// SPDX-License-Identifier: GPL-2.0 /* * Encryption policy functions for per-file encryption support. * * Copyright (C) 2015, Google, Inc. * Copyright (C) 2015, Motorola Mobility. * * Written by Michael Halcrow, 2015. * Modified by Jaegeuk Kim, 2015. */ #include <linux/random.h> #include <linux/string.h> #include <linux/mount.h> #include "fscrypt_private.h" /* * check whether an encryption policy is consistent with an encryption context */ static bool is_encryption_context_consistent_with_policy( const struct fscrypt_context *ctx, const struct fscrypt_policy *policy) { return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE) == 0 && (ctx->flags == policy->flags) && (ctx->contents_encryption_mode == policy->contents_encryption_mode) && (ctx->filenames_encryption_mode == policy->filenames_encryption_mode); } static int create_encryption_context_from_policy(struct inode *inode, const struct fscrypt_policy *policy) { struct fscrypt_context ctx; ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1; memcpy(ctx.master_key_descriptor, policy->master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE); if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode, policy->filenames_encryption_mode)) return -EINVAL; if (policy->flags & ~FS_POLICY_FLAGS_VALID) return -EINVAL; ctx.contents_encryption_mode = policy->contents_encryption_mode; ctx.filenames_encryption_mode = policy->filenames_encryption_mode; ctx.flags = policy->flags; BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE); get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE); return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL); } int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg) { struct fscrypt_policy policy; struct inode *inode = file_inode(filp); int ret; struct fscrypt_context ctx; if (copy_from_user(&policy, arg, sizeof(policy))) return -EFAULT; if (!inode_owner_or_capable(inode)) return -EACCES; if (policy.version != 0) return -EINVAL; ret = mnt_want_write_file(filp); if (ret) return ret; inode_lock(inode); ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx)); if (ret == -ENODATA) { if (!S_ISDIR(inode->i_mode)) ret = -ENOTDIR; else if (!inode->i_sb->s_cop->empty_dir(inode)) ret = -ENOTEMPTY; else ret = create_encryption_context_from_policy(inode, &policy); } else if (ret == sizeof(ctx) && is_encryption_context_consistent_with_policy(&ctx, &policy)) { /* The file already uses the same encryption policy. */ ret = 0; } else if (ret >= 0 || ret == -ERANGE) { /* The file already uses a different encryption policy. */ ret = -EEXIST; } inode_unlock(inode); mnt_drop_write_file(filp); return ret; } EXPORT_SYMBOL(fscrypt_ioctl_set_policy); int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg) { struct inode *inode = file_inode(filp); struct fscrypt_context ctx; struct fscrypt_policy policy; int res; if (!IS_ENCRYPTED(inode)) return -ENODATA; res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx)); if (res < 0 && res != -ERANGE) return res; if (res != sizeof(ctx)) return -EINVAL; if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1) return -EINVAL; policy.version = 0; policy.contents_encryption_mode = ctx.contents_encryption_mode; policy.filenames_encryption_mode = ctx.filenames_encryption_mode; policy.flags = ctx.flags; memcpy(policy.master_key_descriptor, ctx.master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE); if (copy_to_user(arg, &policy, sizeof(policy))) return -EFAULT; return 0; } EXPORT_SYMBOL(fscrypt_ioctl_get_policy); /** * fscrypt_has_permitted_context() - is a file's encryption policy permitted * within its directory? * * @parent: inode for parent directory * @child: inode for file being looked up, opened, or linked into @parent * * Filesystems must call this before permitting access to an inode in a * situation where the parent directory is encrypted (either before allowing * ->lookup() to succeed, or for a regular file before allowing it to be opened) * and before any operation that involves linking an inode into an encrypted * directory, including link, rename, and cross rename. It enforces the * constraint that within a given encrypted directory tree, all files use the * same encryption policy. The pre-access check is needed to detect potentially * malicious offline violations of this constraint, while the link and rename * checks are needed to prevent online violations of this constraint. * * Return: 1 if permitted, 0 if forbidden. If forbidden, the caller must fail * the filesystem operation with EPERM. */ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child) { const struct fscrypt_operations *cops = parent->i_sb->s_cop; const struct fscrypt_info *parent_ci, *child_ci; struct fscrypt_context parent_ctx, child_ctx; int res; /* No restrictions on file types which are never encrypted */ if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) && !S_ISLNK(child->i_mode)) return 1; /* No restrictions if the parent directory is unencrypted */ if (!IS_ENCRYPTED(parent)) return 1; /* Encrypted directories must not contain unencrypted files */ if (!IS_ENCRYPTED(child)) return 0; /* * Both parent and child are encrypted, so verify they use the same * encryption policy. Compare the fscrypt_info structs if the keys are * available, otherwise retrieve and compare the fscrypt_contexts. * * Note that the fscrypt_context retrieval will be required frequently * when accessing an encrypted directory tree without the key. * Performance-wise this is not a big deal because we already don't * really optimize for file access without the key (to the extent that * such access is even possible), given that any attempted access * already causes a fscrypt_context retrieval and keyring search. * * In any case, if an unexpected error occurs, fall back to "forbidden". */ res = fscrypt_get_encryption_info(parent); if (res) return 0; res = fscrypt_get_encryption_info(child); if (res) return 0; parent_ci = parent->i_crypt_info; child_ci = child->i_crypt_info; if (parent_ci && child_ci) { return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key, FS_KEY_DESCRIPTOR_SIZE) == 0 && (parent_ci->ci_data_mode == child_ci->ci_data_mode) && (parent_ci->ci_filename_mode == child_ci->ci_filename_mode) && (parent_ci->ci_flags == child_ci->ci_flags); } res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx)); if (res != sizeof(parent_ctx)) return 0; res = cops->get_context(child, &child_ctx, sizeof(child_ctx)); if (res != sizeof(child_ctx)) return 0; return memcmp(parent_ctx.master_key_descriptor, child_ctx.master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE) == 0 && (parent_ctx.contents_encryption_mode == child_ctx.contents_encryption_mode) && (parent_ctx.filenames_encryption_mode == child_ctx.filenames_encryption_mode) && (parent_ctx.flags == child_ctx.flags); } EXPORT_SYMBOL(fscrypt_has_permitted_context); /** * fscrypt_inherit_context() - Sets a child context from its parent * @parent: Parent inode from which the context is inherited. * @child: Child inode that inherits the context from @parent. * @fs_data: private data given by FS. * @preload: preload child i_crypt_info if true * * Return: 0 on success, -errno on failure */ int fscrypt_inherit_context(struct inode *parent, struct inode *child, void *fs_data, bool preload) { struct fscrypt_context ctx; struct fscrypt_info *ci; int res; res = fscrypt_get_encryption_info(parent); if (res < 0) return res; ci = parent->i_crypt_info; if (ci == NULL) return -ENOKEY; ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1; ctx.contents_encryption_mode = ci->ci_data_mode; ctx.filenames_encryption_mode = ci->ci_filename_mode; ctx.flags = ci->ci_flags; memcpy(ctx.master_key_descriptor, ci->ci_master_key, FS_KEY_DESCRIPTOR_SIZE); get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE); BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE); res = parent->i_sb->s_cop->set_context(child, &ctx, sizeof(ctx), fs_data); if (res) return res; return preload ? fscrypt_get_encryption_info(child): 0; } EXPORT_SYMBOL(fscrypt_inherit_context);