// SPDX-License-Identifier: GPL-2.0
/*
 * key management facility for FS encryption support.
 *
 * Copyright (C) 2015, Google, Inc.
 *
 * This contains encryption key functions.
 *
 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
 */

#include <keys/user-type.h>
#include <linux/hashtable.h>
#include <linux/scatterlist.h>
#include <linux/ratelimit.h>
#include <crypto/aes.h>
#include <crypto/algapi.h>
#include <crypto/sha.h>
#include <crypto/skcipher.h>
#include "fscrypt_private.h"

static struct crypto_shash *essiv_hash_tfm;

/* Table of keys referenced by FS_POLICY_FLAG_DIRECT_KEY policies */
static DEFINE_HASHTABLE(fscrypt_master_keys, 6); /* 6 bits = 64 buckets */
static DEFINE_SPINLOCK(fscrypt_master_keys_lock);

/*
 * Key derivation function.  This generates the derived key by encrypting the
 * master key with AES-128-ECB using the inode's nonce as the AES key.
 *
 * The master key must be at least as long as the derived key.  If the master
 * key is longer, then only the first 'derived_keysize' bytes are used.
 */
static int derive_key_aes(const u8 *master_key,
                          const struct fscrypt_context *ctx,
                          u8 *derived_key, unsigned int derived_keysize)
{
        int res = 0;
        struct skcipher_request *req = NULL;
        DECLARE_CRYPTO_WAIT(wait);
        struct scatterlist src_sg, dst_sg;
        struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);

        if (IS_ERR(tfm)) {
                res = PTR_ERR(tfm);
                tfm = NULL;
                goto out;
        }
        crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
        req = skcipher_request_alloc(tfm, GFP_NOFS);
        if (!req) {
                res = -ENOMEM;
                goto out;
        }
        skcipher_request_set_callback(req,
                        CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
                        crypto_req_done, &wait);
        res = crypto_skcipher_setkey(tfm, ctx->nonce, sizeof(ctx->nonce));
        if (res < 0)
                goto out;

        sg_init_one(&src_sg, master_key, derived_keysize);
        sg_init_one(&dst_sg, derived_key, derived_keysize);
        skcipher_request_set_crypt(req, &src_sg, &dst_sg, derived_keysize,
                                   NULL);
        res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
out:
        skcipher_request_free(req);
        crypto_free_skcipher(tfm);
        return res;
}

/*
 * Search the current task's subscribed keyrings for a "logon" key with
 * description prefix:descriptor, and if found acquire a read lock on it and
 * return a pointer to its validated payload in *payload_ret.
 */
static struct key *
find_and_lock_process_key(const char *prefix,
                          const u8 descriptor[FS_KEY_DESCRIPTOR_SIZE],
                          unsigned int min_keysize,
                          const struct fscrypt_key **payload_ret)
{
        char *description;
        struct key *key;
        const struct user_key_payload *ukp;
        const struct fscrypt_key *payload;

        description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
                                FS_KEY_DESCRIPTOR_SIZE, descriptor);
        if (!description)
                return ERR_PTR(-ENOMEM);

        key = request_key(&key_type_logon, description, NULL);
        kfree(description);
        if (IS_ERR(key))
                return key;

        down_read(&key->sem);
        ukp = user_key_payload_locked(key);

        if (!ukp) /* was the key revoked before we acquired its semaphore? */
                goto invalid;

        payload = (const struct fscrypt_key *)ukp->data;

        if (ukp->datalen != sizeof(struct fscrypt_key) ||
            payload->size < 1 || payload->size > FS_MAX_KEY_SIZE) {
                fscrypt_warn(NULL,
                             "key with description '%s' has invalid payload",
                             key->description);
                goto invalid;
        }

        if (payload->size < min_keysize) {
                fscrypt_warn(NULL,
                             "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
                             key->description, payload->size, min_keysize);
                goto invalid;
        }

        *payload_ret = payload;
        return key;

invalid:
        up_read(&key->sem);
        key_put(key);
        return ERR_PTR(-ENOKEY);
}

static struct fscrypt_mode available_modes[] = {
        [FS_ENCRYPTION_MODE_AES_256_XTS] = {
                .friendly_name = "AES-256-XTS",
                .cipher_str = "xts(aes)",
                .keysize = 64,
                .ivsize = 16,
        },
        [FS_ENCRYPTION_MODE_AES_256_CTS] = {
                .friendly_name = "AES-256-CTS-CBC",
                .cipher_str = "cts(cbc(aes))",
                .keysize = 32,
                .ivsize = 16,
        },
        [FS_ENCRYPTION_MODE_AES_128_CBC] = {
                .friendly_name = "AES-128-CBC",
                .cipher_str = "cbc(aes)",
                .keysize = 16,
                .ivsize = 16,
                .needs_essiv = true,
        },
        [FS_ENCRYPTION_MODE_AES_128_CTS] = {
                .friendly_name = "AES-128-CTS-CBC",
                .cipher_str = "cts(cbc(aes))",
                .keysize = 16,
                .ivsize = 16,
        },
        [FS_ENCRYPTION_MODE_ADIANTUM] = {
                .friendly_name = "Adiantum",
                .cipher_str = "adiantum(xchacha12,aes)",
                .keysize = 32,
                .ivsize = 32,
        },
};

static struct fscrypt_mode *
select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode)
{
        if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
                fscrypt_warn(inode->i_sb,
                             "inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)",
                             inode->i_ino, ci->ci_data_mode,
                             ci->ci_filename_mode);
                return ERR_PTR(-EINVAL);
        }

        if (S_ISREG(inode->i_mode))
                return &available_modes[ci->ci_data_mode];

        if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
                return &available_modes[ci->ci_filename_mode];

        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);
}

/* Find the master key, then derive the inode's actual encryption key */
static int find_and_derive_key(const struct inode *inode,
                               const struct fscrypt_context *ctx,
                               u8 *derived_key, const struct fscrypt_mode *mode)
{
        struct key *key;
        const struct fscrypt_key *payload;
        int err;

        key = find_and_lock_process_key(FS_KEY_DESC_PREFIX,
                                        ctx->master_key_descriptor,
                                        mode->keysize, &payload);
        if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) {
                key = find_and_lock_process_key(inode->i_sb->s_cop->key_prefix,
                                                ctx->master_key_descriptor,
                                                mode->keysize, &payload);
        }
        if (IS_ERR(key))
                return PTR_ERR(key);

        if (ctx->flags & FS_POLICY_FLAG_DIRECT_KEY) {
                if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
                        fscrypt_warn(inode->i_sb,
                                     "direct key mode not allowed with %s",
                                     mode->friendly_name);
                        err = -EINVAL;
                } else if (ctx->contents_encryption_mode !=
                           ctx->filenames_encryption_mode) {
                        fscrypt_warn(inode->i_sb,
                                     "direct key mode not allowed with different contents and filenames modes");
                        err = -EINVAL;
                } else {
                        memcpy(derived_key, payload->raw, mode->keysize);
                        err = 0;
                }
        } else {
                err = derive_key_aes(payload->raw, ctx, derived_key,
                                     mode->keysize);
        }
        up_read(&key->sem);
        key_put(key);
        return err;
}

/* Allocate and key a symmetric cipher object for the given encryption mode */
static struct crypto_skcipher *
allocate_skcipher_for_mode(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)) {
                fscrypt_warn(inode->i_sb,
                             "error allocating '%s' transform for inode %lu: %ld",
                             mode->cipher_str, inode->i_ino, PTR_ERR(tfm));
                return tfm;
        }
        if (unlikely(!mode->logged_impl_name)) {
                /*
                 * 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.  Note that multiple threads can
                 * race here, but it doesn't really matter.
                 */
                mode->logged_impl_name = true;
                pr_info("fscrypt: %s using implementation \"%s\"\n",
                        mode->friendly_name,
                        crypto_skcipher_alg(tfm)->base.cra_driver_name);
        }
        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);
}

/* Master key referenced by FS_POLICY_FLAG_DIRECT_KEY policy */
struct fscrypt_master_key {
        struct hlist_node mk_node;
        refcount_t mk_refcount;
        const struct fscrypt_mode *mk_mode;
        struct crypto_skcipher *mk_ctfm;
        u8 mk_descriptor[FS_KEY_DESCRIPTOR_SIZE];
        u8 mk_raw[FS_MAX_KEY_SIZE];
};

static void free_master_key(struct fscrypt_master_key *mk)
{
        if (mk) {
                crypto_free_skcipher(mk->mk_ctfm);
                kzfree(mk);
        }
}

static void put_master_key(struct fscrypt_master_key *mk)
{
        if (!refcount_dec_and_lock(&mk->mk_refcount, &fscrypt_master_keys_lock))
                return;
        hash_del(&mk->mk_node);
        spin_unlock(&fscrypt_master_keys_lock);

        free_master_key(mk);
}

/*
 * Find/insert the given master key into the fscrypt_master_keys table.  If
 * found, it is returned with elevated refcount, and 'to_insert' is freed if
 * non-NULL.  If not found, 'to_insert' is inserted and returned if it's
 * non-NULL; otherwise NULL is returned.
 */
static struct fscrypt_master_key *
find_or_insert_master_key(struct fscrypt_master_key *to_insert,
                          const u8 *raw_key, const struct fscrypt_mode *mode,
                          const struct fscrypt_info *ci)
{
        unsigned long hash_key;
        struct fscrypt_master_key *mk;

        /*
         * Careful: to avoid potentially leaking secret key bytes via timing
         * information, we must key the hash table by descriptor rather than by
         * raw key, and use crypto_memneq() when comparing raw keys.
         */

        BUILD_BUG_ON(sizeof(hash_key) > FS_KEY_DESCRIPTOR_SIZE);
        memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key));

        spin_lock(&fscrypt_master_keys_lock);
        hash_for_each_possible(fscrypt_master_keys, mk, mk_node, hash_key) {
                if (memcmp(ci->ci_master_key_descriptor, mk->mk_descriptor,
                           FS_KEY_DESCRIPTOR_SIZE) != 0)
                        continue;
                if (mode != mk->mk_mode)
                        continue;
                if (crypto_memneq(raw_key, mk->mk_raw, mode->keysize))
                        continue;
                /* using existing tfm with same (descriptor, mode, raw_key) */
                refcount_inc(&mk->mk_refcount);
                spin_unlock(&fscrypt_master_keys_lock);
                free_master_key(to_insert);
                return mk;
        }
        if (to_insert)
                hash_add(fscrypt_master_keys, &to_insert->mk_node, hash_key);
        spin_unlock(&fscrypt_master_keys_lock);
        return to_insert;
}

/* Prepare to encrypt directly using the master key in the given mode */
static struct fscrypt_master_key *
fscrypt_get_master_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
                       const u8 *raw_key, const struct inode *inode)
{
        struct fscrypt_master_key *mk;
        int err;

        /* Is there already a tfm for this key? */
        mk = find_or_insert_master_key(NULL, raw_key, mode, ci);
        if (mk)
                return mk;

        /* Nope, allocate one. */
        mk = kzalloc(sizeof(*mk), GFP_NOFS);
        if (!mk)
                return ERR_PTR(-ENOMEM);
        refcount_set(&mk->mk_refcount, 1);
        mk->mk_mode = mode;
        mk->mk_ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
        if (IS_ERR(mk->mk_ctfm)) {
                err = PTR_ERR(mk->mk_ctfm);
                mk->mk_ctfm = NULL;
                goto err_free_mk;
        }
        memcpy(mk->mk_descriptor, ci->ci_master_key_descriptor,
               FS_KEY_DESCRIPTOR_SIZE);
        memcpy(mk->mk_raw, raw_key, mode->keysize);

        return find_or_insert_master_key(mk, raw_key, mode, ci);

err_free_mk:
        free_master_key(mk);
        return ERR_PTR(err);
}

static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
{
        struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);

        /* init hash transform on demand */
        if (unlikely(!tfm)) {
                struct crypto_shash *prev_tfm;

                tfm = crypto_alloc_shash("sha256", 0, 0);
                if (IS_ERR(tfm)) {
                        fscrypt_warn(NULL,
                                     "error allocating SHA-256 transform: %ld",
                                     PTR_ERR(tfm));
                        return PTR_ERR(tfm);
                }
                prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
                if (prev_tfm) {
                        crypto_free_shash(tfm);
                        tfm = prev_tfm;
                }
        }

        {
                SHASH_DESC_ON_STACK(desc, tfm);
                desc->tfm = tfm;

                return crypto_shash_digest(desc, key, keysize, salt);
        }
}

static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
                                int keysize)
{
        int err;
        struct crypto_cipher *essiv_tfm;
        u8 salt[SHA256_DIGEST_SIZE];

        essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
        if (IS_ERR(essiv_tfm))
                return PTR_ERR(essiv_tfm);

        ci->ci_essiv_tfm = essiv_tfm;

        err = derive_essiv_salt(raw_key, keysize, salt);
        if (err)
                goto out;

        /*
         * Using SHA256 to derive the salt/key will result in AES-256 being
         * used for IV generation. File contents encryption will still use the
         * configured keysize (AES-128) nevertheless.
         */
        err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
        if (err)
                goto out;

out:
        memzero_explicit(salt, sizeof(salt));
        return err;
}

void __exit fscrypt_essiv_cleanup(void)
{
        crypto_free_shash(essiv_hash_tfm);
}

/*
 * Given the encryption mode and key (normally the derived key, but for
 * FS_POLICY_FLAG_DIRECT_KEY mode it's the master key), set up the inode's
 * symmetric cipher transform object(s).
 */
static int setup_crypto_transform(struct fscrypt_info *ci,
                                  struct fscrypt_mode *mode,
                                  const u8 *raw_key, const struct inode *inode)
{
        struct fscrypt_master_key *mk;
        struct crypto_skcipher *ctfm;
        int err;

        if (ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY) {
                mk = fscrypt_get_master_key(ci, mode, raw_key, inode);
                if (IS_ERR(mk))
                        return PTR_ERR(mk);
                ctfm = mk->mk_ctfm;
        } else {
                mk = NULL;
                ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
                if (IS_ERR(ctfm))
                        return PTR_ERR(ctfm);
        }
        ci->ci_master_key = mk;
        ci->ci_ctfm = ctfm;

        if (mode->needs_essiv) {
                /* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
                WARN_ON(mode->ivsize != AES_BLOCK_SIZE);
                WARN_ON(ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY);

                err = init_essiv_generator(ci, raw_key, mode->keysize);
                if (err) {
                        fscrypt_warn(inode->i_sb,
                                     "error initializing ESSIV generator for inode %lu: %d",
                                     inode->i_ino, err);
                        return err;
                }
        }
        return 0;
}

static void put_crypt_info(struct fscrypt_info *ci)
{
        if (!ci)
                return;

        if (ci->ci_master_key) {
                put_master_key(ci->ci_master_key);
        } else {
                crypto_free_skcipher(ci->ci_ctfm);
                crypto_free_cipher(ci->ci_essiv_tfm);
        }
        kmem_cache_free(fscrypt_info_cachep, ci);
}

int fscrypt_get_encryption_info(struct inode *inode)
{
        struct fscrypt_info *crypt_info;
        struct fscrypt_context ctx;
        struct fscrypt_mode *mode;
        u8 *raw_key = NULL;
        int res;

        if (fscrypt_has_encryption_key(inode))
                return 0;

        res = fscrypt_initialize(inode->i_sb->s_cop->flags);
        if (res)
                return res;

        res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
        if (res < 0) {
                if (!fscrypt_dummy_context_enabled(inode) ||
                    IS_ENCRYPTED(inode))
                        return res;
                /* Fake up a context for an unencrypted directory */
                memset(&ctx, 0, sizeof(ctx));
                ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
                ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
                ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
                memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
        } else if (res != sizeof(ctx)) {
                return -EINVAL;
        }

        if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
                return -EINVAL;

        if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
                return -EINVAL;

        crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
        if (!crypt_info)
                return -ENOMEM;

        crypt_info->ci_flags = ctx.flags;
        crypt_info->ci_data_mode = ctx.contents_encryption_mode;
        crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
        memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
               FS_KEY_DESCRIPTOR_SIZE);
        memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);

        mode = select_encryption_mode(crypt_info, inode);
        if (IS_ERR(mode)) {
                res = PTR_ERR(mode);
                goto out;
        }
        WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
        crypt_info->ci_mode = mode;

        /*
         * This cannot be a stack buffer because it may be passed to the
         * scatterlist crypto API as part of key derivation.
         */
        res = -ENOMEM;
        raw_key = kmalloc(mode->keysize, GFP_NOFS);
        if (!raw_key)
                goto out;

        res = find_and_derive_key(inode, &ctx, raw_key, mode);
        if (res)
                goto out;

        res = setup_crypto_transform(crypt_info, mode, raw_key, inode);
        if (res)
                goto out;

        if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL)
                crypt_info = NULL;
out:
        if (res == -ENOKEY)
                res = 0;
        put_crypt_info(crypt_info);
        kzfree(raw_key);
        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);