\n");
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return PTR_ERR(desc);
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}
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crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
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hmac_add_misc(desc, inode, hmac_val);
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kfree(desc);
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return 0;
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}
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/*
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* Get the key from the TPM for the SHA1-HMAC
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*/
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int evm_init_key(void)
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{
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struct key *evm_key;
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struct encrypted_key_payload *ekp;
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int rc = 0;
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evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
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if (IS_ERR(evm_key))
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return -ENOENT;
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down_read(&evm_key->sem);
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ekp = evm_key->payload.data;
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if (ekp->decrypted_datalen > MAX_KEY_SIZE) {
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rc = -EINVAL;
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goto out;
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}
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memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen);
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out:
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/* burn the original key contents */
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memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
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up_read(&evm_key->sem);
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key_put(evm_key);
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return rc;
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}
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