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428 lines
11 KiB
428 lines
11 KiB
// 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 <[email protected]> |
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* Kylene Hall <[email protected]> |
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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; |
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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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return ERR_PTR(-ENOMEM); |
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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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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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