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