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![Eric Biggers](/assets/img/avatar_default.png)
With the new (in 4.9) option to use a virtually-mapped stack (CONFIG_VMAP_STACK), stack buffers cannot be used as input/output for the scatterlist crypto API because they may not be directly mappable to struct page. get_crypt_info() was using a stack buffer to hold the output from the encryption operation used to derive the per-file key. Fix it by using a heap buffer. This bug could most easily be observed in a CONFIG_DEBUG_SG kernel because this allowed the BUG in sg_set_buf() to be triggered. Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
333 lines
8.5 KiB
C
333 lines
8.5 KiB
C
/*
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* key management facility for FS encryption support.
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*
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* Copyright (C) 2015, Google, Inc.
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*
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* This contains encryption key functions.
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*
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* Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
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*/
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#include <keys/user-type.h>
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#include <linux/scatterlist.h>
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#include <linux/fscrypto.h>
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static void derive_crypt_complete(struct crypto_async_request *req, int rc)
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{
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struct fscrypt_completion_result *ecr = req->data;
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if (rc == -EINPROGRESS)
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return;
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ecr->res = rc;
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complete(&ecr->completion);
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}
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/**
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* derive_key_aes() - Derive a key using AES-128-ECB
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* @deriving_key: Encryption key used for derivation.
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* @source_key: Source key to which to apply derivation.
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* @derived_key: Derived key.
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*
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* Return: Zero on success; non-zero otherwise.
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*/
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static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
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u8 source_key[FS_AES_256_XTS_KEY_SIZE],
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u8 derived_key[FS_AES_256_XTS_KEY_SIZE])
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{
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int res = 0;
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struct skcipher_request *req = NULL;
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DECLARE_FS_COMPLETION_RESULT(ecr);
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struct scatterlist src_sg, dst_sg;
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struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
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if (IS_ERR(tfm)) {
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res = PTR_ERR(tfm);
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tfm = NULL;
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goto out;
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}
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crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
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req = skcipher_request_alloc(tfm, GFP_NOFS);
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if (!req) {
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res = -ENOMEM;
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goto out;
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}
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skcipher_request_set_callback(req,
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CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
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derive_crypt_complete, &ecr);
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res = crypto_skcipher_setkey(tfm, deriving_key,
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FS_AES_128_ECB_KEY_SIZE);
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if (res < 0)
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goto out;
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sg_init_one(&src_sg, source_key, FS_AES_256_XTS_KEY_SIZE);
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sg_init_one(&dst_sg, derived_key, FS_AES_256_XTS_KEY_SIZE);
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skcipher_request_set_crypt(req, &src_sg, &dst_sg,
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FS_AES_256_XTS_KEY_SIZE, NULL);
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res = crypto_skcipher_encrypt(req);
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if (res == -EINPROGRESS || res == -EBUSY) {
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wait_for_completion(&ecr.completion);
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res = ecr.res;
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}
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out:
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skcipher_request_free(req);
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crypto_free_skcipher(tfm);
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return res;
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}
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static int validate_user_key(struct fscrypt_info *crypt_info,
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struct fscrypt_context *ctx, u8 *raw_key,
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u8 *prefix, int prefix_size)
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{
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u8 *full_key_descriptor;
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struct key *keyring_key;
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struct fscrypt_key *master_key;
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const struct user_key_payload *ukp;
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int full_key_len = prefix_size + (FS_KEY_DESCRIPTOR_SIZE * 2) + 1;
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int res;
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full_key_descriptor = kmalloc(full_key_len, GFP_NOFS);
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if (!full_key_descriptor)
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return -ENOMEM;
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memcpy(full_key_descriptor, prefix, prefix_size);
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sprintf(full_key_descriptor + prefix_size,
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"%*phN", FS_KEY_DESCRIPTOR_SIZE,
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ctx->master_key_descriptor);
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full_key_descriptor[full_key_len - 1] = '\0';
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keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
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kfree(full_key_descriptor);
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if (IS_ERR(keyring_key))
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return PTR_ERR(keyring_key);
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if (keyring_key->type != &key_type_logon) {
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printk_once(KERN_WARNING
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"%s: key type must be logon\n", __func__);
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res = -ENOKEY;
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goto out;
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}
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down_read(&keyring_key->sem);
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ukp = user_key_payload(keyring_key);
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if (ukp->datalen != sizeof(struct fscrypt_key)) {
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res = -EINVAL;
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up_read(&keyring_key->sem);
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goto out;
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}
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master_key = (struct fscrypt_key *)ukp->data;
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BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
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if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
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printk_once(KERN_WARNING
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"%s: key size incorrect: %d\n",
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__func__, master_key->size);
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res = -ENOKEY;
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up_read(&keyring_key->sem);
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goto out;
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}
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res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
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up_read(&keyring_key->sem);
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if (res)
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goto out;
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crypt_info->ci_keyring_key = keyring_key;
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return 0;
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out:
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key_put(keyring_key);
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return res;
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}
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static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
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const char **cipher_str_ret, int *keysize_ret)
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{
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if (S_ISREG(inode->i_mode)) {
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if (ci->ci_data_mode == FS_ENCRYPTION_MODE_AES_256_XTS) {
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*cipher_str_ret = "xts(aes)";
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*keysize_ret = FS_AES_256_XTS_KEY_SIZE;
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return 0;
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}
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pr_warn_once("fscrypto: unsupported contents encryption mode "
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"%d for inode %lu\n",
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ci->ci_data_mode, inode->i_ino);
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return -ENOKEY;
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}
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if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
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if (ci->ci_filename_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
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*cipher_str_ret = "cts(cbc(aes))";
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*keysize_ret = FS_AES_256_CTS_KEY_SIZE;
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return 0;
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}
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pr_warn_once("fscrypto: unsupported filenames encryption mode "
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"%d for inode %lu\n",
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ci->ci_filename_mode, inode->i_ino);
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return -ENOKEY;
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}
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pr_warn_once("fscrypto: unsupported file type %d for inode %lu\n",
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(inode->i_mode & S_IFMT), inode->i_ino);
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return -ENOKEY;
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}
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static void put_crypt_info(struct fscrypt_info *ci)
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{
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if (!ci)
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return;
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key_put(ci->ci_keyring_key);
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crypto_free_skcipher(ci->ci_ctfm);
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kmem_cache_free(fscrypt_info_cachep, ci);
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}
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int get_crypt_info(struct inode *inode)
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{
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struct fscrypt_info *crypt_info;
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struct fscrypt_context ctx;
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struct crypto_skcipher *ctfm;
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const char *cipher_str;
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int keysize;
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u8 *raw_key = NULL;
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int res;
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res = fscrypt_initialize();
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if (res)
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return res;
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if (!inode->i_sb->s_cop->get_context)
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return -EOPNOTSUPP;
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retry:
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crypt_info = ACCESS_ONCE(inode->i_crypt_info);
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if (crypt_info) {
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if (!crypt_info->ci_keyring_key ||
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key_validate(crypt_info->ci_keyring_key) == 0)
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return 0;
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fscrypt_put_encryption_info(inode, crypt_info);
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goto retry;
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}
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res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
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if (res < 0) {
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if (!fscrypt_dummy_context_enabled(inode))
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return res;
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ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
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ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
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ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
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ctx.flags = 0;
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} else if (res != sizeof(ctx)) {
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return -EINVAL;
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}
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if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
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return -EINVAL;
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if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
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return -EINVAL;
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crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
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if (!crypt_info)
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return -ENOMEM;
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crypt_info->ci_flags = ctx.flags;
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crypt_info->ci_data_mode = ctx.contents_encryption_mode;
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crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
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crypt_info->ci_ctfm = NULL;
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crypt_info->ci_keyring_key = NULL;
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memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
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sizeof(crypt_info->ci_master_key));
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res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
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if (res)
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goto out;
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/*
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* This cannot be a stack buffer because it is passed to the scatterlist
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* crypto API as part of key derivation.
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*/
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res = -ENOMEM;
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raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
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if (!raw_key)
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goto out;
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if (fscrypt_dummy_context_enabled(inode)) {
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memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);
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goto got_key;
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}
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res = validate_user_key(crypt_info, &ctx, raw_key,
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FS_KEY_DESC_PREFIX, FS_KEY_DESC_PREFIX_SIZE);
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if (res && inode->i_sb->s_cop->key_prefix) {
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u8 *prefix = NULL;
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int prefix_size, res2;
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prefix_size = inode->i_sb->s_cop->key_prefix(inode, &prefix);
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res2 = validate_user_key(crypt_info, &ctx, raw_key,
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prefix, prefix_size);
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if (res2) {
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if (res2 == -ENOKEY)
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res = -ENOKEY;
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goto out;
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}
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} else if (res) {
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goto out;
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}
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got_key:
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ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
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if (!ctfm || IS_ERR(ctfm)) {
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res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
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printk(KERN_DEBUG
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"%s: error %d (inode %u) allocating crypto tfm\n",
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__func__, res, (unsigned) inode->i_ino);
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goto out;
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}
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crypt_info->ci_ctfm = ctfm;
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crypto_skcipher_clear_flags(ctfm, ~0);
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crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
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res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
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if (res)
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goto out;
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kzfree(raw_key);
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raw_key = NULL;
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if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {
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put_crypt_info(crypt_info);
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goto retry;
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}
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return 0;
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out:
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if (res == -ENOKEY)
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res = 0;
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put_crypt_info(crypt_info);
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kzfree(raw_key);
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return res;
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}
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void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
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{
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struct fscrypt_info *prev;
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if (ci == NULL)
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ci = ACCESS_ONCE(inode->i_crypt_info);
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if (ci == NULL)
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return;
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prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
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if (prev != ci)
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return;
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put_crypt_info(ci);
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}
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EXPORT_SYMBOL(fscrypt_put_encryption_info);
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int fscrypt_get_encryption_info(struct inode *inode)
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{
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struct fscrypt_info *ci = inode->i_crypt_info;
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if (!ci ||
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(ci->ci_keyring_key &&
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(ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
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(1 << KEY_FLAG_REVOKED) |
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(1 << KEY_FLAG_DEAD)))))
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return get_crypt_info(inode);
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return 0;
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}
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EXPORT_SYMBOL(fscrypt_get_encryption_info);
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