diff options
Diffstat (limited to 'security/integrity/evm/evm_crypto.c')
| -rw-r--r-- | security/integrity/evm/evm_crypto.c | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c new file mode 100644 index 00000000000..d49bb002f3d --- /dev/null +++ b/security/integrity/evm/evm_crypto.c @@ -0,0 +1,183 @@ +/* + * 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 + */ + +#include <linux/module.h> +#include <linux/crypto.h> +#include <linux/xattr.h> +#include <linux/scatterlist.h> +#include <keys/encrypted-type.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; + +static int init_desc(struct hash_desc *desc) +{ + int rc; + + desc->tfm = crypto_alloc_hash(evm_hmac, 0, CRYPTO_ALG_ASYNC); + if (IS_ERR(desc->tfm)) { + pr_info("Can not allocate %s (reason: %ld)\n", + evm_hmac, PTR_ERR(desc->tfm)); + rc = PTR_ERR(desc->tfm); + return rc; + } + desc->flags = 0; + rc = crypto_hash_setkey(desc->tfm, evmkey, evmkey_len); + if (rc) + goto out; + rc = crypto_hash_init(desc); +out: + if (rc) + crypto_free_hash(desc->tfm); + return rc; +} + +/* 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 hash_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; + struct scatterlist sg[1]; + + memset(&hmac_misc, 0, sizeof hmac_misc); + hmac_misc.ino = inode->i_ino; + hmac_misc.generation = inode->i_generation; + hmac_misc.uid = inode->i_uid; + hmac_misc.gid = inode->i_gid; + hmac_misc.mode = inode->i_mode; + sg_init_one(sg, &hmac_misc, sizeof hmac_misc); + crypto_hash_update(desc, sg, sizeof hmac_misc); + crypto_hash_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. + */ +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) +{ + struct inode *inode = dentry->d_inode; + struct hash_desc desc; + struct scatterlist sg[1]; + char **xattrname; + size_t xattr_size = 0; + char *xattr_value = NULL; + int error; + int size; + + if (!inode->i_op || !inode->i_op->getxattr) + return -EOPNOTSUPP; + error = init_desc(&desc); + if (error) + return error; + + error = -ENODATA; + for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) { + if ((req_xattr_name && req_xattr_value) + && !strcmp(*xattrname, req_xattr_name)) { + error = 0; + sg_init_one(sg, req_xattr_value, req_xattr_value_len); + crypto_hash_update(&desc, sg, 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; + sg_init_one(sg, xattr_value, xattr_size); + crypto_hash_update(&desc, sg, xattr_size); + } + hmac_add_misc(&desc, inode, digest); + kfree(xattr_value); +out: + crypto_free_hash(desc.tfm); + return error; +} + +/* + * 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 = dentry->d_inode; + u8 hmac[SHA1_DIGEST_SIZE]; + int rc = 0; + + rc = evm_calc_hmac(dentry, xattr_name, xattr_value, + xattr_value_len, hmac); + if (rc == 0) + rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM, + hmac, SHA1_DIGEST_SIZE, 0); + else if (rc == -ENODATA) + rc = inode->i_op->removexattr(dentry, XATTR_NAME_EVM); + return rc; +} + +/* + * 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 = 0; + + 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; + if (ekp->decrypted_datalen > MAX_KEY_SIZE) { + rc = -EINVAL; + goto out; + } + memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen); +out: + /* burn the original key contents */ + memset(ekp->decrypted_data, 0, ekp->decrypted_datalen); + up_read(&evm_key->sem); + key_put(evm_key); + return rc; +} |