diff options
| -rw-r--r-- | fs/crypto/fscrypt_private.h | 53 | ||||
| -rw-r--r-- | fs/crypto/keyring.c | 260 | ||||
| -rw-r--r-- | fs/crypto/keysetup.c | 103 | ||||
| -rw-r--r-- | include/linux/fscrypt.h | 12 | ||||
| -rw-r--r-- | include/uapi/linux/fscrypt.h | 9 |
5 files changed, 432 insertions, 5 deletions
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h index 0d9ebfd3bf3a..fc804f4a03fc 100644 --- a/fs/crypto/fscrypt_private.h +++ b/fs/crypto/fscrypt_private.h @@ -79,6 +79,19 @@ struct fscrypt_info { struct inode *ci_inode; /* + * The master key with which this inode was unlocked (decrypted). This + * will be NULL if the master key was found in a process-subscribed + * keyring rather than in the filesystem-level keyring. + */ + struct key *ci_master_key; + + /* + * Link in list of inodes that were unlocked with the master key. + * Only used when ->ci_master_key is set. + */ + struct list_head ci_master_key_link; + + /* * If non-NULL, then encryption is done using the master key directly * and ci_ctfm will equal ci_direct_key->dk_ctfm. */ @@ -183,14 +196,52 @@ struct fscrypt_master_key_secret { */ struct fscrypt_master_key { - /* The secret key material */ + /* + * The secret key material. After FS_IOC_REMOVE_ENCRYPTION_KEY is + * executed, this is wiped and no new inodes can be unlocked with this + * key; however, there may still be inodes in ->mk_decrypted_inodes + * which could not be evicted. As long as some inodes still remain, + * FS_IOC_REMOVE_ENCRYPTION_KEY can be retried, or + * FS_IOC_ADD_ENCRYPTION_KEY can add the secret again. + * + * Locking: protected by key->sem. + */ struct fscrypt_master_key_secret mk_secret; /* Arbitrary key descriptor which was assigned by userspace */ struct fscrypt_key_specifier mk_spec; + /* + * Length of ->mk_decrypted_inodes, plus one if mk_secret is present. + * Once this goes to 0, the master key is removed from ->s_master_keys. + * The 'struct fscrypt_master_key' will continue to live as long as the + * 'struct key' whose payload it is, but we won't let this reference + * count rise again. + */ + refcount_t mk_refcount; + + /* + * List of inodes that were unlocked using this key. This allows the + * inodes to be evicted efficiently if the key is removed. + */ + struct list_head mk_decrypted_inodes; + spinlock_t mk_decrypted_inodes_lock; + } __randomize_layout; +static inline bool +is_master_key_secret_present(const struct fscrypt_master_key_secret *secret) +{ + /* + * The READ_ONCE() is only necessary for fscrypt_drop_inode() and + * fscrypt_key_describe(). These run in atomic context, so they can't + * take key->sem and thus 'secret' can change concurrently which would + * be a data race. But they only need to know whether the secret *was* + * present at the time of check, so READ_ONCE() suffices. + */ + return READ_ONCE(secret->size) != 0; +} + static inline const char *master_key_spec_type( const struct fscrypt_key_specifier *spec) { diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c index bcd7d2836e1e..c3423f0edc70 100644 --- a/fs/crypto/keyring.c +++ b/fs/crypto/keyring.c @@ -10,6 +10,7 @@ * filesystem-level keyring, including the ioctls: * * - FS_IOC_ADD_ENCRYPTION_KEY + * - FS_IOC_REMOVE_ENCRYPTION_KEY * * See the "User API" section of Documentation/filesystems/fscrypt.rst for more * information about these ioctls. @@ -60,6 +61,13 @@ static void fscrypt_key_destroy(struct key *key) static void fscrypt_key_describe(const struct key *key, struct seq_file *m) { seq_puts(m, key->description); + + if (key_is_positive(key)) { + const struct fscrypt_master_key *mk = key->payload.data[0]; + + if (!is_master_key_secret_present(&mk->mk_secret)) + seq_puts(m, ": secret removed"); + } } /* @@ -186,6 +194,10 @@ static int add_new_master_key(struct fscrypt_master_key_secret *secret, move_master_key_secret(&mk->mk_secret, secret); + refcount_set(&mk->mk_refcount, 1); /* secret is present */ + INIT_LIST_HEAD(&mk->mk_decrypted_inodes); + spin_lock_init(&mk->mk_decrypted_inodes_lock); + format_mk_description(description, mk_spec); key = key_alloc(&key_type_fscrypt, description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(), @@ -207,6 +219,21 @@ out_free_mk: return err; } +#define KEY_DEAD 1 + +static int add_existing_master_key(struct fscrypt_master_key *mk, + struct fscrypt_master_key_secret *secret) +{ + if (is_master_key_secret_present(&mk->mk_secret)) + return 0; + + if (!refcount_inc_not_zero(&mk->mk_refcount)) + return KEY_DEAD; + + move_master_key_secret(&mk->mk_secret, secret); + return 0; +} + static int add_master_key(struct super_block *sb, struct fscrypt_master_key_secret *secret, const struct fscrypt_key_specifier *mk_spec) @@ -216,6 +243,7 @@ static int add_master_key(struct super_block *sb, int err; mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */ +retry: key = fscrypt_find_master_key(sb, mk_spec); if (IS_ERR(key)) { err = PTR_ERR(key); @@ -227,8 +255,20 @@ static int add_master_key(struct super_block *sb, goto out_unlock; err = add_new_master_key(secret, mk_spec, sb->s_master_keys); } else { + /* + * Found the key in ->s_master_keys. Re-add the secret if + * needed. + */ + down_write(&key->sem); + err = add_existing_master_key(key->payload.data[0], secret); + up_write(&key->sem); + if (err == KEY_DEAD) { + /* Key being removed or needs to be removed */ + key_invalidate(key); + key_put(key); + goto retry; + } key_put(key); - err = 0; } out_unlock: mutex_unlock(&fscrypt_add_key_mutex); @@ -280,6 +320,224 @@ out_wipe_secret: } EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key); +/* + * Try to evict the inode's dentries from the dentry cache. If the inode is a + * directory, then it can have at most one dentry; however, that dentry may be + * pinned by child dentries, so first try to evict the children too. + */ +static void shrink_dcache_inode(struct inode *inode) +{ + struct dentry *dentry; + + if (S_ISDIR(inode->i_mode)) { + dentry = d_find_any_alias(inode); + if (dentry) { + shrink_dcache_parent(dentry); + dput(dentry); + } + } + d_prune_aliases(inode); +} + +static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk) +{ + struct fscrypt_info *ci; + struct inode *inode; + struct inode *toput_inode = NULL; + + spin_lock(&mk->mk_decrypted_inodes_lock); + + list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) { + inode = ci->ci_inode; + spin_lock(&inode->i_lock); + if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) { + spin_unlock(&inode->i_lock); + continue; + } + __iget(inode); + spin_unlock(&inode->i_lock); + spin_unlock(&mk->mk_decrypted_inodes_lock); + + shrink_dcache_inode(inode); + iput(toput_inode); + toput_inode = inode; + + spin_lock(&mk->mk_decrypted_inodes_lock); + } + + spin_unlock(&mk->mk_decrypted_inodes_lock); + iput(toput_inode); +} + +static int check_for_busy_inodes(struct super_block *sb, + struct fscrypt_master_key *mk) +{ + struct list_head *pos; + size_t busy_count = 0; + unsigned long ino; + struct dentry *dentry; + char _path[256]; + char *path = NULL; + + spin_lock(&mk->mk_decrypted_inodes_lock); + + list_for_each(pos, &mk->mk_decrypted_inodes) + busy_count++; + + if (busy_count == 0) { + spin_unlock(&mk->mk_decrypted_inodes_lock); + return 0; + } + + { + /* select an example file to show for debugging purposes */ + struct inode *inode = + list_first_entry(&mk->mk_decrypted_inodes, + struct fscrypt_info, + ci_master_key_link)->ci_inode; + ino = inode->i_ino; + dentry = d_find_alias(inode); + } + spin_unlock(&mk->mk_decrypted_inodes_lock); + + if (dentry) { + path = dentry_path(dentry, _path, sizeof(_path)); + dput(dentry); + } + if (IS_ERR_OR_NULL(path)) + path = "(unknown)"; + + fscrypt_warn(NULL, + "%s: %zu inode(s) still busy after removing key with %s %*phN, including ino %lu (%s)", + sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec), + master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u, + ino, path); + return -EBUSY; +} + +static int try_to_lock_encrypted_files(struct super_block *sb, + struct fscrypt_master_key *mk) +{ + int err1; + int err2; + + /* + * An inode can't be evicted while it is dirty or has dirty pages. + * Thus, we first have to clean the inodes in ->mk_decrypted_inodes. + * + * Just do it the easy way: call sync_filesystem(). It's overkill, but + * it works, and it's more important to minimize the amount of caches we + * drop than the amount of data we sync. Also, unprivileged users can + * already call sync_filesystem() via sys_syncfs() or sys_sync(). + */ + down_read(&sb->s_umount); + err1 = sync_filesystem(sb); + up_read(&sb->s_umount); + /* If a sync error occurs, still try to evict as much as possible. */ + + /* + * Inodes are pinned by their dentries, so we have to evict their + * dentries. shrink_dcache_sb() would suffice, but would be overkill + * and inappropriate for use by unprivileged users. So instead go + * through the inodes' alias lists and try to evict each dentry. + */ + evict_dentries_for_decrypted_inodes(mk); + + /* + * evict_dentries_for_decrypted_inodes() already iput() each inode in + * the list; any inodes for which that dropped the last reference will + * have been evicted due to fscrypt_drop_inode() detecting the key + * removal and telling the VFS to evict the inode. So to finish, we + * just need to check whether any inodes couldn't be evicted. + */ + err2 = check_for_busy_inodes(sb, mk); + + return err1 ?: err2; +} + +/* + * Try to remove an fscrypt master encryption key. + * + * First we wipe the actual master key secret, so that no more inodes can be + * unlocked with it. Then we try to evict all cached inodes that had been + * unlocked with the key. + * + * If all inodes were evicted, then we unlink the fscrypt_master_key from the + * keyring. Otherwise it remains in the keyring in the "incompletely removed" + * state (without the actual secret key) where it tracks the list of remaining + * inodes. Userspace can execute the ioctl again later to retry eviction, or + * alternatively can re-add the secret key again. + * + * For more details, see the "Removing keys" section of + * Documentation/filesystems/fscrypt.rst. + */ +int fscrypt_ioctl_remove_key(struct file *filp, void __user *_uarg) +{ + struct super_block *sb = file_inode(filp)->i_sb; + struct fscrypt_remove_key_arg __user *uarg = _uarg; + struct fscrypt_remove_key_arg arg; + struct key *key; + struct fscrypt_master_key *mk; + u32 status_flags = 0; + int err; + bool dead; + + if (copy_from_user(&arg, uarg, sizeof(arg))) + return -EFAULT; + + if (!valid_key_spec(&arg.key_spec)) + return -EINVAL; + + if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved))) + return -EINVAL; + + if (!capable(CAP_SYS_ADMIN)) + return -EACCES; + + /* Find the key being removed. */ + key = fscrypt_find_master_key(sb, &arg.key_spec); + if (IS_ERR(key)) + return PTR_ERR(key); + mk = key->payload.data[0]; + + down_write(&key->sem); + + /* Wipe the secret. */ + dead = false; + if (is_master_key_secret_present(&mk->mk_secret)) { + wipe_master_key_secret(&mk->mk_secret); + dead = refcount_dec_and_test(&mk->mk_refcount); + } + up_write(&key->sem); + if (dead) { + /* + * No inodes reference the key, and we wiped the secret, so the + * key object is free to be removed from the keyring. + */ + key_invalidate(key); + err = 0; + } else { + /* Some inodes still reference this key; try to evict them. */ + err = try_to_lock_encrypted_files(sb, mk); + if (err == -EBUSY) { + status_flags |= + FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY; + err = 0; + } + } + /* + * We return 0 if we successfully did something: wiped the secret, or + * tried locking the files again. Users need to check the informational + * status flags if they care whether the key has been fully removed + * including all files locked. + */ + key_put(key); + if (err == 0) + err = put_user(status_flags, &uarg->removal_status_flags); + return err; +} +EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key); + int __init fscrypt_init_keyring(void) { return register_key_type(&key_type_fscrypt); diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c index 1c6d18bcdc7b..7b60a47fc73c 100644 --- a/fs/crypto/keysetup.c +++ b/fs/crypto/keysetup.c @@ -213,8 +213,16 @@ int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key) /* * 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 the + * corresponding 'struct key' is returned in *master_key_ret with + * ->sem read-locked. This is needed to ensure that only one task links the + * fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race to create + * an fscrypt_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_info *ci) +static int setup_file_encryption_key(struct fscrypt_info *ci, + struct key **master_key_ret) { struct key *key; struct fscrypt_master_key *mk = NULL; @@ -234,6 +242,13 @@ static int setup_file_encryption_key(struct fscrypt_info *ci) } mk = key->payload.data[0]; + down_read(&key->sem); + + /* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */ + if (!is_master_key_secret_present(&mk->mk_secret)) { + err = -ENOKEY; + goto out_release_key; + } if (mk->mk_secret.size < ci->ci_mode->keysize) { fscrypt_warn(NULL, @@ -246,14 +261,22 @@ static int setup_file_encryption_key(struct fscrypt_info *ci) } err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw); + if (err) + goto out_release_key; + + *master_key_ret = key; + return 0; out_release_key: + up_read(&key->sem); key_put(key); return err; } static void put_crypt_info(struct fscrypt_info *ci) { + struct key *key; + if (!ci) return; @@ -263,6 +286,26 @@ static void put_crypt_info(struct fscrypt_info *ci) crypto_free_skcipher(ci->ci_ctfm); crypto_free_cipher(ci->ci_essiv_tfm); } + + key = ci->ci_master_key; + if (key) { + struct fscrypt_master_key *mk = key->payload.data[0]; + + /* + * 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 a key that + * already had its secret removed, invalidate the key so that it + * gets removed from ->s_master_keys. + */ + spin_lock(&mk->mk_decrypted_inodes_lock); + list_del(&ci->ci_master_key_link); + spin_unlock(&mk->mk_decrypted_inodes_lock); + if (refcount_dec_and_test(&mk->mk_refcount)) + key_invalidate(key); + key_put(key); + } kmem_cache_free(fscrypt_info_cachep, ci); } @@ -271,6 +314,7 @@ int fscrypt_get_encryption_info(struct inode *inode) struct fscrypt_info *crypt_info; struct fscrypt_context ctx; struct fscrypt_mode *mode; + struct key *master_key = NULL; int res; if (fscrypt_has_encryption_key(inode)) @@ -335,13 +379,30 @@ int fscrypt_get_encryption_info(struct inode *inode) WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE); crypt_info->ci_mode = mode; - res = setup_file_encryption_key(crypt_info); + 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 (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) { + up_read(&master_key->sem); + key_put(master_key); + } if (res == -ENOKEY) res = 0; put_crypt_info(crypt_info); @@ -376,3 +437,39 @@ void fscrypt_free_inode(struct inode *inode) } } 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]; + + /* + * Note: since we aren't holding key->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); diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index 46bf66cf76ef..b494c5f9c01f 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -141,11 +141,13 @@ extern int fscrypt_inherit_context(struct inode *, struct inode *, /* keyring.c */ extern void fscrypt_sb_free(struct super_block *sb); extern int fscrypt_ioctl_add_key(struct file *filp, void __user *arg); +extern int fscrypt_ioctl_remove_key(struct file *filp, void __user *arg); /* keysetup.c */ extern int fscrypt_get_encryption_info(struct inode *); extern void fscrypt_put_encryption_info(struct inode *); extern void fscrypt_free_inode(struct inode *); +extern int fscrypt_drop_inode(struct inode *inode); /* fname.c */ extern int fscrypt_setup_filename(struct inode *, const struct qstr *, @@ -381,6 +383,11 @@ static inline int fscrypt_ioctl_add_key(struct file *filp, void __user *arg) return -EOPNOTSUPP; } +static inline int fscrypt_ioctl_remove_key(struct file *filp, void __user *arg) +{ + return -EOPNOTSUPP; +} + /* keysetup.c */ static inline int fscrypt_get_encryption_info(struct inode *inode) { @@ -396,6 +403,11 @@ static inline void fscrypt_free_inode(struct inode *inode) { } +static inline int fscrypt_drop_inode(struct inode *inode) +{ + return 0; +} + /* fname.c */ static inline int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname, diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h index 6aeca3cb0a2d..07f37a27a944 100644 --- a/include/uapi/linux/fscrypt.h +++ b/include/uapi/linux/fscrypt.h @@ -76,10 +76,19 @@ struct fscrypt_add_key_arg { __u8 raw[]; }; +/* Struct passed to FS_IOC_REMOVE_ENCRYPTION_KEY */ +struct fscrypt_remove_key_arg { + struct fscrypt_key_specifier key_spec; +#define FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY 0x00000001 + __u32 removal_status_flags; /* output */ + __u32 __reserved[5]; +}; + #define FS_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct fscrypt_policy) #define FS_IOC_GET_ENCRYPTION_PWSALT _IOW('f', 20, __u8[16]) #define FS_IOC_GET_ENCRYPTION_POLICY _IOW('f', 21, struct fscrypt_policy) #define FS_IOC_ADD_ENCRYPTION_KEY _IOWR('f', 23, struct fscrypt_add_key_arg) +#define FS_IOC_REMOVE_ENCRYPTION_KEY _IOWR('f', 24, struct fscrypt_remove_key_arg) /**********************************************************************/ |