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    Subject[PATCH 14/23] ext4: Add checksums to the MMP block
    From
    Date
    Compute and verify a checksum for the MMP block.

    Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
    ---
    fs/ext4/ext4.h | 3 +++
    fs/ext4/mmp.c | 44 +++++++++++++++++++++++++++++++++++++++-----
    2 files changed, 42 insertions(+), 5 deletions(-)


    diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
    index e24386f..325bae0 100644
    --- a/fs/ext4/ext4.h
    +++ b/fs/ext4/ext4.h
    @@ -2378,6 +2378,9 @@ extern int ext4_bio_write_page(struct ext4_io_submit *io,

    /* mmp.c */
    extern int ext4_multi_mount_protect(struct super_block *, ext4_fsblk_t);
    +extern void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp);
    +extern int ext4_mmp_csum_verify(struct super_block *sb,
    + struct mmp_struct *mmp);

    /* BH_Uninit flag: blocks are allocated but uninitialized on disk */
    enum ext4_state_bits {
    diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
    index 7ea4ba4..142e9d7 100644
    --- a/fs/ext4/mmp.c
    +++ b/fs/ext4/mmp.c
    @@ -6,12 +6,45 @@

    #include "ext4.h"

    +/* Checksumming functions */
    +static __u32 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);
    +}
    +
    +int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
    +{
    + if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
    + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
    + return 1;
    +
    + return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
    +}
    +
    +void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
    +{
    + if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
    + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
    + return;
    +
    + mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
    +}
    +
    /*
    * Write the MMP block using WRITE_SYNC to try to get the block on-disk
    * faster.
    */
    -static int write_mmp_block(struct buffer_head *bh)
    +static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
    {
    + struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);
    +
    + ext4_mmp_csum_set(sb, mmp);
    mark_buffer_dirty(bh);
    lock_buffer(bh);
    bh->b_end_io = end_buffer_write_sync;
    @@ -59,7 +92,8 @@ static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
    }

    mmp = (struct mmp_struct *)((*bh)->b_data);
    - if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC)
    + if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC ||
    + !ext4_mmp_csum_verify(sb, mmp))
    return -EINVAL;

    return 0;
    @@ -120,7 +154,7 @@ static int kmmpd(void *data)
    mmp->mmp_time = cpu_to_le64(get_seconds());
    last_update_time = jiffies;

    - retval = write_mmp_block(bh);
    + retval = write_mmp_block(sb, bh);
    /*
    * Don't spew too many error messages. Print one every
    * (s_mmp_update_interval * 60) seconds.
    @@ -200,7 +234,7 @@ static int kmmpd(void *data)
    mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
    mmp->mmp_time = cpu_to_le64(get_seconds());

    - retval = write_mmp_block(bh);
    + retval = write_mmp_block(sb, bh);

    failed:
    kfree(data);
    @@ -299,7 +333,7 @@ skip:
    seq = mmp_new_seq();
    mmp->mmp_seq = cpu_to_le32(seq);

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



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