// SPDX-License-Identifier: GPL-2.0
/*
 * fs/ext4/verity.c: fs-verity support for ext4
 *
 * Copyright 2019 Google LLC
 */

/*
 * Implementation of fsverity_operations for ext4.
 *
 * ext4 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 ext4 with only some relatively small changes to ext4.  This approach
 * avoids having to depend on the EA_INODE feature and on rearchitecturing
 * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and
 * to support encrypting xattrs.  Note that the verity metadata *must* be
 * encrypted when the file is, since 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/quotaops.h>

#include "ext4.h"
#include "ext4_extents.h"
#include "ext4_jbd2.h"

static inline loff_t ext4_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;
                void *addr;

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

                addr = kmap_atomic(page);
                memcpy(buf, addr + offset_in_page(pos), n);
                kunmap_atomic(addr);

                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)
{
        if (pos + count > inode->i_sb->s_maxbytes)
                return -EFBIG;

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

                res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
                                            &page, &fsdata);
                if (res)
                        return res;

                addr = kmap_atomic(page);
                memcpy(addr + offset_in_page(pos), buf, n);
                kunmap_atomic(addr);

                res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
                                          page, fsdata);
                if (res < 0)
                        return res;
                if (res != n)
                        return -EIO;

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

static int ext4_begin_enable_verity(struct file *filp)
{
        struct inode *inode = file_inode(filp);
        const int credits = 2; /* superblock and inode for ext4_orphan_add() */
        handle_t *handle;
        int err;

        if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX))
                return -EINVAL;

        if (ext4_verity_in_progress(inode))
                return -EBUSY;

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

        err = ext4_inode_attach_jinode(inode);
        if (err)
                return err;

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

        err = ext4_convert_inline_data(inode);
        if (err)
                return err;

        if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                ext4_warning_inode(inode,
                                   "verity is only allowed on extent-based files");
                return -EOPNOTSUPP;
        }

        /*
         * ext4 uses the last allocated block to find the verity descriptor, so
         * we must remove any other blocks past EOF which might confuse things.
         */
        err = ext4_truncate(inode);
        if (err)
                return err;

        handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
        if (IS_ERR(handle))
                return PTR_ERR(handle);

        err = ext4_orphan_add(handle, inode);
        if (err == 0)
                ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);

        ext4_journal_stop(handle);
        return err;
}

/*
 * ext4 stores the verity descriptor beginning on the next filesystem block
 * boundary after the Merkle tree.  Then, the descriptor size is stored in the
 * last 4 bytes of the last allocated filesystem block --- which is either the
 * block in which the descriptor ends, or the next block after that if there
 * weren't at least 4 bytes remaining.
 *
 * We can't simply store the descriptor in an xattr because it *must* be
 * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
 * xattrs.  Also, if the descriptor includes a large signature blob it may be
 * too large to store in an xattr without the EA_INODE feature.
 */
static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
                                        size_t desc_size, u64 merkle_tree_size)
{
        const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
                                      merkle_tree_size, i_blocksize(inode));
        const u64 desc_end = desc_pos + desc_size;
        const __le32 desc_size_disk = cpu_to_le32(desc_size);
        const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
                                           i_blocksize(inode)) -
                                  sizeof(desc_size_disk);
        int err;

        err = pagecache_write(inode, desc, desc_size, desc_pos);
        if (err)
                return err;

        return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
                               desc_size_pos);
}

static int ext4_end_enable_verity(struct file *filp, const void *desc,
                                  size_t desc_size, u64 merkle_tree_size)
{
        struct inode *inode = file_inode(filp);
        const int credits = 2; /* superblock and inode for ext4_orphan_del() */
        handle_t *handle;
        int err = 0;
        int err2;

        if (desc != NULL) {
                /* Succeeded; write the verity descriptor. */
                err = ext4_write_verity_descriptor(inode, desc, desc_size,
                                                   merkle_tree_size);

                /* Write all pages before clearing VERITY_IN_PROGRESS. */
                if (!err)
                        err = filemap_write_and_wait(inode->i_mapping);
        }

        /* If we failed, truncate anything we wrote past i_size. */
        if (desc == NULL || err)
                ext4_truncate(inode);

        /*
         * We must always clean up by clearing EXT4_STATE_VERITY_IN_PROGRESS and
         * deleting the inode from the orphan list, even if something failed.
         * If everything succeeded, we'll also set the verity bit in the same
         * transaction.
         */

        ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);

        handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
        if (IS_ERR(handle)) {
                ext4_orphan_del(NULL, inode);
                return PTR_ERR(handle);
        }

        err2 = ext4_orphan_del(handle, inode);
        if (err2)
                goto out_stop;

        if (desc != NULL && !err) {
                struct ext4_iloc iloc;

                err = ext4_reserve_inode_write(handle, inode, &iloc);
                if (err)
                        goto out_stop;
                ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
                ext4_set_inode_flags(inode, false);
                err = ext4_mark_iloc_dirty(handle, inode, &iloc);
        }
out_stop:
        ext4_journal_stop(handle);
        return err ?: err2;
}

static int ext4_get_verity_descriptor_location(struct inode *inode,
                                               size_t *desc_size_ret,
                                               u64 *desc_pos_ret)
{
        struct ext4_ext_path *path;
        struct ext4_extent *last_extent;
        u32 end_lblk;
        u64 desc_size_pos;
        __le32 desc_size_disk;
        u32 desc_size;
        u64 desc_pos;
        int err;

        /*
         * Descriptor size is in last 4 bytes of last allocated block.
         * See ext4_write_verity_descriptor().
         */

        if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
                return -EFSCORRUPTED;
        }

        path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
        if (IS_ERR(path))
                return PTR_ERR(path);

        last_extent = path[path->p_depth].p_ext;
        if (!last_extent) {
                EXT4_ERROR_INODE(inode, "verity file has no extents");
                ext4_ext_drop_refs(path);
                kfree(path);
                return -EFSCORRUPTED;
        }

        end_lblk = le32_to_cpu(last_extent->ee_block) +
                   ext4_ext_get_actual_len(last_extent);
        desc_size_pos = (u64)end_lblk << inode->i_blkbits;
        ext4_ext_drop_refs(path);
        kfree(path);

        if (desc_size_pos < sizeof(desc_size_disk))
                goto bad;
        desc_size_pos -= sizeof(desc_size_disk);

        err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
                             desc_size_pos);
        if (err)
                return err;
        desc_size = le32_to_cpu(desc_size_disk);

        /*
         * The descriptor is stored just before the desc_size_disk, but starting
         * on a filesystem block boundary.
         */

        if (desc_size > INT_MAX || desc_size > desc_size_pos)
                goto bad;

        desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
        if (desc_pos < ext4_verity_metadata_pos(inode))
                goto bad;

        *desc_size_ret = desc_size;
        *desc_pos_ret = desc_pos;
        return 0;

bad:
        EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
        return -EFSCORRUPTED;
}

static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
                                      size_t buf_size)
{
        size_t desc_size = 0;
        u64 desc_pos = 0;
        int err;

        err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
        if (err)
                return err;

        if (buf_size) {
                if (desc_size > buf_size)
                        return -ERANGE;
                err = pagecache_read(inode, buf, desc_size, desc_pos);
                if (err)
                        return err;
        }
        return desc_size;
}

static struct page *ext4_read_merkle_tree_page(struct inode *inode,
                                               pgoff_t index,
                                               unsigned long num_ra_pages)
{
        DEFINE_READAHEAD(ractl, NULL, inode->i_mapping, index);
        struct page *page;

        index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;

        page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
        if (!page || !PageUptodate(page)) {
                if (page)
                        put_page(page);
                else if (num_ra_pages > 1)
                        page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
                page = read_mapping_page(inode->i_mapping, index, NULL);
        }
        return page;
}

static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
                                        u64 index, int log_blocksize)
{
        loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize);

        return pagecache_write(inode, buf, 1 << log_blocksize, pos);
}

const struct fsverity_operations ext4_verityops = {
        .begin_enable_verity    = ext4_begin_enable_verity,
        .end_enable_verity      = ext4_end_enable_verity,
        .get_verity_descriptor  = ext4_get_verity_descriptor,
        .read_merkle_tree_page  = ext4_read_merkle_tree_page,
        .write_merkle_tree_block = ext4_write_merkle_tree_block,
};