// SPDX-License-Identifier: GPL-2.0 /* * Encryption policy functions for per-file encryption support. * * Copyright (C) 2015, Google, Inc. * Copyright (C) 2015, Motorola Mobility. * * Originally written by Michael Halcrow, 2015. * Modified by Jaegeuk Kim, 2015. * Modified by Eric Biggers, 2019 for v2 policy support. */ #include #include #include #include "fscrypt_private.h" /** * fscrypt_policies_equal - check whether two encryption policies are the same * * Return: %true if equal, else %false */ bool fscrypt_policies_equal(const union fscrypt_policy *policy1, const union fscrypt_policy *policy2) { if (policy1->version != policy2->version) return false; return !memcmp(policy1, policy2, fscrypt_policy_size(policy1)); } static bool fscrypt_valid_enc_modes(u32 contents_mode, u32 filenames_mode) { if (contents_mode == FSCRYPT_MODE_AES_256_XTS && filenames_mode == FSCRYPT_MODE_AES_256_CTS) return true; if (contents_mode == FSCRYPT_MODE_AES_128_CBC && filenames_mode == FSCRYPT_MODE_AES_128_CTS) return true; if (contents_mode == FSCRYPT_MODE_ADIANTUM && filenames_mode == FSCRYPT_MODE_ADIANTUM) return true; return false; } static bool supported_direct_key_modes(const struct inode *inode, u32 contents_mode, u32 filenames_mode) { const struct fscrypt_mode *mode; if (contents_mode != filenames_mode) { fscrypt_warn(inode, "Direct key flag not allowed with different contents and filenames modes"); return false; } mode = &fscrypt_modes[contents_mode]; if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) { fscrypt_warn(inode, "Direct key flag not allowed with %s", mode->friendly_name); return false; } return true; } static bool supported_iv_ino_lblk_64_policy( const struct fscrypt_policy_v2 *policy, const struct inode *inode) { struct super_block *sb = inode->i_sb; int ino_bits = 64, lblk_bits = 64; if (policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) { fscrypt_warn(inode, "The DIRECT_KEY and IV_INO_LBLK_64 flags are mutually exclusive"); return false; } /* * It's unsafe to include inode numbers in the IVs if the filesystem can * potentially renumber inodes, e.g. via filesystem shrinking. */ if (!sb->s_cop->has_stable_inodes || !sb->s_cop->has_stable_inodes(sb)) { fscrypt_warn(inode, "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't have stable inode numbers", sb->s_id); return false; } if (sb->s_cop->get_ino_and_lblk_bits) sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits); if (ino_bits > 32 || lblk_bits > 32) { fscrypt_warn(inode, "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't use 32-bit inode and block numbers", sb->s_id); return false; } return true; } static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy, const struct inode *inode) { if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode, policy->filenames_encryption_mode)) { fscrypt_warn(inode, "Unsupported encryption modes (contents %d, filenames %d)", policy->contents_encryption_mode, policy->filenames_encryption_mode); return false; } if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK | FSCRYPT_POLICY_FLAG_DIRECT_KEY)) { fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)", policy->flags); return false; } if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) && !supported_direct_key_modes(inode, policy->contents_encryption_mode, policy->filenames_encryption_mode)) return false; return true; } static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy, const struct inode *inode) { if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode, policy->filenames_encryption_mode)) { fscrypt_warn(inode, "Unsupported encryption modes (contents %d, filenames %d)", policy->contents_encryption_mode, policy->filenames_encryption_mode); return false; } if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID) { fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)", policy->flags); return false; } if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) && !supported_direct_key_modes(inode, policy->contents_encryption_mode, policy->filenames_encryption_mode)) return false; if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) && !supported_iv_ino_lblk_64_policy(policy, inode)) return false; if (memchr_inv(policy->__reserved, 0, sizeof(policy->__reserved))) { fscrypt_warn(inode, "Reserved bits set in encryption policy"); return false; } return true; } /** * fscrypt_supported_policy - check whether an encryption policy is supported * * Given an encryption policy, check whether all its encryption modes and other * settings are supported by this kernel on the given inode. (But we don't * currently don't check for crypto API support here, so attempting to use an * algorithm not configured into the crypto API will still fail later.) * * Return: %true if supported, else %false */ bool fscrypt_supported_policy(const union fscrypt_policy *policy_u, const struct inode *inode) { switch (policy_u->version) { case FSCRYPT_POLICY_V1: return fscrypt_supported_v1_policy(&policy_u->v1, inode); case FSCRYPT_POLICY_V2: return fscrypt_supported_v2_policy(&policy_u->v2, inode); } return false; } /** * fscrypt_new_context_from_policy - create a new fscrypt_context from a policy * * Create an fscrypt_context for an inode that is being assigned the given * encryption policy. A new nonce is randomly generated. * * Return: the size of the new context in bytes. */ static int fscrypt_new_context_from_policy(union fscrypt_context *ctx_u, const union fscrypt_policy *policy_u) { memset(ctx_u, 0, sizeof(*ctx_u)); switch (policy_u->version) { case FSCRYPT_POLICY_V1: { const struct fscrypt_policy_v1 *policy = &policy_u->v1; struct fscrypt_context_v1 *ctx = &ctx_u->v1; ctx->version = FSCRYPT_CONTEXT_V1; ctx->contents_encryption_mode = policy->contents_encryption_mode; ctx->filenames_encryption_mode = policy->filenames_encryption_mode; ctx->flags = policy->flags; memcpy(ctx->master_key_descriptor, policy->master_key_descriptor, sizeof(ctx->master_key_descriptor)); get_random_bytes(ctx->nonce, sizeof(ctx->nonce)); return sizeof(*ctx); } case FSCRYPT_POLICY_V2: { const struct fscrypt_policy_v2 *policy = &policy_u->v2; struct fscrypt_context_v2 *ctx = &ctx_u->v2; ctx->version = FSCRYPT_CONTEXT_V2; ctx->contents_encryption_mode = policy->contents_encryption_mode; ctx->filenames_encryption_mode = policy->filenames_encryption_mode; ctx->flags = policy->flags; memcpy(ctx->master_key_identifier, policy->master_key_identifier, sizeof(ctx->master_key_identifier)); get_random_bytes(ctx->nonce, sizeof(ctx->nonce)); return sizeof(*ctx); } } BUG(); } /** * fscrypt_policy_from_context - convert an fscrypt_context to an fscrypt_policy * * Given an fscrypt_context, build the corresponding fscrypt_policy. * * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized * version number or size. * * This does *not* validate the settings within the policy itself, e.g. the * modes, flags, and reserved bits. Use fscrypt_supported_policy() for that. */ int fscrypt_policy_from_context(union fscrypt_policy *policy_u, const union fscrypt_context *ctx_u, int ctx_size) { memset(policy_u, 0, sizeof(*policy_u)); if (ctx_size <= 0 || ctx_size != fscrypt_context_size(ctx_u)) return -EINVAL; switch (ctx_u->version) { case FSCRYPT_CONTEXT_V1: { const struct fscrypt_context_v1 *ctx = &ctx_u->v1; struct fscrypt_policy_v1 *policy = &policy_u->v1; policy->version = FSCRYPT_POLICY_V1; 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, sizeof(policy->master_key_descriptor)); return 0; } case FSCRYPT_CONTEXT_V2: { const struct fscrypt_context_v2 *ctx = &ctx_u->v2; struct fscrypt_policy_v2 *policy = &policy_u->v2; policy->version = FSCRYPT_POLICY_V2; policy->contents_encryption_mode = ctx->contents_encryption_mode; policy->filenames_encryption_mode = ctx->filenames_encryption_mode; policy->flags = ctx->flags; memcpy(policy->__reserved, ctx->__reserved, sizeof(policy->__reserved)); memcpy(policy->master_key_identifier, ctx->master_key_identifier, sizeof(policy->master_key_identifier)); return 0; } } /* unreachable */ return -EINVAL; } /* Retrieve an inode's encryption policy */ static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy) { const struct fscrypt_info *ci; union fscrypt_context ctx; int ret; ci = READ_ONCE(inode->i_crypt_info); if (ci) { /* key available, use the cached policy */ *policy = ci->ci_policy; return 0; } if (!IS_ENCRYPTED(inode)) return -ENODATA; ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx)); if (ret < 0) return (ret == -ERANGE) ? -EINVAL : ret; return fscrypt_policy_from_context(policy, &ctx, ret); } static int set_encryption_policy(struct inode *inode, const union fscrypt_policy *policy) { union fscrypt_context ctx; int ctxsize; int err; if (!fscrypt_supported_policy(policy, inode)) return -EINVAL; switch (policy->version) { case FSCRYPT_POLICY_V1: /* * The original encryption policy version provided no way of * verifying that the correct master key was supplied, which was * insecure in scenarios where multiple users have access to the * same encrypted files (even just read-only access). The new * encryption policy version fixes this and also implies use of * an improved key derivation function and allows non-root users * to securely remove keys. So as long as compatibility with * old kernels isn't required, it is recommended to use the new * policy version for all new encrypted directories. */ pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n", current->comm, current->pid); break; case FSCRYPT_POLICY_V2: err = fscrypt_verify_key_added(inode->i_sb, policy->v2.master_key_identifier); if (err) return err; break; default: WARN_ON(1); return -EINVAL; } ctxsize = fscrypt_new_context_from_policy(&ctx, policy); return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL); } int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg) { union fscrypt_policy policy; union fscrypt_policy existing_policy; struct inode *inode = file_inode(filp); u8 version; int size; int ret; if (get_user(policy.version, (const u8 __user *)arg)) return -EFAULT; size = fscrypt_policy_size(&policy); if (size <= 0) return -EINVAL; /* * We should just copy the remaining 'size - 1' bytes here, but a * bizarre bug in gcc 7 and earlier (fixed by gcc r255731) causes gcc to * think that size can be 0 here (despite the check above!) *and* that * it's a compile-time constant. Thus it would think copy_from_user() * is passed compile-time constant ULONG_MAX, causing the compile-time * buffer overflow check to fail, breaking the build. This only occurred * when building an i386 kernel with -Os and branch profiling enabled. * * Work around it by just copying the first byte again... */ version = policy.version; if (copy_from_user(&policy, arg, size)) return -EFAULT; policy.version = version; if (!inode_owner_or_capable(inode)) return -EACCES; ret = mnt_want_write_file(filp); if (ret) return ret; inode_lock(inode); ret = fscrypt_get_policy(inode, &existing_policy); if (ret == -ENODATA) { if (!S_ISDIR(inode->i_mode)) ret = -ENOTDIR; else if (IS_DEADDIR(inode)) ret = -ENOENT; else if (!inode->i_sb->s_cop->empty_dir(inode)) ret = -ENOTEMPTY; else ret = set_encryption_policy(inode, &policy); } else if (ret == -EINVAL || (ret == 0 && !fscrypt_policies_equal(&policy, &existing_policy))) { /* 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); /* Original ioctl version; can only get the original policy version */ int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg) { union fscrypt_policy policy; int err; err = fscrypt_get_policy(file_inode(filp), &policy); if (err) return err; if (policy.version != FSCRYPT_POLICY_V1) return -EINVAL; if (copy_to_user(arg, &policy, sizeof(policy.v1))) return -EFAULT; return 0; } EXPORT_SYMBOL(fscrypt_ioctl_get_policy); /* Extended ioctl version; can get policies of any version */ int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg) { struct fscrypt_get_policy_ex_arg arg; union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy; size_t policy_size; int err; /* arg is policy_size, then policy */ BUILD_BUG_ON(offsetof(typeof(arg), policy_size) != 0); BUILD_BUG_ON(offsetofend(typeof(arg), policy_size) != offsetof(typeof(arg), policy)); BUILD_BUG_ON(sizeof(arg.policy) != sizeof(*policy)); err = fscrypt_get_policy(file_inode(filp), policy); if (err) return err; policy_size = fscrypt_policy_size(policy); if (copy_from_user(&arg, uarg, sizeof(arg.policy_size))) return -EFAULT; if (policy_size > arg.policy_size) return -EOVERFLOW; arg.policy_size = policy_size; if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size)) return -EFAULT; return 0; } EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex); /** * 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. */ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child) { union fscrypt_policy parent_policy, child_policy; int err; /* 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". */ err = fscrypt_get_encryption_info(parent); if (err) return 0; err = fscrypt_get_encryption_info(child); if (err) return 0; err = fscrypt_get_policy(parent, &parent_policy); if (err) return 0; err = fscrypt_get_policy(child, &child_policy); if (err) return 0; return fscrypt_policies_equal(&parent_policy, &child_policy); } 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) { union fscrypt_context ctx; int ctxsize; struct fscrypt_info *ci; int res; res = fscrypt_get_encryption_info(parent); if (res < 0) return res; ci = READ_ONCE(parent->i_crypt_info); if (ci == NULL) return -ENOKEY; ctxsize = fscrypt_new_context_from_policy(&ctx, &ci->ci_policy); BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE); res = parent->i_sb->s_cop->set_context(child, &ctx, ctxsize, fs_data); if (res) return res; return preload ? fscrypt_get_encryption_info(child): 0; } EXPORT_SYMBOL(fscrypt_inherit_context);