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![Eric Biggers](/assets/img/avatar_default.png)
After FS_IOC_REMOVE_ENCRYPTION_KEY removes a key, it syncs the
filesystem and tries to get and put all inodes that were unlocked by the
key so that unused inodes get evicted via fscrypt_drop_inode().
Normally, the inodes are all clean due to the sync.
However, after the filesystem is sync'ed, userspace can modify and close
one of the files. (Userspace is *supposed* to close the files before
removing the key. But it doesn't always happen, and the kernel can't
assume it.) This causes the inode to be dirtied and have i_count == 0.
Then, fscrypt_drop_inode() failed to consider this case and indicated
that the inode can be dropped, causing the write to be lost.
On f2fs, other problems such as a filesystem freeze could occur due to
the inode being freed while still on f2fs's dirty inode list.
Fix this bug by making fscrypt_drop_inode() only drop clean inodes.
I've written an xfstest which detects this bug on ext4, f2fs, and ubifs.
Fixes: b1c0ec3599
("fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl")
Cc: <stable@vger.kernel.org> # v5.4+
Link: https://lore.kernel.org/r/20200305084138.653498-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
560 lines
16 KiB
C
560 lines
16 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Key setup 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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* Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
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* Heavily modified since then.
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*/
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#include <crypto/skcipher.h>
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#include <linux/key.h>
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#include "fscrypt_private.h"
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struct fscrypt_mode fscrypt_modes[] = {
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[FSCRYPT_MODE_AES_256_XTS] = {
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.friendly_name = "AES-256-XTS",
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.cipher_str = "xts(aes)",
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.keysize = 64,
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.ivsize = 16,
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},
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[FSCRYPT_MODE_AES_256_CTS] = {
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.friendly_name = "AES-256-CTS-CBC",
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.cipher_str = "cts(cbc(aes))",
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.keysize = 32,
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.ivsize = 16,
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},
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[FSCRYPT_MODE_AES_128_CBC] = {
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.friendly_name = "AES-128-CBC-ESSIV",
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.cipher_str = "essiv(cbc(aes),sha256)",
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.keysize = 16,
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.ivsize = 16,
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},
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[FSCRYPT_MODE_AES_128_CTS] = {
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.friendly_name = "AES-128-CTS-CBC",
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.cipher_str = "cts(cbc(aes))",
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.keysize = 16,
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.ivsize = 16,
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},
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[FSCRYPT_MODE_ADIANTUM] = {
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.friendly_name = "Adiantum",
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.cipher_str = "adiantum(xchacha12,aes)",
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.keysize = 32,
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.ivsize = 32,
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},
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};
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static struct fscrypt_mode *
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select_encryption_mode(const union fscrypt_policy *policy,
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const struct inode *inode)
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{
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if (S_ISREG(inode->i_mode))
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return &fscrypt_modes[fscrypt_policy_contents_mode(policy)];
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if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
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return &fscrypt_modes[fscrypt_policy_fnames_mode(policy)];
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WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
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inode->i_ino, (inode->i_mode & S_IFMT));
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return ERR_PTR(-EINVAL);
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}
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/* Create a symmetric cipher object for the given encryption mode and key */
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struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode,
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const u8 *raw_key,
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const struct inode *inode)
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{
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struct crypto_skcipher *tfm;
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int err;
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tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
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if (IS_ERR(tfm)) {
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if (PTR_ERR(tfm) == -ENOENT) {
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fscrypt_warn(inode,
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"Missing crypto API support for %s (API name: \"%s\")",
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mode->friendly_name, mode->cipher_str);
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return ERR_PTR(-ENOPKG);
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}
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fscrypt_err(inode, "Error allocating '%s' transform: %ld",
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mode->cipher_str, PTR_ERR(tfm));
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return tfm;
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}
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if (!xchg(&mode->logged_impl_name, 1)) {
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/*
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* fscrypt performance can vary greatly depending on which
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* crypto algorithm implementation is used. Help people debug
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* performance problems by logging the ->cra_driver_name the
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* first time a mode is used.
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*/
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pr_info("fscrypt: %s using implementation \"%s\"\n",
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mode->friendly_name, crypto_skcipher_driver_name(tfm));
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}
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if (WARN_ON(crypto_skcipher_ivsize(tfm) != mode->ivsize)) {
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err = -EINVAL;
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goto err_free_tfm;
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}
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crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
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err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
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if (err)
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goto err_free_tfm;
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return tfm;
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err_free_tfm:
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crypto_free_skcipher(tfm);
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return ERR_PTR(err);
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}
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/* Given a per-file encryption key, set up the file's crypto transform object */
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int fscrypt_set_per_file_enc_key(struct fscrypt_info *ci, const u8 *raw_key)
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{
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struct crypto_skcipher *tfm;
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tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode);
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if (IS_ERR(tfm))
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return PTR_ERR(tfm);
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ci->ci_ctfm = tfm;
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ci->ci_owns_key = true;
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return 0;
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}
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static int setup_per_mode_enc_key(struct fscrypt_info *ci,
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struct fscrypt_master_key *mk,
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struct crypto_skcipher **tfms,
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u8 hkdf_context, bool include_fs_uuid)
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{
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const struct inode *inode = ci->ci_inode;
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const struct super_block *sb = inode->i_sb;
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struct fscrypt_mode *mode = ci->ci_mode;
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const u8 mode_num = mode - fscrypt_modes;
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struct crypto_skcipher *tfm, *prev_tfm;
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u8 mode_key[FSCRYPT_MAX_KEY_SIZE];
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u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
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unsigned int hkdf_infolen = 0;
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int err;
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if (WARN_ON(mode_num > __FSCRYPT_MODE_MAX))
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return -EINVAL;
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/* pairs with cmpxchg() below */
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tfm = READ_ONCE(tfms[mode_num]);
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if (likely(tfm != NULL))
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goto done;
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BUILD_BUG_ON(sizeof(mode_num) != 1);
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BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
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BUILD_BUG_ON(sizeof(hkdf_info) != 17);
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hkdf_info[hkdf_infolen++] = mode_num;
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if (include_fs_uuid) {
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memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
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sizeof(sb->s_uuid));
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hkdf_infolen += sizeof(sb->s_uuid);
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}
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err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
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hkdf_context, hkdf_info, hkdf_infolen,
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mode_key, mode->keysize);
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if (err)
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return err;
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tfm = fscrypt_allocate_skcipher(mode, mode_key, inode);
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memzero_explicit(mode_key, mode->keysize);
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if (IS_ERR(tfm))
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return PTR_ERR(tfm);
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/* pairs with READ_ONCE() above */
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prev_tfm = cmpxchg(&tfms[mode_num], NULL, tfm);
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if (prev_tfm != NULL) {
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crypto_free_skcipher(tfm);
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tfm = prev_tfm;
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}
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done:
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ci->ci_ctfm = tfm;
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return 0;
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}
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int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
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const struct fscrypt_master_key *mk)
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{
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int err;
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err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, HKDF_CONTEXT_DIRHASH_KEY,
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ci->ci_nonce, FS_KEY_DERIVATION_NONCE_SIZE,
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(u8 *)&ci->ci_dirhash_key,
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sizeof(ci->ci_dirhash_key));
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if (err)
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return err;
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ci->ci_dirhash_key_initialized = true;
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return 0;
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}
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static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
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struct fscrypt_master_key *mk)
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{
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int err;
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if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
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/*
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* DIRECT_KEY: instead of deriving per-file encryption keys, the
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* per-file nonce will be included in all the IVs. But unlike
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* v1 policies, for v2 policies in this case we don't encrypt
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* with the master key directly but rather derive a per-mode
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* encryption key. This ensures that the master key is
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* consistently used only for HKDF, avoiding key reuse issues.
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*/
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err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_tfms,
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HKDF_CONTEXT_DIRECT_KEY, false);
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} else if (ci->ci_policy.v2.flags &
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FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
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/*
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* IV_INO_LBLK_64: encryption keys are derived from (master_key,
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* mode_num, filesystem_uuid), and inode number is included in
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* the IVs. This format is optimized for use with inline
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* encryption hardware compliant with the UFS or eMMC standards.
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*/
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err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_tfms,
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HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
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true);
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} else {
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u8 derived_key[FSCRYPT_MAX_KEY_SIZE];
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err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
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HKDF_CONTEXT_PER_FILE_ENC_KEY,
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ci->ci_nonce,
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FS_KEY_DERIVATION_NONCE_SIZE,
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derived_key, ci->ci_mode->keysize);
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if (err)
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return err;
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err = fscrypt_set_per_file_enc_key(ci, derived_key);
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memzero_explicit(derived_key, ci->ci_mode->keysize);
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}
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if (err)
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return err;
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/* Derive a secret dirhash key for directories that need it. */
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if (S_ISDIR(ci->ci_inode->i_mode) && IS_CASEFOLDED(ci->ci_inode)) {
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err = fscrypt_derive_dirhash_key(ci, mk);
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if (err)
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return err;
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}
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return 0;
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}
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/*
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* Find the master key, then set up the inode's actual encryption key.
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*
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* If the master key is found in the filesystem-level keyring, then the
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* corresponding 'struct key' is returned in *master_key_ret with
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* ->mk_secret_sem read-locked. This is needed to ensure that only one task
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* links the fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race
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* to create an fscrypt_info for the same inode), and to synchronize the master
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* key being removed with a new inode starting to use it.
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*/
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static int setup_file_encryption_key(struct fscrypt_info *ci,
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struct key **master_key_ret)
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{
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struct key *key;
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struct fscrypt_master_key *mk = NULL;
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struct fscrypt_key_specifier mk_spec;
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int err;
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switch (ci->ci_policy.version) {
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case FSCRYPT_POLICY_V1:
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mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
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memcpy(mk_spec.u.descriptor,
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ci->ci_policy.v1.master_key_descriptor,
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FSCRYPT_KEY_DESCRIPTOR_SIZE);
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break;
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case FSCRYPT_POLICY_V2:
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mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
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memcpy(mk_spec.u.identifier,
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ci->ci_policy.v2.master_key_identifier,
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FSCRYPT_KEY_IDENTIFIER_SIZE);
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break;
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default:
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WARN_ON(1);
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return -EINVAL;
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}
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key = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
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if (IS_ERR(key)) {
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if (key != ERR_PTR(-ENOKEY) ||
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ci->ci_policy.version != FSCRYPT_POLICY_V1)
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return PTR_ERR(key);
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/*
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* As a legacy fallback for v1 policies, search for the key in
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* the current task's subscribed keyrings too. Don't move this
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* to before the search of ->s_master_keys, since users
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* shouldn't be able to override filesystem-level keys.
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*/
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return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
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}
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mk = key->payload.data[0];
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down_read(&mk->mk_secret_sem);
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/* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */
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if (!is_master_key_secret_present(&mk->mk_secret)) {
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err = -ENOKEY;
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goto out_release_key;
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}
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/*
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* Require that the master key be at least as long as the derived key.
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* Otherwise, the derived key cannot possibly contain as much entropy as
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* that required by the encryption mode it will be used for. For v1
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* policies it's also required for the KDF to work at all.
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*/
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if (mk->mk_secret.size < ci->ci_mode->keysize) {
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fscrypt_warn(NULL,
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"key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
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master_key_spec_type(&mk_spec),
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master_key_spec_len(&mk_spec), (u8 *)&mk_spec.u,
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mk->mk_secret.size, ci->ci_mode->keysize);
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err = -ENOKEY;
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goto out_release_key;
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}
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switch (ci->ci_policy.version) {
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case FSCRYPT_POLICY_V1:
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err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
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break;
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case FSCRYPT_POLICY_V2:
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err = fscrypt_setup_v2_file_key(ci, mk);
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break;
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default:
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WARN_ON(1);
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err = -EINVAL;
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break;
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}
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if (err)
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goto out_release_key;
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*master_key_ret = key;
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return 0;
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out_release_key:
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up_read(&mk->mk_secret_sem);
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key_put(key);
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return err;
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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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struct key *key;
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if (!ci)
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return;
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if (ci->ci_direct_key)
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fscrypt_put_direct_key(ci->ci_direct_key);
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else if (ci->ci_owns_key)
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crypto_free_skcipher(ci->ci_ctfm);
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key = ci->ci_master_key;
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if (key) {
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struct fscrypt_master_key *mk = key->payload.data[0];
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/*
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* Remove this inode from the list of inodes that were unlocked
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* with the master key.
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*
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* In addition, if we're removing the last inode from a key that
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* already had its secret removed, invalidate the key so that it
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* gets removed from ->s_master_keys.
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*/
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spin_lock(&mk->mk_decrypted_inodes_lock);
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list_del(&ci->ci_master_key_link);
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spin_unlock(&mk->mk_decrypted_inodes_lock);
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if (refcount_dec_and_test(&mk->mk_refcount))
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key_invalidate(key);
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key_put(key);
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}
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memzero_explicit(ci, sizeof(*ci));
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kmem_cache_free(fscrypt_info_cachep, ci);
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}
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int fscrypt_get_encryption_info(struct inode *inode)
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{
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struct fscrypt_info *crypt_info;
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union fscrypt_context ctx;
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struct fscrypt_mode *mode;
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struct key *master_key = NULL;
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int res;
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if (fscrypt_has_encryption_key(inode))
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return 0;
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res = fscrypt_initialize(inode->i_sb->s_cop->flags);
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if (res)
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return res;
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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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IS_ENCRYPTED(inode)) {
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fscrypt_warn(inode,
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"Error %d getting encryption context",
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res);
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return res;
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}
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/* Fake up a context for an unencrypted directory */
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memset(&ctx, 0, sizeof(ctx));
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ctx.version = FSCRYPT_CONTEXT_V1;
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ctx.v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
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ctx.v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
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memset(ctx.v1.master_key_descriptor, 0x42,
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FSCRYPT_KEY_DESCRIPTOR_SIZE);
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res = sizeof(ctx.v1);
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}
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crypt_info = kmem_cache_zalloc(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_inode = inode;
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res = fscrypt_policy_from_context(&crypt_info->ci_policy, &ctx, res);
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if (res) {
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fscrypt_warn(inode,
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"Unrecognized or corrupt encryption context");
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goto out;
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}
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switch (ctx.version) {
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case FSCRYPT_CONTEXT_V1:
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memcpy(crypt_info->ci_nonce, ctx.v1.nonce,
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FS_KEY_DERIVATION_NONCE_SIZE);
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break;
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case FSCRYPT_CONTEXT_V2:
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memcpy(crypt_info->ci_nonce, ctx.v2.nonce,
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FS_KEY_DERIVATION_NONCE_SIZE);
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break;
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default:
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WARN_ON(1);
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res = -EINVAL;
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goto out;
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}
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if (!fscrypt_supported_policy(&crypt_info->ci_policy, inode)) {
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res = -EINVAL;
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goto out;
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}
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mode = select_encryption_mode(&crypt_info->ci_policy, inode);
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if (IS_ERR(mode)) {
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res = PTR_ERR(mode);
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goto out;
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}
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WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
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crypt_info->ci_mode = mode;
|
|
|
|
res = setup_file_encryption_key(crypt_info, &master_key);
|
|
if (res)
|
|
goto out;
|
|
|
|
if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
|
|
if (master_key) {
|
|
struct fscrypt_master_key *mk =
|
|
master_key->payload.data[0];
|
|
|
|
refcount_inc(&mk->mk_refcount);
|
|
crypt_info->ci_master_key = key_get(master_key);
|
|
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 (master_key) {
|
|
struct fscrypt_master_key *mk = master_key->payload.data[0];
|
|
|
|
up_read(&mk->mk_secret_sem);
|
|
key_put(master_key);
|
|
}
|
|
if (res == -ENOKEY)
|
|
res = 0;
|
|
put_crypt_info(crypt_info);
|
|
return res;
|
|
}
|
|
EXPORT_SYMBOL(fscrypt_get_encryption_info);
|
|
|
|
/**
|
|
* fscrypt_put_encryption_info - free most of an inode's fscrypt data
|
|
*
|
|
* Free the inode's fscrypt_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
|
|
*
|
|
* 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
|
|
*
|
|
* 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_info *ci = READ_ONCE(inode->i_crypt_info);
|
|
const struct fscrypt_master_key *mk;
|
|
|
|
/*
|
|
* 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;
|
|
mk = ci->ci_master_key->payload.data[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;
|
|
|
|
/*
|
|
* Note: since we aren't holding ->mk_secret_sem, the result here can
|
|
* 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 !is_master_key_secret_present(&mk->mk_secret);
|
|
}
|
|
EXPORT_SYMBOL_GPL(fscrypt_drop_inode);
|