// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * eCryptfs: Linux filesystem encryption layer
 * This is where eCryptfs coordinates the symmetric encryption and
 * decryption of the file data as it passes between the lower
 * encrypted file and the upper decrypted file.
 *
 * Copyright (C) 1997-2003 Erez Zadok
 * Copyright (C) 2001-2003 Stony Brook University
 * Copyright (C) 2004-2007 International Business Machines Corp.
 *   Author(s): Michael A. Halcrow <mahalcro@us.ibm.com>
 */

#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/page-flags.h>
#include <linux/mount.h>
#include <linux/file.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>
#include <linux/xattr.h>
#include <linux/unaligned.h>
#include "ecryptfs_kernel.h"

/*
 * This is where we encrypt the data and pass the encrypted data to
 * the lower filesystem.  In OpenPGP-compatible mode, we operate on
 * entire underlying packets.
 */
static int ecryptfs_writepages(struct address_space *mapping,
                struct writeback_control *wbc)
{
        struct folio *folio = NULL;
        int error;

        while ((folio = writeback_iter(mapping, wbc, folio, &error))) {
                error = ecryptfs_encrypt_page(folio);
                if (error) {
                        ecryptfs_printk(KERN_WARNING,
                                "Error encrypting folio (index [0x%.16lx])\n",
                                folio->index);
                        folio_clear_uptodate(folio);
                        mapping_set_error(mapping, error);
                }
                folio_unlock(folio);
        }

        return error;
}

static void strip_xattr_flag(char *page_virt,
                             struct ecryptfs_crypt_stat *crypt_stat)
{
        if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
                size_t written;

                crypt_stat->flags &= ~ECRYPTFS_METADATA_IN_XATTR;
                ecryptfs_write_crypt_stat_flags(page_virt, crypt_stat,
                                                &written);
                crypt_stat->flags |= ECRYPTFS_METADATA_IN_XATTR;
        }
}

/*
 *   Header Extent:
 *     Octets 0-7:        Unencrypted file size (big-endian)
 *     Octets 8-15:       eCryptfs special marker
 *     Octets 16-19:      Flags
 *      Octet 16:         File format version number (between 0 and 255)
 *      Octets 17-18:     Reserved
 *      Octet 19:         Bit 1 (lsb): Reserved
 *                        Bit 2: Encrypted?
 *                        Bits 3-8: Reserved
 *     Octets 20-23:      Header extent size (big-endian)
 *     Octets 24-25:      Number of header extents at front of file
 *                        (big-endian)
 *     Octet  26:         Begin RFC 2440 authentication token packet set
 */

/**
 * ecryptfs_copy_up_encrypted_with_header
 * @folio: Sort of a ``virtual'' representation of the encrypted lower
 *        file. The actual lower file does not have the metadata in
 *        the header. This is locked.
 * @crypt_stat: The eCryptfs inode's cryptographic context
 *
 * The ``view'' is the version of the file that userspace winds up
 * seeing, with the header information inserted.
 */
static int
ecryptfs_copy_up_encrypted_with_header(struct folio *folio,
                                       struct ecryptfs_crypt_stat *crypt_stat)
{
        loff_t extent_num_in_page = 0;
        loff_t num_extents_per_page = (PAGE_SIZE
                                       / crypt_stat->extent_size);
        int rc = 0;

        while (extent_num_in_page < num_extents_per_page) {
                loff_t view_extent_num = ((loff_t)folio->index
                                           * num_extents_per_page)
                                          + extent_num_in_page;
                size_t num_header_extents_at_front =
                        (crypt_stat->metadata_size / crypt_stat->extent_size);

                if (view_extent_num < num_header_extents_at_front) {
                        /* This is a header extent */
                        char *page_virt;

                        page_virt = kmap_local_folio(folio, 0);
                        memset(page_virt, 0, PAGE_SIZE);
                        /* TODO: Support more than one header extent */
                        if (view_extent_num == 0) {
                                size_t written;

                                rc = ecryptfs_read_xattr_region(
                                        page_virt, folio->mapping->host);
                                strip_xattr_flag(page_virt + 16, crypt_stat);
                                ecryptfs_write_header_metadata(page_virt + 20,
                                                               crypt_stat,
                                                               &written);
                        }
                        kunmap_local(page_virt);
                        flush_dcache_folio(folio);
                        if (rc) {
                                printk(KERN_ERR "%s: Error reading xattr "
                                       "region; rc = [%d]\n", __func__, rc);
                                goto out;
                        }
                } else {
                        /* This is an encrypted data extent */
                        loff_t lower_offset =
                                ((view_extent_num * crypt_stat->extent_size)
                                 - crypt_stat->metadata_size);

                        rc = ecryptfs_read_lower_page_segment(
                                folio, (lower_offset >> PAGE_SHIFT),
                                (lower_offset & ~PAGE_MASK),
                                crypt_stat->extent_size, folio->mapping->host);
                        if (rc) {
                                printk(KERN_ERR "%s: Error attempting to read "
                                       "extent at offset [%lld] in the lower "
                                       "file; rc = [%d]\n", __func__,
                                       lower_offset, rc);
                                goto out;
                        }
                }
                extent_num_in_page++;
        }
out:
        return rc;
}

/**
 * ecryptfs_read_folio
 * @file: An eCryptfs file
 * @folio: Folio from eCryptfs inode mapping into which to stick the read data
 *
 * Read in a folio, decrypting if necessary.
 *
 * Returns zero on success; non-zero on error.
 */
static int ecryptfs_read_folio(struct file *file, struct folio *folio)
{
        struct inode *inode = folio->mapping->host;
        struct ecryptfs_crypt_stat *crypt_stat =
                &ecryptfs_inode_to_private(inode)->crypt_stat;
        int err = 0;

        if (!crypt_stat || !(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
                err = ecryptfs_read_lower_page_segment(folio, folio->index, 0,
                                folio_size(folio), inode);
        } else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
                if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
                        err = ecryptfs_copy_up_encrypted_with_header(folio,
                                        crypt_stat);
                        if (err) {
                                printk(KERN_ERR "%s: Error attempting to copy "
                                       "the encrypted content from the lower "
                                       "file whilst inserting the metadata "
                                       "from the xattr into the header; err = "
                                       "[%d]\n", __func__, err);
                                goto out;
                        }

                } else {
                        err = ecryptfs_read_lower_page_segment(folio,
                                        folio->index, 0, folio_size(folio),
                                        inode);
                        if (err) {
                                printk(KERN_ERR "Error reading page; err = "
                                       "[%d]\n", err);
                                goto out;
                        }
                }
        } else {
                err = ecryptfs_decrypt_page(folio);
                if (err) {
                        ecryptfs_printk(KERN_ERR, "Error decrypting page; "
                                        "err = [%d]\n", err);
                        goto out;
                }
        }
out:
        ecryptfs_printk(KERN_DEBUG, "Unlocking folio with index = [0x%.16lx]\n",
                        folio->index);
        folio_end_read(folio, err == 0);
        return err;
}

/*
 * Called with lower inode mutex held.
 */
static int fill_zeros_to_end_of_page(struct folio *folio, unsigned int to)
{
        struct inode *inode = folio->mapping->host;
        int end_byte_in_page;

        if ((i_size_read(inode) / PAGE_SIZE) != folio->index)
                goto out;
        end_byte_in_page = i_size_read(inode) % PAGE_SIZE;
        if (to > end_byte_in_page)
                end_byte_in_page = to;
        folio_zero_segment(folio, end_byte_in_page, PAGE_SIZE);
out:
        return 0;
}

/**
 * ecryptfs_write_begin
 * @iocb: I/O control block for the eCryptfs file
 * @mapping: The eCryptfs object
 * @pos: The file offset at which to start writing
 * @len: Length of the write
 * @foliop: Pointer to return the folio
 * @fsdata: Pointer to return fs data (unused)
 *
 * This function must zero any hole we create
 *
 * Returns zero on success; non-zero otherwise
 */
static int ecryptfs_write_begin(const struct kiocb *iocb,
                        struct address_space *mapping,
                        loff_t pos, unsigned len,
                        struct folio **foliop, void **fsdata)
{
        pgoff_t index = pos >> PAGE_SHIFT;
        struct folio *folio;
        loff_t prev_page_end_size;
        int rc = 0;

        folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
                        mapping_gfp_mask(mapping));
        if (IS_ERR(folio))
                return PTR_ERR(folio);
        *foliop = folio;

        prev_page_end_size = ((loff_t)index << PAGE_SHIFT);
        if (!folio_test_uptodate(folio)) {
                struct ecryptfs_crypt_stat *crypt_stat =
                        &ecryptfs_inode_to_private(mapping->host)->crypt_stat;

                if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
                        rc = ecryptfs_read_lower_page_segment(
                                folio, index, 0, PAGE_SIZE, mapping->host);
                        if (rc) {
                                printk(KERN_ERR "%s: Error attempting to read "
                                       "lower page segment; rc = [%d]\n",
                                       __func__, rc);
                                folio_clear_uptodate(folio);
                                goto out;
                        } else
                                folio_mark_uptodate(folio);
                } else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
                        if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
                                rc = ecryptfs_copy_up_encrypted_with_header(
                                        folio, crypt_stat);
                                if (rc) {
                                        printk(KERN_ERR "%s: Error attempting "
                                               "to copy the encrypted content "
                                               "from the lower file whilst "
                                               "inserting the metadata from "
                                               "the xattr into the header; rc "
                                               "= [%d]\n", __func__, rc);
                                        folio_clear_uptodate(folio);
                                        goto out;
                                }
                                folio_mark_uptodate(folio);
                        } else {
                                rc = ecryptfs_read_lower_page_segment(
                                        folio, index, 0, PAGE_SIZE,
                                        mapping->host);
                                if (rc) {
                                        printk(KERN_ERR "%s: Error reading "
                                               "page; rc = [%d]\n",
                                               __func__, rc);
                                        folio_clear_uptodate(folio);
                                        goto out;
                                }
                                folio_mark_uptodate(folio);
                        }
                } else {
                        if (prev_page_end_size
                            >= i_size_read(mapping->host)) {
                                folio_zero_range(folio, 0, PAGE_SIZE);
                                folio_mark_uptodate(folio);
                        } else if (len < PAGE_SIZE) {
                                rc = ecryptfs_decrypt_page(folio);
                                if (rc) {
                                        printk(KERN_ERR "%s: Error decrypting "
                                               "page at index [%ld]; "
                                               "rc = [%d]\n",
                                               __func__, folio->index, rc);
                                        folio_clear_uptodate(folio);
                                        goto out;
                                }
                                folio_mark_uptodate(folio);
                        }
                }
        }
        /* If creating a page or more of holes, zero them out via truncate.
         * Note, this will increase i_size. */
        if (index != 0) {
                if (prev_page_end_size > i_size_read(mapping->host)) {
                        rc = ecryptfs_truncate(iocb->ki_filp->f_path.dentry,
                                               prev_page_end_size);
                        if (rc) {
                                printk(KERN_ERR "%s: Error on attempt to "
                                       "truncate to (higher) offset [%lld];"
                                       " rc = [%d]\n", __func__,
                                       prev_page_end_size, rc);
                                goto out;
                        }
                }
        }
        /* Writing to a new page, and creating a small hole from start
         * of page?  Zero it out. */
        if ((i_size_read(mapping->host) == prev_page_end_size)
            && (pos != 0))
                folio_zero_range(folio, 0, PAGE_SIZE);
out:
        if (unlikely(rc)) {
                folio_unlock(folio);
                folio_put(folio);
        }
        return rc;
}

/*
 * ecryptfs_write_inode_size_to_header
 *
 * Writes the lower file size to the first 8 bytes of the header.
 *
 * Returns zero on success; non-zero on error.
 */
static int ecryptfs_write_inode_size_to_header(struct inode *ecryptfs_inode)
{
        char *file_size_virt;
        int rc;

        file_size_virt = kmalloc(sizeof(u64), GFP_KERNEL);
        if (!file_size_virt) {
                rc = -ENOMEM;
                goto out;
        }
        put_unaligned_be64(i_size_read(ecryptfs_inode), file_size_virt);
        rc = ecryptfs_write_lower(ecryptfs_inode, file_size_virt, 0,
                                  sizeof(u64));
        kfree(file_size_virt);
        if (rc < 0)
                printk(KERN_ERR "%s: Error writing file size to header; "
                       "rc = [%d]\n", __func__, rc);
        else
                rc = 0;
out:
        return rc;
}

struct kmem_cache *ecryptfs_xattr_cache;

static int ecryptfs_write_inode_size_to_xattr(struct inode *ecryptfs_inode)
{
        ssize_t size;
        void *xattr_virt;
        struct dentry *lower_dentry =
                ecryptfs_inode_to_private(ecryptfs_inode)->lower_file->f_path.dentry;
        struct inode *lower_inode = d_inode(lower_dentry);
        int rc;

        if (!(lower_inode->i_opflags & IOP_XATTR)) {
                printk(KERN_WARNING
                       "No support for setting xattr in lower filesystem\n");
                rc = -ENOSYS;
                goto out;
        }
        xattr_virt = kmem_cache_alloc(ecryptfs_xattr_cache, GFP_KERNEL);
        if (!xattr_virt) {
                rc = -ENOMEM;
                goto out;
        }
        inode_lock(lower_inode);
        size = __vfs_getxattr(lower_dentry, lower_inode, ECRYPTFS_XATTR_NAME,
                              xattr_virt, PAGE_SIZE);
        if (size < 0)
                size = 8;
        put_unaligned_be64(i_size_read(ecryptfs_inode), xattr_virt);
        rc = __vfs_setxattr(&nop_mnt_idmap, lower_dentry, lower_inode,
                            ECRYPTFS_XATTR_NAME, xattr_virt, size, 0);
        inode_unlock(lower_inode);
        if (rc)
                printk(KERN_ERR "Error whilst attempting to write inode size "
                       "to lower file xattr; rc = [%d]\n", rc);
        kmem_cache_free(ecryptfs_xattr_cache, xattr_virt);
out:
        return rc;
}

int ecryptfs_write_inode_size_to_metadata(struct inode *ecryptfs_inode)
{
        struct ecryptfs_crypt_stat *crypt_stat;

        crypt_stat = &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;
        BUG_ON(!(crypt_stat->flags & ECRYPTFS_ENCRYPTED));
        if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR)
                return ecryptfs_write_inode_size_to_xattr(ecryptfs_inode);
        else
                return ecryptfs_write_inode_size_to_header(ecryptfs_inode);
}

/**
 * ecryptfs_write_end
 * @iocb: I/O control block for the eCryptfs file
 * @mapping: The eCryptfs object
 * @pos: The file position
 * @len: The length of the data (unused)
 * @copied: The amount of data copied
 * @folio: The eCryptfs folio
 * @fsdata: The fsdata (unused)
 */
static int ecryptfs_write_end(const struct kiocb *iocb,
                        struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct folio *folio, void *fsdata)
{
        pgoff_t index = pos >> PAGE_SHIFT;
        unsigned from = pos & (PAGE_SIZE - 1);
        unsigned to = from + copied;
        struct inode *ecryptfs_inode = mapping->host;
        struct ecryptfs_crypt_stat *crypt_stat =
                &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;
        int rc;

        ecryptfs_printk(KERN_DEBUG, "Calling fill_zeros_to_end_of_page"
                        "(page w/ index = [0x%.16lx], to = [%d])\n", index, to);
        if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
                rc = ecryptfs_write_lower_page_segment(ecryptfs_inode,
                                folio, 0, to);
                if (!rc) {
                        rc = copied;
                        fsstack_copy_inode_size(ecryptfs_inode,
                                ecryptfs_inode_to_lower(ecryptfs_inode));
                }
                goto out;
        }
        if (!folio_test_uptodate(folio)) {
                if (copied < PAGE_SIZE) {
                        rc = 0;
                        goto out;
                }
                folio_mark_uptodate(folio);
        }
        /* Fills in zeros if 'to' goes beyond inode size */
        rc = fill_zeros_to_end_of_page(folio, to);
        if (rc) {
                ecryptfs_printk(KERN_WARNING, "Error attempting to fill "
                        "zeros in page with index = [0x%.16lx]\n", index);
                goto out;
        }
        rc = ecryptfs_encrypt_page(folio);
        if (rc) {
                ecryptfs_printk(KERN_WARNING, "Error encrypting page (upper "
                                "index [0x%.16lx])\n", index);
                goto out;
        }
        if (pos + copied > i_size_read(ecryptfs_inode)) {
                i_size_write(ecryptfs_inode, pos + copied);
                ecryptfs_printk(KERN_DEBUG, "Expanded file size to "
                        "[0x%.16llx]\n",
                        (unsigned long long)i_size_read(ecryptfs_inode));
        }
        rc = ecryptfs_write_inode_size_to_metadata(ecryptfs_inode);
        if (rc)
                printk(KERN_ERR "Error writing inode size to metadata; "
                       "rc = [%d]\n", rc);
        else
                rc = copied;
out:
        folio_unlock(folio);
        folio_put(folio);
        return rc;
}

static sector_t ecryptfs_bmap(struct address_space *mapping, sector_t block)
{
        struct inode *lower_inode = ecryptfs_inode_to_lower(mapping->host);
        int ret = bmap(lower_inode, &block);

        if (ret)
                return 0;
        return block;
}

#include <linux/buffer_head.h>

const struct address_space_operations ecryptfs_aops = {
        /*
         * XXX: This is pretty broken for multiple reasons: ecryptfs does not
         * actually use buffer_heads, and ecryptfs will crash without
         * CONFIG_BLOCK.  But it matches the behavior before the default for
         * address_space_operations without the ->dirty_folio method was
         * cleaned up, so this is the best we can do without maintainer
         * feedback.
         */
#ifdef CONFIG_BLOCK
        .dirty_folio    = block_dirty_folio,
        .invalidate_folio = block_invalidate_folio,
#endif
        .writepages = ecryptfs_writepages,
        .read_folio = ecryptfs_read_folio,
        .write_begin = ecryptfs_write_begin,
        .write_end = ecryptfs_write_end,
        .migrate_folio = filemap_migrate_folio,
        .bmap = ecryptfs_bmap,
};