// SPDX-License-Identifier: GPL-2.0-or-later /* Large capacity key type * * Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com) */ #define pr_fmt(fmt) "big_key: "fmt #include <linux/init.h> #include <linux/seq_file.h> #include <linux/file.h> #include <linux/shmem_fs.h> #include <linux/err.h> #include <linux/scatterlist.h> #include <linux/random.h> #include <linux/vmalloc.h> #include <keys/user-type.h> #include <keys/big_key-type.h> #include <crypto/aead.h> #include <crypto/gcm.h> struct big_key_buf { unsigned int nr_pages; void *virt; struct scatterlist *sg; struct page *pages[]; }; /* * Layout of key payload words. */ enum { big_key_data, big_key_path, big_key_path_2nd_part, big_key_len, }; /* * Crypto operation with big_key data */ enum big_key_op { BIG_KEY_ENC, BIG_KEY_DEC, }; /* * If the data is under this limit, there's no point creating a shm file to * hold it as the permanently resident metadata for the shmem fs will be at * least as large as the data. */ #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry)) /* * Key size for big_key data encryption */ #define ENC_KEY_SIZE 32 /* * Authentication tag length */ #define ENC_AUTHTAG_SIZE 16 /* * big_key defined keys take an arbitrary string as the description and an * arbitrary blob of data as the payload */ struct key_type key_type_big_key = { .name = "big_key", .preparse = big_key_preparse, .free_preparse = big_key_free_preparse, .instantiate = generic_key_instantiate, .revoke = big_key_revoke, .destroy = big_key_destroy, .describe = big_key_describe, .read = big_key_read, /* no ->update(); don't add it without changing big_key_crypt() nonce */ }; /* * Crypto names for big_key data authenticated encryption */ static const char big_key_alg_name[] = "gcm(aes)"; #define BIG_KEY_IV_SIZE GCM_AES_IV_SIZE /* * Crypto algorithms for big_key data authenticated encryption */ static struct crypto_aead *big_key_aead; /* * Since changing the key affects the entire object, we need a mutex. */ static DEFINE_MUTEX(big_key_aead_lock); /* * Encrypt/decrypt big_key data */ static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t datalen, u8 *key) { int ret; struct aead_request *aead_req; /* We always use a zero nonce. The reason we can get away with this is * because we're using a different randomly generated key for every * different encryption. Notably, too, key_type_big_key doesn't define * an .update function, so there's no chance we'll wind up reusing the * key to encrypt updated data. Simply put: one key, one encryption. */ u8 zero_nonce[BIG_KEY_IV_SIZE]; aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL); if (!aead_req) return -ENOMEM; memset(zero_nonce, 0, sizeof(zero_nonce)); aead_request_set_crypt(aead_req, buf->sg, buf->sg, datalen, zero_nonce); aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL); aead_request_set_ad(aead_req, 0); mutex_lock(&big_key_aead_lock); if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) { ret = -EAGAIN; goto error; } if (op == BIG_KEY_ENC) ret = crypto_aead_encrypt(aead_req); else ret = crypto_aead_decrypt(aead_req); error: mutex_unlock(&big_key_aead_lock); aead_request_free(aead_req); return ret; } /* * Free up the buffer. */ static void big_key_free_buffer(struct big_key_buf *buf) { unsigned int i; if (buf->virt) { memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE); vunmap(buf->virt); } for (i = 0; i < buf->nr_pages; i++) if (buf->pages[i]) __free_page(buf->pages[i]); kfree(buf); } /* * Allocate a buffer consisting of a set of pages with a virtual mapping * applied over them. */ static void *big_key_alloc_buffer(size_t len) { struct big_key_buf *buf; unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT; unsigned int i, l; buf = kzalloc(sizeof(struct big_key_buf) + sizeof(struct page) * npg + sizeof(struct scatterlist) * npg, GFP_KERNEL); if (!buf) return NULL; buf->nr_pages = npg; buf->sg = (void *)(buf->pages + npg); sg_init_table(buf->sg, npg); for (i = 0; i < buf->nr_pages; i++) { buf->pages[i] = alloc_page(GFP_KERNEL); if (!buf->pages[i]) goto nomem; l = min_t(size_t, len, PAGE_SIZE); sg_set_page(&buf->sg[i], buf->pages[i], l, 0); len -= l; } buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL); if (!buf->virt) goto nomem; return buf; nomem: big_key_free_buffer(buf); return NULL; } /* * Preparse a big key */ int big_key_preparse(struct key_preparsed_payload *prep) { struct big_key_buf *buf; struct path *path = (struct path *)&prep->payload.data[big_key_path]; struct file *file; u8 *enckey; ssize_t written; size_t datalen = prep->datalen, enclen = datalen + ENC_AUTHTAG_SIZE; int ret; if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data) return -EINVAL; /* Set an arbitrary quota */ prep->quotalen = 16; prep->payload.data[big_key_len] = (void *)(unsigned long)datalen; if (datalen > BIG_KEY_FILE_THRESHOLD) { /* Create a shmem file to store the data in. This will permit the data * to be swapped out if needed. * * File content is stored encrypted with randomly generated key. */ loff_t pos = 0; buf = big_key_alloc_buffer(enclen); if (!buf) return -ENOMEM; memcpy(buf->virt, prep->data, datalen); /* generate random key */ enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL); if (!enckey) { ret = -ENOMEM; goto error; } ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE); if (unlikely(ret)) goto err_enckey; /* encrypt aligned data */ ret = big_key_crypt(BIG_KEY_ENC, buf, datalen, enckey); if (ret) goto err_enckey; /* save aligned data to file */ file = shmem_kernel_file_setup("", enclen, 0); if (IS_ERR(file)) { ret = PTR_ERR(file); goto err_enckey; } written = kernel_write(file, buf->virt, enclen, &pos); if (written != enclen) { ret = written; if (written >= 0) ret = -ENOMEM; goto err_fput; } /* Pin the mount and dentry to the key so that we can open it again * later */ prep->payload.data[big_key_data] = enckey; *path = file->f_path; path_get(path); fput(file); big_key_free_buffer(buf); } else { /* Just store the data in a buffer */ void *data = kmalloc(datalen, GFP_KERNEL); if (!data) return -ENOMEM; prep->payload.data[big_key_data] = data; memcpy(data, prep->data, prep->datalen); } return 0; err_fput: fput(file); err_enckey: kzfree(enckey); error: big_key_free_buffer(buf); return ret; } /* * Clear preparsement. */ void big_key_free_preparse(struct key_preparsed_payload *prep) { if (prep->datalen > BIG_KEY_FILE_THRESHOLD) { struct path *path = (struct path *)&prep->payload.data[big_key_path]; path_put(path); } kzfree(prep->payload.data[big_key_data]); } /* * dispose of the links from a revoked keyring * - called with the key sem write-locked */ void big_key_revoke(struct key *key) { struct path *path = (struct path *)&key->payload.data[big_key_path]; /* clear the quota */ key_payload_reserve(key, 0); if (key_is_positive(key) && (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD) vfs_truncate(path, 0); } /* * dispose of the data dangling from the corpse of a big_key key */ void big_key_destroy(struct key *key) { size_t datalen = (size_t)key->payload.data[big_key_len]; if (datalen > BIG_KEY_FILE_THRESHOLD) { struct path *path = (struct path *)&key->payload.data[big_key_path]; path_put(path); path->mnt = NULL; path->dentry = NULL; } kzfree(key->payload.data[big_key_data]); key->payload.data[big_key_data] = NULL; } /* * describe the big_key key */ void big_key_describe(const struct key *key, struct seq_file *m) { size_t datalen = (size_t)key->payload.data[big_key_len]; seq_puts(m, key->description); if (key_is_positive(key)) seq_printf(m, ": %zu [%s]", datalen, datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff"); } /* * read the key data * - the key's semaphore is read-locked */ long big_key_read(const struct key *key, char __user *buffer, size_t buflen) { size_t datalen = (size_t)key->payload.data[big_key_len]; long ret; if (!buffer || buflen < datalen) return datalen; if (datalen > BIG_KEY_FILE_THRESHOLD) { struct big_key_buf *buf; struct path *path = (struct path *)&key->payload.data[big_key_path]; struct file *file; u8 *enckey = (u8 *)key->payload.data[big_key_data]; size_t enclen = datalen + ENC_AUTHTAG_SIZE; loff_t pos = 0; buf = big_key_alloc_buffer(enclen); if (!buf) return -ENOMEM; file = dentry_open(path, O_RDONLY, current_cred()); if (IS_ERR(file)) { ret = PTR_ERR(file); goto error; } /* read file to kernel and decrypt */ ret = kernel_read(file, buf->virt, enclen, &pos); if (ret >= 0 && ret != enclen) { ret = -EIO; goto err_fput; } ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey); if (ret) goto err_fput; ret = datalen; /* copy decrypted data to user */ if (copy_to_user(buffer, buf->virt, datalen) != 0) ret = -EFAULT; err_fput: fput(file); error: big_key_free_buffer(buf); } else { ret = datalen; if (copy_to_user(buffer, key->payload.data[big_key_data], datalen) != 0) ret = -EFAULT; } return ret; } /* * Register key type */ static int __init big_key_init(void) { int ret; /* init block cipher */ big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC); if (IS_ERR(big_key_aead)) { ret = PTR_ERR(big_key_aead); pr_err("Can't alloc crypto: %d\n", ret); return ret; } if (unlikely(crypto_aead_ivsize(big_key_aead) != BIG_KEY_IV_SIZE)) { WARN(1, "big key algorithm changed?"); ret = -EINVAL; goto free_aead; } ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE); if (ret < 0) { pr_err("Can't set crypto auth tag len: %d\n", ret); goto free_aead; } ret = register_key_type(&key_type_big_key); if (ret < 0) { pr_err("Can't register type: %d\n", ret); goto free_aead; } return 0; free_aead: crypto_free_aead(big_key_aead); return ret; } late_initcall(big_key_init);