diff options
Diffstat (limited to 'fs/crypto/policy.c')
| -rw-r--r-- | fs/crypto/policy.c | 269 |
1 files changed, 269 insertions, 0 deletions
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c new file mode 100644 index 000000000000..210976e7a269 --- /dev/null +++ b/fs/crypto/policy.c @@ -0,0 +1,269 @@ +/* + * 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_contents_enc_mode( + policy->contents_encryption_mode)) + return -EINVAL; + + if (!fscrypt_valid_filenames_enc_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 (!inode->i_sb->s_cop->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 (!cops->is_encrypted(parent)) + return 1; + + /* Encrypted directories must not contain unencrypted files */ + if (!cops->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); + 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); |