// SPDX-License-Identifier: GPL-2.0
/*
 * fs/f2fs/verity.c: fs-verity support for f2fs
 *
 * Copyright 2019 Google LLC
 */

/*
 * Implementation of fsverity_operations for f2fs.
 *
 * Like ext4, f2fs stores the verity metadata (Merkle tree and
 * fsverity_descriptor) past the end of the file, starting at the first 64K
 * boundary beyond i_size.  This approach works because (a) verity files are
 * readonly, and (b) pages fully beyond i_size aren't visible to userspace but
 * can be read/written internally by f2fs with only some relatively small
 * changes to f2fs.  Extended attributes cannot be used because (a) f2fs limits
 * the total size of an inode's xattr entries to 4096 bytes, which wouldn't be
 * enough for even a single Merkle tree block, and (b) f2fs encryption doesn't
 * encrypt xattrs, yet the verity metadata *must* be encrypted when the file is
 * because it contains hashes of the plaintext data.
 *
 * Using a 64K boundary rather than a 4K one keeps things ready for
 * architectures with 64K pages, and it doesn't necessarily waste space on-disk
 * since there can be a hole between i_size and the start of the Merkle tree.
 */

#include <linux/f2fs_fs.h>

#include "f2fs.h"
#include "xattr.h"

#define F2FS_VERIFY_VER (1)

static inline loff_t f2fs_verity_metadata_pos(const struct inode *inode)
{
        return round_up(inode->i_size, 65536);
}

/*
 * Read some verity metadata from the inode.  __vfs_read() can't be used because
 * we need to read beyond i_size.
 */
static int pagecache_read(struct inode *inode, void *buf, size_t count,
                          loff_t pos)
{
        while (count) {
                size_t n = min_t(size_t, count,
                                 PAGE_SIZE - offset_in_page(pos));
                struct page *page;

                page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
                                         NULL);
                if (IS_ERR(page))
                        return PTR_ERR(page);

                memcpy_from_page(buf, page, offset_in_page(pos), n);

                put_page(page);

                buf += n;
                pos += n;
                count -= n;
        }
        return 0;
}

/*
 * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
 * kernel_write() can't be used because the file descriptor is readonly.
 */
static int pagecache_write(struct inode *inode, const void *buf, size_t count,
                           loff_t pos)
{
        struct address_space *mapping = inode->i_mapping;
        const struct address_space_operations *aops = mapping->a_ops;

        if (pos + count > F2FS_BLK_TO_BYTES(max_file_blocks(inode)))
                return -EFBIG;

        while (count) {
                size_t n = min_t(size_t, count,
                                 PAGE_SIZE - offset_in_page(pos));
                struct folio *folio;
                void *fsdata = NULL;
                int res;

                res = aops->write_begin(NULL, mapping, pos, n, &folio, &fsdata);
                if (res)
                        return res;

                memcpy_to_folio(folio, offset_in_folio(folio, pos), buf, n);

                res = aops->write_end(NULL, mapping, pos, n, n, folio, fsdata);
                if (res < 0)
                        return res;
                if (res != n)
                        return -EIO;

                buf += n;
                pos += n;
                count -= n;
        }
        return 0;
}

/*
 * Format of f2fs verity xattr.  This points to the location of the verity
 * descriptor within the file data rather than containing it directly because
 * the verity descriptor *must* be encrypted when f2fs encryption is used.  But,
 * f2fs encryption does not encrypt xattrs.
 */
struct fsverity_descriptor_location {
        __le32 version;
        __le32 size;
        __le64 pos;
};

static int f2fs_begin_enable_verity(struct file *filp)
{
        struct inode *inode = file_inode(filp);
        int err;

        if (f2fs_verity_in_progress(inode))
                return -EBUSY;

        if (f2fs_is_atomic_file(inode))
                return -EOPNOTSUPP;

        /*
         * Since the file was opened readonly, we have to initialize the quotas
         * here and not rely on ->open() doing it.  This must be done before
         * evicting the inline data.
         */
        err = f2fs_dquot_initialize(inode);
        if (err)
                return err;

        err = f2fs_convert_inline_inode(inode);
        if (err)
                return err;

        set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
        return 0;
}

static int f2fs_end_enable_verity(struct file *filp, const void *desc,
                                  size_t desc_size, u64 merkle_tree_size)
{
        struct inode *inode = file_inode(filp);
        struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
        u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
        struct fsverity_descriptor_location dloc = {
                .version = cpu_to_le32(F2FS_VERIFY_VER),
                .size = cpu_to_le32(desc_size),
                .pos = cpu_to_le64(desc_pos),
        };
        int err = 0, err2 = 0;

        /*
         * If an error already occurred (which fs/verity/ signals by passing
         * desc == NULL), then only clean-up is needed.
         */
        if (desc == NULL)
                goto cleanup;

        /* Append the verity descriptor. */
        err = pagecache_write(inode, desc, desc_size, desc_pos);
        if (err)
                goto cleanup;

        /*
         * Write all pages (both data and verity metadata).  Note that this must
         * happen before clearing FI_VERITY_IN_PROGRESS; otherwise pages beyond
         * i_size won't be written properly.  For crash consistency, this also
         * must happen before the verity inode flag gets persisted.
         */
        err = filemap_write_and_wait(inode->i_mapping);
        if (err)
                goto cleanup;

        /* Set the verity xattr. */
        err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
                            F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
                            NULL, XATTR_CREATE);
        if (err)
                goto cleanup;

        /* Finally, set the verity inode flag. */
        file_set_verity(inode);
        f2fs_set_inode_flags(inode);
        f2fs_mark_inode_dirty_sync(inode, true);

        clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
        return 0;

cleanup:
        /*
         * Verity failed to be enabled, so clean up by truncating any verity
         * metadata that was written beyond i_size (both from cache and from
         * disk) and clearing FI_VERITY_IN_PROGRESS.
         *
         * Taking i_gc_rwsem[WRITE] is needed to stop f2fs garbage collection
         * from re-instantiating cached pages we are truncating (since unlike
         * normal file accesses, garbage collection isn't limited by i_size).
         */
        f2fs_down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
        truncate_inode_pages(inode->i_mapping, inode->i_size);
        err2 = f2fs_truncate(inode);
        if (err2) {
                f2fs_err(sbi, "Truncating verity metadata failed (errno=%d)",
                         err2);
                set_sbi_flag(sbi, SBI_NEED_FSCK);
        }
        f2fs_up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
        clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
        return err ?: err2;
}

static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
                                      size_t buf_size)
{
        struct fsverity_descriptor_location dloc;
        int res;
        u32 size;
        u64 pos;

        /* Get the descriptor location */
        res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
                            F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
        if (res < 0 && res != -ERANGE)
                return res;
        if (res != sizeof(dloc) || dloc.version != cpu_to_le32(F2FS_VERIFY_VER)) {
                f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
                return -EINVAL;
        }
        size = le32_to_cpu(dloc.size);
        pos = le64_to_cpu(dloc.pos);

        /* Get the descriptor */
        if (pos + size < pos ||
            pos + size > F2FS_BLK_TO_BYTES(max_file_blocks(inode)) ||
            pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
                f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
                f2fs_handle_error(F2FS_I_SB(inode),
                                ERROR_CORRUPTED_VERITY_XATTR);
                return -EFSCORRUPTED;
        }
        if (buf_size) {
                if (size > buf_size)
                        return -ERANGE;
                res = pagecache_read(inode, buf, size, pos);
                if (res)
                        return res;
        }
        return size;
}

static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
                                               pgoff_t index)
{
        index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
        return generic_read_merkle_tree_page(inode, index);
}

static void f2fs_readahead_merkle_tree(struct inode *inode, pgoff_t index,
                                       unsigned long nr_pages)
{
        index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
        generic_readahead_merkle_tree(inode, index, nr_pages);
}

static int f2fs_write_merkle_tree_block(struct file *file, const void *buf,
                                        u64 pos, unsigned int size)
{
        pos += f2fs_verity_metadata_pos(file_inode(file));

        return pagecache_write(file_inode(file), buf, size, pos);
}

const struct fsverity_operations f2fs_verityops = {
        .begin_enable_verity    = f2fs_begin_enable_verity,
        .end_enable_verity      = f2fs_end_enable_verity,
        .get_verity_descriptor  = f2fs_get_verity_descriptor,
        .read_merkle_tree_page  = f2fs_read_merkle_tree_page,
        .readahead_merkle_tree  = f2fs_readahead_merkle_tree,
        .write_merkle_tree_block = f2fs_write_merkle_tree_block,
};