// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/ext4/block_validity.c
 *
 * Copyright (C) 2009
 * Theodore Ts'o (tytso@mit.edu)
 *
 * Track which blocks in the filesystem are metadata blocks that
 * should never be used as data blocks by files or directories.
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/quotaops.h>
#include <linux/buffer_head.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include "ext4.h"

struct ext4_system_zone {
        struct rb_node  node;
        ext4_fsblk_t    start_blk;
        unsigned int    count;
};

static struct kmem_cache *ext4_system_zone_cachep;

int __init ext4_init_system_zone(void)
{
        ext4_system_zone_cachep = KMEM_CACHE(ext4_system_zone, 0);
        if (ext4_system_zone_cachep == NULL)
                return -ENOMEM;
        return 0;
}

void ext4_exit_system_zone(void)
{
        rcu_barrier();
        kmem_cache_destroy(ext4_system_zone_cachep);
}

static inline int can_merge(struct ext4_system_zone *entry1,
                     struct ext4_system_zone *entry2)
{
        if ((entry1->start_blk + entry1->count) == entry2->start_blk)
                return 1;
        return 0;
}

static void release_system_zone(struct ext4_system_blocks *system_blks)
{
        struct ext4_system_zone *entry, *n;

        rbtree_postorder_for_each_entry_safe(entry, n,
                                &system_blks->root, node)
                kmem_cache_free(ext4_system_zone_cachep, entry);
}

/*
 * Mark a range of blocks as belonging to the "system zone" --- that
 * is, filesystem metadata blocks which should never be used by
 * inodes.
 */
static int add_system_zone(struct ext4_system_blocks *system_blks,
                           ext4_fsblk_t start_blk,
                           unsigned int count)
{
        struct ext4_system_zone *new_entry = NULL, *entry;
        struct rb_node **n = &system_blks->root.rb_node, *node;
        struct rb_node *parent = NULL, *new_node = NULL;

        while (*n) {
                parent = *n;
                entry = rb_entry(parent, struct ext4_system_zone, node);
                if (start_blk < entry->start_blk)
                        n = &(*n)->rb_left;
                else if (start_blk >= (entry->start_blk + entry->count))
                        n = &(*n)->rb_right;
                else {
                        if (start_blk + count > (entry->start_blk +
                                                 entry->count))
                                entry->count = (start_blk + count -
                                                entry->start_blk);
                        new_node = *n;
                        new_entry = rb_entry(new_node, struct ext4_system_zone,
                                             node);
                        break;
                }
        }

        if (!new_entry) {
                new_entry = kmem_cache_alloc(ext4_system_zone_cachep,
                                             GFP_KERNEL);
                if (!new_entry)
                        return -ENOMEM;
                new_entry->start_blk = start_blk;
                new_entry->count = count;
                new_node = &new_entry->node;

                rb_link_node(new_node, parent, n);
                rb_insert_color(new_node, &system_blks->root);
        }

        /* Can we merge to the left? */
        node = rb_prev(new_node);
        if (node) {
                entry = rb_entry(node, struct ext4_system_zone, node);
                if (can_merge(entry, new_entry)) {
                        new_entry->start_blk = entry->start_blk;
                        new_entry->count += entry->count;
                        rb_erase(node, &system_blks->root);
                        kmem_cache_free(ext4_system_zone_cachep, entry);
                }
        }

        /* Can we merge to the right? */
        node = rb_next(new_node);
        if (node) {
                entry = rb_entry(node, struct ext4_system_zone, node);
                if (can_merge(new_entry, entry)) {
                        new_entry->count += entry->count;
                        rb_erase(node, &system_blks->root);
                        kmem_cache_free(ext4_system_zone_cachep, entry);
                }
        }
        return 0;
}

static void debug_print_tree(struct ext4_sb_info *sbi)
{
        struct rb_node *node;
        struct ext4_system_zone *entry;
        struct ext4_system_blocks *system_blks;
        int first = 1;

        printk(KERN_INFO "System zones: ");
        rcu_read_lock();
        system_blks = rcu_dereference(sbi->system_blks);
        node = rb_first(&system_blks->root);
        while (node) {
                entry = rb_entry(node, struct ext4_system_zone, node);
                printk(KERN_CONT "%s%llu-%llu", first ? "" : ", ",
                       entry->start_blk, entry->start_blk + entry->count - 1);
                first = 0;
                node = rb_next(node);
        }
        rcu_read_unlock();
        printk(KERN_CONT "\n");
}

/*
 * Returns 1 if the passed-in block region (start_blk,
 * start_blk+count) is valid; 0 if some part of the block region
 * overlaps with filesystem metadata blocks.
 */
static int ext4_data_block_valid_rcu(struct ext4_sb_info *sbi,
                                     struct ext4_system_blocks *system_blks,
                                     ext4_fsblk_t start_blk,
                                     unsigned int count)
{
        struct ext4_system_zone *entry;
        struct rb_node *n;

        if ((start_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
            (start_blk + count < start_blk) ||
            (start_blk + count > ext4_blocks_count(sbi->s_es)))
                return 0;

        if (system_blks == NULL)
                return 1;

        n = system_blks->root.rb_node;
        while (n) {
                entry = rb_entry(n, struct ext4_system_zone, node);
                if (start_blk + count - 1 < entry->start_blk)
                        n = n->rb_left;
                else if (start_blk >= (entry->start_blk + entry->count))
                        n = n->rb_right;
                else
                        return 0;
        }
        return 1;
}

static int ext4_protect_reserved_inode(struct super_block *sb,
                                       struct ext4_system_blocks *system_blks,
                                       u32 ino)
{
        struct inode *inode;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_map_blocks map;
        u32 i = 0, num;
        int err = 0, n;

        if ((ino < EXT4_ROOT_INO) ||
            (ino > le32_to_cpu(sbi->s_es->s_inodes_count)))
                return -EINVAL;
        inode = ext4_iget(sb, ino, EXT4_IGET_SPECIAL);
        if (IS_ERR(inode))
                return PTR_ERR(inode);
        num = (inode->i_size + sb->s_blocksize - 1) >> sb->s_blocksize_bits;
        while (i < num) {
                cond_resched();
                map.m_lblk = i;
                map.m_len = num - i;
                n = ext4_map_blocks(NULL, inode, &map, 0);
                if (n < 0) {
                        err = n;
                        break;
                }
                if (n == 0) {
                        i++;
                } else {
                        if (!ext4_data_block_valid_rcu(sbi, system_blks,
                                                map.m_pblk, n)) {
                                err = -EFSCORRUPTED;
                                __ext4_error(sb, __func__, __LINE__, -err,
                                             map.m_pblk, "blocks %llu-%llu "
                                             "from inode %u overlap system zone",
                                             map.m_pblk,
                                             map.m_pblk + map.m_len - 1, ino);
                                break;
                        }
                        err = add_system_zone(system_blks, map.m_pblk, n);
                        if (err < 0)
                                break;
                        i += n;
                }
        }
        iput(inode);
        return err;
}

static void ext4_destroy_system_zone(struct rcu_head *rcu)
{
        struct ext4_system_blocks *system_blks;

        system_blks = container_of(rcu, struct ext4_system_blocks, rcu);
        release_system_zone(system_blks);
        kfree(system_blks);
}

/*
 * Build system zone rbtree which is used for block validity checking.
 *
 * The update of system_blks pointer in this function is protected by
 * sb->s_umount semaphore. However we have to be careful as we can be
 * racing with ext4_data_block_valid() calls reading system_blks rbtree
 * protected only by RCU. That's why we first build the rbtree and then
 * swap it in place.
 */
int ext4_setup_system_zone(struct super_block *sb)
{
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_system_blocks *system_blks;
        struct ext4_group_desc *gdp;
        ext4_group_t i;
        int flex_size = ext4_flex_bg_size(sbi);
        int ret;

        if (!test_opt(sb, BLOCK_VALIDITY)) {
                if (sbi->system_blks)
                        ext4_release_system_zone(sb);
                return 0;
        }
        if (sbi->system_blks)
                return 0;

        system_blks = kzalloc(sizeof(*system_blks), GFP_KERNEL);
        if (!system_blks)
                return -ENOMEM;

        for (i=0; i < ngroups; i++) {
                cond_resched();
                if (ext4_bg_has_super(sb, i) &&
                    ((i < 5) || ((i % flex_size) == 0)))
                        add_system_zone(system_blks,
                                        ext4_group_first_block_no(sb, i),
                                        ext4_bg_num_gdb(sb, i) + 1);
                gdp = ext4_get_group_desc(sb, i, NULL);
                ret = add_system_zone(system_blks,
                                ext4_block_bitmap(sb, gdp), 1);
                if (ret)
                        goto err;
                ret = add_system_zone(system_blks,
                                ext4_inode_bitmap(sb, gdp), 1);
                if (ret)
                        goto err;
                ret = add_system_zone(system_blks,
                                ext4_inode_table(sb, gdp),
                                sbi->s_itb_per_group);
                if (ret)
                        goto err;
        }
        if (ext4_has_feature_journal(sb) && sbi->s_es->s_journal_inum) {
                ret = ext4_protect_reserved_inode(sb, system_blks,
                                le32_to_cpu(sbi->s_es->s_journal_inum));
                if (ret)
                        goto err;
        }

        /*
         * System blks rbtree complete, announce it once to prevent racing
         * with ext4_data_block_valid() accessing the rbtree at the same
         * time.
         */
        rcu_assign_pointer(sbi->system_blks, system_blks);

        if (test_opt(sb, DEBUG))
                debug_print_tree(sbi);
        return 0;
err:
        release_system_zone(system_blks);
        kfree(system_blks);
        return ret;
}

/*
 * Called when the filesystem is unmounted or when remounting it with
 * noblock_validity specified.
 *
 * The update of system_blks pointer in this function is protected by
 * sb->s_umount semaphore. However we have to be careful as we can be
 * racing with ext4_data_block_valid() calls reading system_blks rbtree
 * protected only by RCU. So we first clear the system_blks pointer and
 * then free the rbtree only after RCU grace period expires.
 */
void ext4_release_system_zone(struct super_block *sb)
{
        struct ext4_system_blocks *system_blks;

        system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks,
                                        lockdep_is_held(&sb->s_umount));
        rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL);

        if (system_blks)
                call_rcu(&system_blks->rcu, ext4_destroy_system_zone);
}

int ext4_data_block_valid(struct ext4_sb_info *sbi, ext4_fsblk_t start_blk,
                          unsigned int count)
{
        struct ext4_system_blocks *system_blks;
        int ret;

        /*
         * Lock the system zone to prevent it being released concurrently
         * when doing a remount which inverse current "[no]block_validity"
         * mount option.
         */
        rcu_read_lock();
        system_blks = rcu_dereference(sbi->system_blks);
        ret = ext4_data_block_valid_rcu(sbi, system_blks, start_blk,
                                        count);
        rcu_read_unlock();
        return ret;
}

int ext4_check_blockref(const char *function, unsigned int line,
                        struct inode *inode, __le32 *p, unsigned int max)
{
        __le32 *bref = p;
        unsigned int blk;

        if (ext4_has_feature_journal(inode->i_sb) &&
            (inode->i_ino ==
             le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_journal_inum)))
                return 0;

        while (bref < p+max) {
                blk = le32_to_cpu(*bref++);
                if (blk &&
                    unlikely(!ext4_data_block_valid(EXT4_SB(inode->i_sb),
                                                    blk, 1))) {
                        ext4_error_inode(inode, function, line, blk,
                                         "invalid block");
                        return -EFSCORRUPTED;
                }
        }
        return 0;
}