linux/fs/crypto/keysetup.c
Eric Biggers 15baf55481 fscrypt: track master key presence separately from secret
Master keys can be in one of three states: present, incompletely
removed, and absent (as per FSCRYPT_KEY_STATUS_* used in the UAPI).
Currently, the way that "present" is distinguished from "incompletely
removed" internally is by whether ->mk_secret exists or not.

With extent-based encryption, it will be necessary to allow per-extent
keys to be derived while the master key is incompletely removed, so that
I/O on open files will reliably continue working after removal of the
key has been initiated.  (We could allow I/O to sometimes fail in that
case, but that seems problematic for reasons such as writes getting
silently thrown away and diverging from the existing fscrypt semantics.)
Therefore, when the filesystem is using extent-based encryption,
->mk_secret can't be wiped when the key becomes incompletely removed.

As a prerequisite for doing that, this patch makes the "present" state
be tracked using a new field, ->mk_present.  No behavior is changed yet.

The basic idea here is borrowed from Josef Bacik's patch
"fscrypt: use a flag to indicate that the master key is being evicted"
(https://lore.kernel.org/r/e86c16dddc049ff065f877d793ad773e4c6bfad9.1696970227.git.josef@toxicpanda.com).
I reimplemented it using a "present" bool instead of an "evicted" flag,
fixed a couple bugs, and tried to update everything to be consistent.

Note: I considered adding a ->mk_status field instead, holding one of
FSCRYPT_KEY_STATUS_*.  At first that seemed nice, but it ended up being
more complex (despite simplifying FS_IOC_GET_ENCRYPTION_KEY_STATUS),
since it would have introduced redundancy and had weird locking rules.

Reviewed-by: Neal Gompa <neal@gompa.dev>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20231015061055.62673-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
2023-10-16 21:23:45 -07:00

815 lines
24 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Key setup facility for FS encryption support.
*
* Copyright (C) 2015, Google, Inc.
*
* Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
* Heavily modified since then.
*/
#include <crypto/skcipher.h>
#include <linux/random.h>
#include "fscrypt_private.h"
struct fscrypt_mode fscrypt_modes[] = {
[FSCRYPT_MODE_AES_256_XTS] = {
.friendly_name = "AES-256-XTS",
.cipher_str = "xts(aes)",
.keysize = 64,
.security_strength = 32,
.ivsize = 16,
.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS,
},
[FSCRYPT_MODE_AES_256_CTS] = {
.friendly_name = "AES-256-CTS-CBC",
.cipher_str = "cts(cbc(aes))",
.keysize = 32,
.security_strength = 32,
.ivsize = 16,
},
[FSCRYPT_MODE_AES_128_CBC] = {
.friendly_name = "AES-128-CBC-ESSIV",
.cipher_str = "essiv(cbc(aes),sha256)",
.keysize = 16,
.security_strength = 16,
.ivsize = 16,
.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV,
},
[FSCRYPT_MODE_AES_128_CTS] = {
.friendly_name = "AES-128-CTS-CBC",
.cipher_str = "cts(cbc(aes))",
.keysize = 16,
.security_strength = 16,
.ivsize = 16,
},
[FSCRYPT_MODE_SM4_XTS] = {
.friendly_name = "SM4-XTS",
.cipher_str = "xts(sm4)",
.keysize = 32,
.security_strength = 16,
.ivsize = 16,
.blk_crypto_mode = BLK_ENCRYPTION_MODE_SM4_XTS,
},
[FSCRYPT_MODE_SM4_CTS] = {
.friendly_name = "SM4-CTS-CBC",
.cipher_str = "cts(cbc(sm4))",
.keysize = 16,
.security_strength = 16,
.ivsize = 16,
},
[FSCRYPT_MODE_ADIANTUM] = {
.friendly_name = "Adiantum",
.cipher_str = "adiantum(xchacha12,aes)",
.keysize = 32,
.security_strength = 32,
.ivsize = 32,
.blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM,
},
[FSCRYPT_MODE_AES_256_HCTR2] = {
.friendly_name = "AES-256-HCTR2",
.cipher_str = "hctr2(aes)",
.keysize = 32,
.security_strength = 32,
.ivsize = 32,
},
};
static DEFINE_MUTEX(fscrypt_mode_key_setup_mutex);
static struct fscrypt_mode *
select_encryption_mode(const union fscrypt_policy *policy,
const struct inode *inode)
{
BUILD_BUG_ON(ARRAY_SIZE(fscrypt_modes) != FSCRYPT_MODE_MAX + 1);
if (S_ISREG(inode->i_mode))
return &fscrypt_modes[fscrypt_policy_contents_mode(policy)];
if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
return &fscrypt_modes[fscrypt_policy_fnames_mode(policy)];
WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
inode->i_ino, (inode->i_mode & S_IFMT));
return ERR_PTR(-EINVAL);
}
/* Create a symmetric cipher object for the given encryption mode and key */
static struct crypto_skcipher *
fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
const struct inode *inode)
{
struct crypto_skcipher *tfm;
int err;
tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
if (IS_ERR(tfm)) {
if (PTR_ERR(tfm) == -ENOENT) {
fscrypt_warn(inode,
"Missing crypto API support for %s (API name: \"%s\")",
mode->friendly_name, mode->cipher_str);
return ERR_PTR(-ENOPKG);
}
fscrypt_err(inode, "Error allocating '%s' transform: %ld",
mode->cipher_str, PTR_ERR(tfm));
return tfm;
}
if (!xchg(&mode->logged_cryptoapi_impl, 1)) {
/*
* fscrypt performance can vary greatly depending on which
* crypto algorithm implementation is used. Help people debug
* performance problems by logging the ->cra_driver_name the
* first time a mode is used.
*/
pr_info("fscrypt: %s using implementation \"%s\"\n",
mode->friendly_name, crypto_skcipher_driver_name(tfm));
}
if (WARN_ON_ONCE(crypto_skcipher_ivsize(tfm) != mode->ivsize)) {
err = -EINVAL;
goto err_free_tfm;
}
crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
if (err)
goto err_free_tfm;
return tfm;
err_free_tfm:
crypto_free_skcipher(tfm);
return ERR_PTR(err);
}
/*
* Prepare the crypto transform object or blk-crypto key in @prep_key, given the
* raw key, encryption mode (@ci->ci_mode), flag indicating which encryption
* implementation (fs-layer or blk-crypto) will be used (@ci->ci_inlinecrypt),
* and IV generation method (@ci->ci_policy.flags).
*/
int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,
const u8 *raw_key, const struct fscrypt_inode_info *ci)
{
struct crypto_skcipher *tfm;
if (fscrypt_using_inline_encryption(ci))
return fscrypt_prepare_inline_crypt_key(prep_key, raw_key, ci);
tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode);
if (IS_ERR(tfm))
return PTR_ERR(tfm);
/*
* Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
* I.e., here we publish ->tfm with a RELEASE barrier so that
* concurrent tasks can ACQUIRE it. Note that this concurrency is only
* possible for per-mode keys, not for per-file keys.
*/
smp_store_release(&prep_key->tfm, tfm);
return 0;
}
/* Destroy a crypto transform object and/or blk-crypto key. */
void fscrypt_destroy_prepared_key(struct super_block *sb,
struct fscrypt_prepared_key *prep_key)
{
crypto_free_skcipher(prep_key->tfm);
fscrypt_destroy_inline_crypt_key(sb, prep_key);
memzero_explicit(prep_key, sizeof(*prep_key));
}
/* Given a per-file encryption key, set up the file's crypto transform object */
int fscrypt_set_per_file_enc_key(struct fscrypt_inode_info *ci,
const u8 *raw_key)
{
ci->ci_owns_key = true;
return fscrypt_prepare_key(&ci->ci_enc_key, raw_key, ci);
}
static int setup_per_mode_enc_key(struct fscrypt_inode_info *ci,
struct fscrypt_master_key *mk,
struct fscrypt_prepared_key *keys,
u8 hkdf_context, bool include_fs_uuid)
{
const struct inode *inode = ci->ci_inode;
const struct super_block *sb = inode->i_sb;
struct fscrypt_mode *mode = ci->ci_mode;
const u8 mode_num = mode - fscrypt_modes;
struct fscrypt_prepared_key *prep_key;
u8 mode_key[FSCRYPT_MAX_KEY_SIZE];
u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
unsigned int hkdf_infolen = 0;
int err;
if (WARN_ON_ONCE(mode_num > FSCRYPT_MODE_MAX))
return -EINVAL;
prep_key = &keys[mode_num];
if (fscrypt_is_key_prepared(prep_key, ci)) {
ci->ci_enc_key = *prep_key;
return 0;
}
mutex_lock(&fscrypt_mode_key_setup_mutex);
if (fscrypt_is_key_prepared(prep_key, ci))
goto done_unlock;
BUILD_BUG_ON(sizeof(mode_num) != 1);
BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
BUILD_BUG_ON(sizeof(hkdf_info) != 17);
hkdf_info[hkdf_infolen++] = mode_num;
if (include_fs_uuid) {
memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
sizeof(sb->s_uuid));
hkdf_infolen += sizeof(sb->s_uuid);
}
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
hkdf_context, hkdf_info, hkdf_infolen,
mode_key, mode->keysize);
if (err)
goto out_unlock;
err = fscrypt_prepare_key(prep_key, mode_key, ci);
memzero_explicit(mode_key, mode->keysize);
if (err)
goto out_unlock;
done_unlock:
ci->ci_enc_key = *prep_key;
err = 0;
out_unlock:
mutex_unlock(&fscrypt_mode_key_setup_mutex);
return err;
}
/*
* Derive a SipHash key from the given fscrypt master key and the given
* application-specific information string.
*
* Note that the KDF produces a byte array, but the SipHash APIs expect the key
* as a pair of 64-bit words. Therefore, on big endian CPUs we have to do an
* endianness swap in order to get the same results as on little endian CPUs.
*/
static int fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk,
u8 context, const u8 *info,
unsigned int infolen, siphash_key_t *key)
{
int err;
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,
(u8 *)key, sizeof(*key));
if (err)
return err;
BUILD_BUG_ON(sizeof(*key) != 16);
BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);
le64_to_cpus(&key->key[0]);
le64_to_cpus(&key->key[1]);
return 0;
}
int fscrypt_derive_dirhash_key(struct fscrypt_inode_info *ci,
const struct fscrypt_master_key *mk)
{
int err;
err = fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
&ci->ci_dirhash_key);
if (err)
return err;
ci->ci_dirhash_key_initialized = true;
return 0;
}
void fscrypt_hash_inode_number(struct fscrypt_inode_info *ci,
const struct fscrypt_master_key *mk)
{
WARN_ON_ONCE(ci->ci_inode->i_ino == 0);
WARN_ON_ONCE(!mk->mk_ino_hash_key_initialized);
ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino,
&mk->mk_ino_hash_key);
}
static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info *ci,
struct fscrypt_master_key *mk)
{
int err;
err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
if (err)
return err;
/* pairs with smp_store_release() below */
if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) {
mutex_lock(&fscrypt_mode_key_setup_mutex);
if (mk->mk_ino_hash_key_initialized)
goto unlock;
err = fscrypt_derive_siphash_key(mk,
HKDF_CONTEXT_INODE_HASH_KEY,
NULL, 0, &mk->mk_ino_hash_key);
if (err)
goto unlock;
/* pairs with smp_load_acquire() above */
smp_store_release(&mk->mk_ino_hash_key_initialized, true);
unlock:
mutex_unlock(&fscrypt_mode_key_setup_mutex);
if (err)
return err;
}
/*
* New inodes may not have an inode number assigned yet.
* Hashing their inode number is delayed until later.
*/
if (ci->ci_inode->i_ino)
fscrypt_hash_inode_number(ci, mk);
return 0;
}
static int fscrypt_setup_v2_file_key(struct fscrypt_inode_info *ci,
struct fscrypt_master_key *mk,
bool need_dirhash_key)
{
int err;
if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
/*
* DIRECT_KEY: instead of deriving per-file encryption keys, the
* per-file nonce will be included in all the IVs. But unlike
* v1 policies, for v2 policies in this case we don't encrypt
* with the master key directly but rather derive a per-mode
* encryption key. This ensures that the master key is
* consistently used only for HKDF, avoiding key reuse issues.
*/
err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,
HKDF_CONTEXT_DIRECT_KEY, false);
} else if (ci->ci_policy.v2.flags &
FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
/*
* IV_INO_LBLK_64: encryption keys are derived from (master_key,
* mode_num, filesystem_uuid), and inode number is included in
* the IVs. This format is optimized for use with inline
* encryption hardware compliant with the UFS standard.
*/
err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,
HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
true);
} else if (ci->ci_policy.v2.flags &
FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);
} else {
u8 derived_key[FSCRYPT_MAX_KEY_SIZE];
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
HKDF_CONTEXT_PER_FILE_ENC_KEY,
ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
derived_key, ci->ci_mode->keysize);
if (err)
return err;
err = fscrypt_set_per_file_enc_key(ci, derived_key);
memzero_explicit(derived_key, ci->ci_mode->keysize);
}
if (err)
return err;
/* Derive a secret dirhash key for directories that need it. */
if (need_dirhash_key) {
err = fscrypt_derive_dirhash_key(ci, mk);
if (err)
return err;
}
return 0;
}
/*
* Check whether the size of the given master key (@mk) is appropriate for the
* encryption settings which a particular file will use (@ci).
*
* If the file uses a v1 encryption policy, then the master key must be at least
* as long as the derived key, as this is a requirement of the v1 KDF.
*
* Otherwise, the KDF can accept any size key, so we enforce a slightly looser
* requirement: we require that the size of the master key be at least the
* maximum security strength of any algorithm whose key will be derived from it
* (but in practice we only need to consider @ci->ci_mode, since any other
* possible subkeys such as DIRHASH and INODE_HASH will never increase the
* required key size over @ci->ci_mode). This allows AES-256-XTS keys to be
* derived from a 256-bit master key, which is cryptographically sufficient,
* rather than requiring a 512-bit master key which is unnecessarily long. (We
* still allow 512-bit master keys if the user chooses to use them, though.)
*/
static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk,
const struct fscrypt_inode_info *ci)
{
unsigned int min_keysize;
if (ci->ci_policy.version == FSCRYPT_POLICY_V1)
min_keysize = ci->ci_mode->keysize;
else
min_keysize = ci->ci_mode->security_strength;
if (mk->mk_secret.size < min_keysize) {
fscrypt_warn(NULL,
"key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
master_key_spec_type(&mk->mk_spec),
master_key_spec_len(&mk->mk_spec),
(u8 *)&mk->mk_spec.u,
mk->mk_secret.size, min_keysize);
return false;
}
return true;
}
/*
* Find the master key, then set up the inode's actual encryption key.
*
* If the master key is found in the filesystem-level keyring, then it is
* returned in *mk_ret with its semaphore read-locked. This is needed to ensure
* that only one task links the fscrypt_inode_info into ->mk_decrypted_inodes
* (as multiple tasks may race to create an fscrypt_inode_info for the same
* inode), and to synchronize the master key being removed with a new inode
* starting to use it.
*/
static int setup_file_encryption_key(struct fscrypt_inode_info *ci,
bool need_dirhash_key,
struct fscrypt_master_key **mk_ret)
{
struct super_block *sb = ci->ci_inode->i_sb;
struct fscrypt_key_specifier mk_spec;
struct fscrypt_master_key *mk;
int err;
err = fscrypt_select_encryption_impl(ci);
if (err)
return err;
err = fscrypt_policy_to_key_spec(&ci->ci_policy, &mk_spec);
if (err)
return err;
mk = fscrypt_find_master_key(sb, &mk_spec);
if (unlikely(!mk)) {
const union fscrypt_policy *dummy_policy =
fscrypt_get_dummy_policy(sb);
/*
* Add the test_dummy_encryption key on-demand. In principle,
* it should be added at mount time. Do it here instead so that
* the individual filesystems don't need to worry about adding
* this key at mount time and cleaning up on mount failure.
*/
if (dummy_policy &&
fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
err = fscrypt_add_test_dummy_key(sb, &mk_spec);
if (err)
return err;
mk = fscrypt_find_master_key(sb, &mk_spec);
}
}
if (unlikely(!mk)) {
if (ci->ci_policy.version != FSCRYPT_POLICY_V1)
return -ENOKEY;
/*
* As a legacy fallback for v1 policies, search for the key in
* the current task's subscribed keyrings too. Don't move this
* to before the search of ->s_master_keys, since users
* shouldn't be able to override filesystem-level keys.
*/
return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
}
down_read(&mk->mk_sem);
if (!mk->mk_present) {
/* FS_IOC_REMOVE_ENCRYPTION_KEY has been executed on this key */
err = -ENOKEY;
goto out_release_key;
}
if (!fscrypt_valid_master_key_size(mk, ci)) {
err = -ENOKEY;
goto out_release_key;
}
switch (ci->ci_policy.version) {
case FSCRYPT_POLICY_V1:
err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
break;
case FSCRYPT_POLICY_V2:
err = fscrypt_setup_v2_file_key(ci, mk, need_dirhash_key);
break;
default:
WARN_ON_ONCE(1);
err = -EINVAL;
break;
}
if (err)
goto out_release_key;
*mk_ret = mk;
return 0;
out_release_key:
up_read(&mk->mk_sem);
fscrypt_put_master_key(mk);
return err;
}
static void put_crypt_info(struct fscrypt_inode_info *ci)
{
struct fscrypt_master_key *mk;
if (!ci)
return;
if (ci->ci_direct_key)
fscrypt_put_direct_key(ci->ci_direct_key);
else if (ci->ci_owns_key)
fscrypt_destroy_prepared_key(ci->ci_inode->i_sb,
&ci->ci_enc_key);
mk = ci->ci_master_key;
if (mk) {
/*
* Remove this inode from the list of inodes that were unlocked
* with the master key. In addition, if we're removing the last
* inode from an incompletely removed key, then complete the
* full removal of the key.
*/
spin_lock(&mk->mk_decrypted_inodes_lock);
list_del(&ci->ci_master_key_link);
spin_unlock(&mk->mk_decrypted_inodes_lock);
fscrypt_put_master_key_activeref(ci->ci_inode->i_sb, mk);
}
memzero_explicit(ci, sizeof(*ci));
kmem_cache_free(fscrypt_inode_info_cachep, ci);
}
static int
fscrypt_setup_encryption_info(struct inode *inode,
const union fscrypt_policy *policy,
const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],
bool need_dirhash_key)
{
struct fscrypt_inode_info *crypt_info;
struct fscrypt_mode *mode;
struct fscrypt_master_key *mk = NULL;
int res;
res = fscrypt_initialize(inode->i_sb);
if (res)
return res;
crypt_info = kmem_cache_zalloc(fscrypt_inode_info_cachep, GFP_KERNEL);
if (!crypt_info)
return -ENOMEM;
crypt_info->ci_inode = inode;
crypt_info->ci_policy = *policy;
memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
mode = select_encryption_mode(&crypt_info->ci_policy, inode);
if (IS_ERR(mode)) {
res = PTR_ERR(mode);
goto out;
}
WARN_ON_ONCE(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
crypt_info->ci_mode = mode;
crypt_info->ci_data_unit_bits =
fscrypt_policy_du_bits(&crypt_info->ci_policy, inode);
crypt_info->ci_data_units_per_block_bits =
inode->i_blkbits - crypt_info->ci_data_unit_bits;
res = setup_file_encryption_key(crypt_info, need_dirhash_key, &mk);
if (res)
goto out;
/*
* For existing inodes, multiple tasks may race to set ->i_crypt_info.
* So use cmpxchg_release(). This pairs with the smp_load_acquire() in
* fscrypt_get_inode_info(). I.e., here we publish ->i_crypt_info with
* a RELEASE barrier so that other tasks can ACQUIRE it.
*/
if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
/*
* We won the race and set ->i_crypt_info to our crypt_info.
* Now link it into the master key's inode list.
*/
if (mk) {
crypt_info->ci_master_key = mk;
refcount_inc(&mk->mk_active_refs);
spin_lock(&mk->mk_decrypted_inodes_lock);
list_add(&crypt_info->ci_master_key_link,
&mk->mk_decrypted_inodes);
spin_unlock(&mk->mk_decrypted_inodes_lock);
}
crypt_info = NULL;
}
res = 0;
out:
if (mk) {
up_read(&mk->mk_sem);
fscrypt_put_master_key(mk);
}
put_crypt_info(crypt_info);
return res;
}
/**
* fscrypt_get_encryption_info() - set up an inode's encryption key
* @inode: the inode to set up the key for. Must be encrypted.
* @allow_unsupported: if %true, treat an unsupported encryption policy (or
* unrecognized encryption context) the same way as the key
* being unavailable, instead of returning an error. Use
* %false unless the operation being performed is needed in
* order for files (or directories) to be deleted.
*
* Set up ->i_crypt_info, if it hasn't already been done.
*
* Note: unless ->i_crypt_info is already set, this isn't %GFP_NOFS-safe. So
* generally this shouldn't be called from within a filesystem transaction.
*
* Return: 0 if ->i_crypt_info was set or was already set, *or* if the
* encryption key is unavailable. (Use fscrypt_has_encryption_key() to
* distinguish these cases.) Also can return another -errno code.
*/
int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
{
int res;
union fscrypt_context ctx;
union fscrypt_policy policy;
if (fscrypt_has_encryption_key(inode))
return 0;
res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
if (res < 0) {
if (res == -ERANGE && allow_unsupported)
return 0;
fscrypt_warn(inode, "Error %d getting encryption context", res);
return res;
}
res = fscrypt_policy_from_context(&policy, &ctx, res);
if (res) {
if (allow_unsupported)
return 0;
fscrypt_warn(inode,
"Unrecognized or corrupt encryption context");
return res;
}
if (!fscrypt_supported_policy(&policy, inode)) {
if (allow_unsupported)
return 0;
return -EINVAL;
}
res = fscrypt_setup_encryption_info(inode, &policy,
fscrypt_context_nonce(&ctx),
IS_CASEFOLDED(inode) &&
S_ISDIR(inode->i_mode));
if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
res = 0;
if (res == -ENOKEY)
res = 0;
return res;
}
/**
* fscrypt_prepare_new_inode() - prepare to create a new inode in a directory
* @dir: a possibly-encrypted directory
* @inode: the new inode. ->i_mode must be set already.
* ->i_ino doesn't need to be set yet.
* @encrypt_ret: (output) set to %true if the new inode will be encrypted
*
* If the directory is encrypted, set up its ->i_crypt_info in preparation for
* encrypting the name of the new file. Also, if the new inode will be
* encrypted, set up its ->i_crypt_info and set *encrypt_ret=true.
*
* This isn't %GFP_NOFS-safe, and therefore it should be called before starting
* any filesystem transaction to create the inode. For this reason, ->i_ino
* isn't required to be set yet, as the filesystem may not have set it yet.
*
* This doesn't persist the new inode's encryption context. That still needs to
* be done later by calling fscrypt_set_context().
*
* Return: 0 on success, -ENOKEY if the encryption key is missing, or another
* -errno code
*/
int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
bool *encrypt_ret)
{
const union fscrypt_policy *policy;
u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
policy = fscrypt_policy_to_inherit(dir);
if (policy == NULL)
return 0;
if (IS_ERR(policy))
return PTR_ERR(policy);
if (WARN_ON_ONCE(inode->i_mode == 0))
return -EINVAL;
/*
* Only regular files, directories, and symlinks are encrypted.
* Special files like device nodes and named pipes aren't.
*/
if (!S_ISREG(inode->i_mode) &&
!S_ISDIR(inode->i_mode) &&
!S_ISLNK(inode->i_mode))
return 0;
*encrypt_ret = true;
get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
return fscrypt_setup_encryption_info(inode, policy, nonce,
IS_CASEFOLDED(dir) &&
S_ISDIR(inode->i_mode));
}
EXPORT_SYMBOL_GPL(fscrypt_prepare_new_inode);
/**
* fscrypt_put_encryption_info() - free most of an inode's fscrypt data
* @inode: an inode being evicted
*
* Free the inode's fscrypt_inode_info. Filesystems must call this when the
* inode is being evicted. An RCU grace period need not have elapsed yet.
*/
void fscrypt_put_encryption_info(struct inode *inode)
{
put_crypt_info(inode->i_crypt_info);
inode->i_crypt_info = NULL;
}
EXPORT_SYMBOL(fscrypt_put_encryption_info);
/**
* fscrypt_free_inode() - free an inode's fscrypt data requiring RCU delay
* @inode: an inode being freed
*
* Free the inode's cached decrypted symlink target, if any. Filesystems must
* call this after an RCU grace period, just before they free the inode.
*/
void fscrypt_free_inode(struct inode *inode)
{
if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
kfree(inode->i_link);
inode->i_link = NULL;
}
}
EXPORT_SYMBOL(fscrypt_free_inode);
/**
* fscrypt_drop_inode() - check whether the inode's master key has been removed
* @inode: an inode being considered for eviction
*
* Filesystems supporting fscrypt must call this from their ->drop_inode()
* method so that encrypted inodes are evicted as soon as they're no longer in
* use and their master key has been removed.
*
* Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
*/
int fscrypt_drop_inode(struct inode *inode)
{
const struct fscrypt_inode_info *ci = fscrypt_get_inode_info(inode);
/*
* If ci is NULL, then the inode doesn't have an encryption key set up
* so it's irrelevant. If ci_master_key is NULL, then the master key
* was provided via the legacy mechanism of the process-subscribed
* keyrings, so we don't know whether it's been removed or not.
*/
if (!ci || !ci->ci_master_key)
return 0;
/*
* With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
* protected by the key were cleaned by sync_filesystem(). But if
* userspace is still using the files, inodes can be dirtied between
* then and now. We mustn't lose any writes, so skip dirty inodes here.
*/
if (inode->i_state & I_DIRTY_ALL)
return 0;
/*
* We can't take ->mk_sem here, since this runs in atomic context.
* Therefore, ->mk_present can change concurrently, and our result may
* immediately become outdated. But there's no correctness problem with
* unnecessarily evicting. Nor is there a correctness problem with not
* evicting while iput() is racing with the key being removed, since
* then the thread removing the key will either evict the inode itself
* or will correctly detect that it wasn't evicted due to the race.
*/
return !READ_ONCE(ci->ci_master_key->mk_present);
}
EXPORT_SYMBOL_GPL(fscrypt_drop_inode);