432 строки
11 KiB
C
432 строки
11 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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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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* 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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#define pr_fmt(fmt) "EVM: "fmt
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#include <linux/export.h>
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#include <linux/crypto.h>
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#include <linux/xattr.h>
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#include <linux/evm.h>
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#include <keys/encrypted-type.h>
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#include <crypto/hash.h>
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#include <crypto/hash_info.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 const int evmkey_len = MAX_KEY_SIZE;
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static struct crypto_shash *hmac_tfm;
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static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
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static DEFINE_MUTEX(mutex);
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#define EVM_SET_KEY_BUSY 0
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static unsigned long evm_set_key_flags;
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static const char evm_hmac[] = "hmac(sha1)";
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/**
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* evm_set_key() - set EVM HMAC key from the kernel
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* @key: pointer to a buffer with the key data
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* @size: length of the key data
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*
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* This function allows setting the EVM HMAC key from the kernel
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* without using the "encrypted" key subsystem keys. It can be used
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* by the crypto HW kernel module which has its own way of managing
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* keys.
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*
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* key length should be between 32 and 128 bytes long
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*/
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int evm_set_key(void *key, size_t keylen)
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{
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int rc;
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rc = -EBUSY;
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if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
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goto busy;
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rc = -EINVAL;
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if (keylen > MAX_KEY_SIZE)
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goto inval;
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memcpy(evmkey, key, keylen);
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evm_initialized |= EVM_INIT_HMAC;
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pr_info("key initialized\n");
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return 0;
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inval:
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clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
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busy:
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pr_err("key initialization failed\n");
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return rc;
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}
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EXPORT_SYMBOL_GPL(evm_set_key);
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static struct shash_desc *init_desc(char type, uint8_t hash_algo)
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{
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long rc;
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const char *algo;
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struct crypto_shash **tfm, *tmp_tfm = NULL;
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struct shash_desc *desc;
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if (type == EVM_XATTR_HMAC) {
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if (!(evm_initialized & EVM_INIT_HMAC)) {
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pr_err_once("HMAC key is not set\n");
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return ERR_PTR(-ENOKEY);
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}
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tfm = &hmac_tfm;
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algo = evm_hmac;
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} else {
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if (hash_algo >= HASH_ALGO__LAST)
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return ERR_PTR(-EINVAL);
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tfm = &evm_tfm[hash_algo];
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algo = hash_algo_name[hash_algo];
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}
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if (*tfm)
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goto alloc;
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mutex_lock(&mutex);
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if (*tfm)
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goto unlock;
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tmp_tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
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if (IS_ERR(tmp_tfm)) {
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pr_err("Can not allocate %s (reason: %ld)\n", algo,
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PTR_ERR(tmp_tfm));
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mutex_unlock(&mutex);
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return ERR_CAST(tmp_tfm);
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}
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if (type == EVM_XATTR_HMAC) {
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rc = crypto_shash_setkey(tmp_tfm, evmkey, evmkey_len);
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if (rc) {
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crypto_free_shash(tmp_tfm);
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mutex_unlock(&mutex);
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return ERR_PTR(rc);
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}
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}
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*tfm = tmp_tfm;
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unlock:
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mutex_unlock(&mutex);
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alloc:
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desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
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GFP_KERNEL);
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if (!desc) {
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crypto_free_shash(tmp_tfm);
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return ERR_PTR(-ENOMEM);
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}
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desc->tfm = *tfm;
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rc = crypto_shash_init(desc);
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if (rc) {
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crypto_free_shash(tmp_tfm);
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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 type, 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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/* Don't include the inode or generation number in portable
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* signatures
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*/
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if (type != EVM_XATTR_PORTABLE_DIGSIG) {
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hmac_misc.ino = inode->i_ino;
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hmac_misc.generation = inode->i_generation;
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}
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/* The hmac uid and gid must be encoded in the initial user
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* namespace (not the filesystems user namespace) as encoding
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* them in the filesystems user namespace allows an attack
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* where first they are written in an unprivileged fuse mount
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* of a filesystem and then the system is tricked to mount the
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* filesystem for real on next boot and trust it because
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* everything is signed.
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*/
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hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
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hmac_misc.gid = from_kgid(&init_user_ns, 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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if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
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type != EVM_XATTR_PORTABLE_DIGSIG)
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crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
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crypto_shash_final(desc, digest);
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pr_debug("hmac_misc: (%zu) [%*phN]\n", sizeof(struct h_misc),
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(int)sizeof(struct h_misc), &hmac_misc);
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}
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/*
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* Dump large security xattr values as a continuous ascii hexademical string.
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* (pr_debug is limited to 64 bytes.)
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*/
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static void dump_security_xattr(const char *prefix, const void *src,
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size_t count)
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{
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#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
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char *asciihex, *p;
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p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL);
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if (!asciihex)
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return;
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p = bin2hex(p, src, count);
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*p = 0;
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pr_debug("%s: (%zu) %.*s\n", prefix, count, (int)count * 2, asciihex);
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kfree(asciihex);
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#endif
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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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static int evm_calc_hmac_or_hash(struct dentry *dentry,
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const char *req_xattr_name,
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const char *req_xattr_value,
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size_t req_xattr_value_len,
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uint8_t type, struct evm_digest *data)
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{
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struct inode *inode = d_backing_inode(dentry);
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struct xattr_list *xattr;
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struct shash_desc *desc;
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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, user_space_size;
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bool ima_present = false;
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if (!(inode->i_opflags & IOP_XATTR) ||
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inode->i_sb->s_user_ns != &init_user_ns)
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return -EOPNOTSUPP;
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desc = init_desc(type, data->hdr.algo);
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if (IS_ERR(desc))
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return PTR_ERR(desc);
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data->hdr.length = crypto_shash_digestsize(desc->tfm);
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error = -ENODATA;
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list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
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bool is_ima = false;
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if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
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is_ima = true;
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/*
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* Skip non-enabled xattrs for locally calculated
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* signatures/HMACs.
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*/
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if (type != EVM_XATTR_PORTABLE_DIGSIG && !xattr->enabled)
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continue;
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if ((req_xattr_name && req_xattr_value)
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&& !strcmp(xattr->name, 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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if (is_ima)
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ima_present = true;
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if (req_xattr_value_len < 64)
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pr_debug("%s: (%zu) [%*phN]\n", req_xattr_name,
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req_xattr_value_len,
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(int)req_xattr_value_len,
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req_xattr_value);
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else
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dump_security_xattr(req_xattr_name,
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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(&init_user_ns, dentry, xattr->name,
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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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user_space_size = vfs_getxattr(&init_user_ns, dentry,
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xattr->name, NULL, 0);
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if (user_space_size != size)
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pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n",
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dentry->d_name.name, xattr->name, size,
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user_space_size);
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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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if (is_ima)
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ima_present = true;
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if (xattr_size < 64)
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pr_debug("%s: (%zu) [%*phN]", xattr->name, xattr_size,
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(int)xattr_size, xattr_value);
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else
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dump_security_xattr(xattr->name, xattr_value,
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xattr_size);
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}
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hmac_add_misc(desc, inode, type, data->digest);
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/* Portable EVM signatures must include an IMA hash */
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if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
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error = -EPERM;
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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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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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struct evm_digest *data)
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{
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return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
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req_xattr_value_len, EVM_XATTR_HMAC, data);
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}
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int evm_calc_hash(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 type, struct evm_digest *data)
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{
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return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
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req_xattr_value_len, type, data);
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}
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static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
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{
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const struct evm_ima_xattr_data *xattr_data = NULL;
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struct integrity_iint_cache *iint;
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int rc = 0;
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iint = integrity_iint_find(inode);
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if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
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return 1;
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/* Do this the hard way */
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rc = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_EVM,
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(char **)&xattr_data, 0, GFP_NOFS);
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if (rc <= 0) {
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if (rc == -ENODATA)
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return 0;
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return rc;
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}
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if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG)
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rc = 1;
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else
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rc = 0;
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kfree(xattr_data);
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return rc;
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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 = d_backing_inode(dentry);
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struct evm_digest data;
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int rc = 0;
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/*
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* Don't permit any transformation of the EVM xattr if the signature
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* is of an immutable type
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*/
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rc = evm_is_immutable(dentry, inode);
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if (rc < 0)
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return rc;
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if (rc)
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return -EPERM;
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data.hdr.algo = HASH_ALGO_SHA1;
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rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
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xattr_value_len, &data);
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if (rc == 0) {
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data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
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rc = __vfs_setxattr_noperm(&init_user_ns, dentry,
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XATTR_NAME_EVM,
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&data.hdr.xattr.data[1],
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SHA1_DIGEST_SIZE + 1, 0);
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} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
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rc = __vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_EVM);
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}
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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(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
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if (IS_ERR(desc)) {
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pr_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, EVM_XATTR_HMAC, 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;
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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[0];
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rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
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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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