// SPDX-License-Identifier: GPL-2.0
#include <linux/fs.h>
#include <linux/random.h>
#include <linux/buffer_head.h>
#include <linux/utsname.h>
#include <linux/kthread.h>

#include "ext4.h"

/* Checksumming functions */
static __le32 ext4_mmp_csum(struct super_block *sb, struct mmp_struct *mmp)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        int offset = offsetof(struct mmp_struct, mmp_checksum);
        __u32 csum;

        csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);

        return cpu_to_le32(csum);
}

static int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
{
        if (!ext4_has_metadata_csum(sb))
                return 1;

        return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
}

static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
{
        if (!ext4_has_metadata_csum(sb))
                return;

        mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
}

/*
 * Write the MMP block using REQ_SYNC to try to get the block on-disk
 * faster.
 */
static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
{
        struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);

        /*
         * We protect against freezing so that we don't create dirty buffers
         * on frozen filesystem.
         */
        sb_start_write(sb);
        ext4_mmp_csum_set(sb, mmp);
        mark_buffer_dirty(bh);
        lock_buffer(bh);
        bh->b_end_io = end_buffer_write_sync;
        get_bh(bh);
        submit_bh(REQ_OP_WRITE, REQ_SYNC | REQ_META | REQ_PRIO, bh);
        wait_on_buffer(bh);
        sb_end_write(sb);
        if (unlikely(!buffer_uptodate(bh)))
                return 1;

        return 0;
}

/*
 * Read the MMP block. It _must_ be read from disk and hence we clear the
 * uptodate flag on the buffer.
 */
static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
                          ext4_fsblk_t mmp_block)
{
        struct mmp_struct *mmp;
        int ret;

        if (*bh)
                clear_buffer_uptodate(*bh);

        /* This would be sb_bread(sb, mmp_block), except we need to be sure
         * that the MD RAID device cache has been bypassed, and that the read
         * is not blocked in the elevator. */
        if (!*bh) {
                *bh = sb_getblk(sb, mmp_block);
                if (!*bh) {
                        ret = -ENOMEM;
                        goto warn_exit;
                }
        }

        get_bh(*bh);
        lock_buffer(*bh);
        (*bh)->b_end_io = end_buffer_read_sync;
        submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO, *bh);
        wait_on_buffer(*bh);
        if (!buffer_uptodate(*bh)) {
                ret = -EIO;
                goto warn_exit;
        }
        mmp = (struct mmp_struct *)((*bh)->b_data);
        if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
                ret = -EFSCORRUPTED;
                goto warn_exit;
        }
        if (!ext4_mmp_csum_verify(sb, mmp)) {
                ret = -EFSBADCRC;
                goto warn_exit;
        }
        return 0;
warn_exit:
        brelse(*bh);
        *bh = NULL;
        ext4_warning(sb, "Error %d while reading MMP block %llu",
                     ret, mmp_block);
        return ret;
}

/*
 * Dump as much information as possible to help the admin.
 */
void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
                    const char *function, unsigned int line, const char *msg)
{
        __ext4_warning(sb, function, line, "%s", msg);
        __ext4_warning(sb, function, line,
                       "MMP failure info: last update time: %llu, last update "
                       "node: %s, last update device: %s",
                       (long long unsigned int) le64_to_cpu(mmp->mmp_time),
                       mmp->mmp_nodename, mmp->mmp_bdevname);
}

/*
 * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
 */
static int kmmpd(void *data)
{
        struct super_block *sb = ((struct mmpd_data *) data)->sb;
        struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
        struct ext4_super_block *es = EXT4_SB(sb)->s_es;
        struct mmp_struct *mmp;
        ext4_fsblk_t mmp_block;
        u32 seq = 0;
        unsigned long failed_writes = 0;
        int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
        unsigned mmp_check_interval;
        unsigned long last_update_time;
        unsigned long diff;
        int retval;

        mmp_block = le64_to_cpu(es->s_mmp_block);
        mmp = (struct mmp_struct *)(bh->b_data);
        mmp->mmp_time = cpu_to_le64(get_seconds());
        /*
         * Start with the higher mmp_check_interval and reduce it if
         * the MMP block is being updated on time.
         */
        mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
                                 EXT4_MMP_MIN_CHECK_INTERVAL);
        mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
        bdevname(bh->b_bdev, mmp->mmp_bdevname);

        memcpy(mmp->mmp_nodename, init_utsname()->nodename,
               sizeof(mmp->mmp_nodename));

        while (!kthread_should_stop()) {
                if (++seq > EXT4_MMP_SEQ_MAX)
                        seq = 1;

                mmp->mmp_seq = cpu_to_le32(seq);
                mmp->mmp_time = cpu_to_le64(get_seconds());
                last_update_time = jiffies;

                retval = write_mmp_block(sb, bh);
                /*
                 * Don't spew too many error messages. Print one every
                 * (s_mmp_update_interval * 60) seconds.
                 */
                if (retval) {
                        if ((failed_writes % 60) == 0)
                                ext4_error(sb, "Error writing to MMP block");
                        failed_writes++;
                }

                if (!(le32_to_cpu(es->s_feature_incompat) &
                    EXT4_FEATURE_INCOMPAT_MMP)) {
                        ext4_warning(sb, "kmmpd being stopped since MMP feature"
                                     " has been disabled.");
                        goto exit_thread;
                }

                if (sb_rdonly(sb)) {
                        ext4_warning(sb, "kmmpd being stopped since filesystem "
                                     "has been remounted as readonly.");
                        goto exit_thread;
                }

                diff = jiffies - last_update_time;
                if (diff < mmp_update_interval * HZ)
                        schedule_timeout_interruptible(mmp_update_interval *
                                                       HZ - diff);

                /*
                 * We need to make sure that more than mmp_check_interval
                 * seconds have not passed since writing. If that has happened
                 * we need to check if the MMP block is as we left it.
                 */
                diff = jiffies - last_update_time;
                if (diff > mmp_check_interval * HZ) {
                        struct buffer_head *bh_check = NULL;
                        struct mmp_struct *mmp_check;

                        retval = read_mmp_block(sb, &bh_check, mmp_block);
                        if (retval) {
                                ext4_error(sb, "error reading MMP data: %d",
                                           retval);
                                goto exit_thread;
                        }

                        mmp_check = (struct mmp_struct *)(bh_check->b_data);
                        if (mmp->mmp_seq != mmp_check->mmp_seq ||
                            memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
                                   sizeof(mmp->mmp_nodename))) {
                                dump_mmp_msg(sb, mmp_check,
                                             "Error while updating MMP info. "
                                             "The filesystem seems to have been"
                                             " multiply mounted.");
                                ext4_error(sb, "abort");
                                put_bh(bh_check);
                                retval = -EBUSY;
                                goto exit_thread;
                        }
                        put_bh(bh_check);
                }

                 /*
                 * Adjust the mmp_check_interval depending on how much time
                 * it took for the MMP block to be written.
                 */
                mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
                                             EXT4_MMP_MAX_CHECK_INTERVAL),
                                         EXT4_MMP_MIN_CHECK_INTERVAL);
                mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
        }

        /*
         * Unmount seems to be clean.
         */
        mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
        mmp->mmp_time = cpu_to_le64(get_seconds());

        retval = write_mmp_block(sb, bh);

exit_thread:
        EXT4_SB(sb)->s_mmp_tsk = NULL;
        kfree(data);
        brelse(bh);
        return retval;
}

/*
 * Get a random new sequence number but make sure it is not greater than
 * EXT4_MMP_SEQ_MAX.
 */
static unsigned int mmp_new_seq(void)
{
        u32 new_seq;

        do {
                new_seq = prandom_u32();
        } while (new_seq > EXT4_MMP_SEQ_MAX);

        return new_seq;
}

/*
 * Protect the filesystem from being mounted more than once.
 */
int ext4_multi_mount_protect(struct super_block *sb,
                                    ext4_fsblk_t mmp_block)
{
        struct ext4_super_block *es = EXT4_SB(sb)->s_es;
        struct buffer_head *bh = NULL;
        struct mmp_struct *mmp = NULL;
        struct mmpd_data *mmpd_data;
        u32 seq;
        unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
        unsigned int wait_time = 0;
        int retval;

        if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
            mmp_block >= ext4_blocks_count(es)) {
                ext4_warning(sb, "Invalid MMP block in superblock");
                goto failed;
        }

        retval = read_mmp_block(sb, &bh, mmp_block);
        if (retval)
                goto failed;

        mmp = (struct mmp_struct *)(bh->b_data);

        if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
                mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;

        /*
         * If check_interval in MMP block is larger, use that instead of
         * update_interval from the superblock.
         */
        if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
                mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);

        seq = le32_to_cpu(mmp->mmp_seq);
        if (seq == EXT4_MMP_SEQ_CLEAN)
                goto skip;

        if (seq == EXT4_MMP_SEQ_FSCK) {
                dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
                goto failed;
        }

        wait_time = min(mmp_check_interval * 2 + 1,
                        mmp_check_interval + 60);

        /* Print MMP interval if more than 20 secs. */
        if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
                ext4_warning(sb, "MMP interval %u higher than expected, please"
                             " wait.\n", wait_time * 2);

        if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
                ext4_warning(sb, "MMP startup interrupted, failing mount\n");
                goto failed;
        }

        retval = read_mmp_block(sb, &bh, mmp_block);
        if (retval)
                goto failed;
        mmp = (struct mmp_struct *)(bh->b_data);
        if (seq != le32_to_cpu(mmp->mmp_seq)) {
                dump_mmp_msg(sb, mmp,
                             "Device is already active on another node.");
                goto failed;
        }

skip:
        /*
         * write a new random sequence number.
         */
        seq = mmp_new_seq();
        mmp->mmp_seq = cpu_to_le32(seq);

        retval = write_mmp_block(sb, bh);
        if (retval)
                goto failed;

        /*
         * wait for MMP interval and check mmp_seq.
         */
        if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
                ext4_warning(sb, "MMP startup interrupted, failing mount");
                goto failed;
        }

        retval = read_mmp_block(sb, &bh, mmp_block);
        if (retval)
                goto failed;
        mmp = (struct mmp_struct *)(bh->b_data);
        if (seq != le32_to_cpu(mmp->mmp_seq)) {
                dump_mmp_msg(sb, mmp,
                             "Device is already active on another node.");
                goto failed;
        }

        mmpd_data = kmalloc(sizeof(*mmpd_data), GFP_KERNEL);
        if (!mmpd_data) {
                ext4_warning(sb, "not enough memory for mmpd_data");
                goto failed;
        }
        mmpd_data->sb = sb;
        mmpd_data->bh = bh;

        /*
         * Start a kernel thread to update the MMP block periodically.
         */
        EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%s",
                                             bdevname(bh->b_bdev,
                                                      mmp->mmp_bdevname));
        if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
                EXT4_SB(sb)->s_mmp_tsk = NULL;
                kfree(mmpd_data);
                ext4_warning(sb, "Unable to create kmmpd thread for %s.",
                             sb->s_id);
                goto failed;
        }

        return 0;

failed:
        brelse(bh);
        return 1;
}