Re: [PATCH 2/2] ext4: Spot-check block group sub-table locations

[Zheng Liu <gnehzuil.liu@gmail.com>]

On Thu, Sep 26, 2013 at 05:03:34PM -0700, Darrick J. Wong wrote:
> Perform a quick sanity check of bitmap and inode table block numbers when
> loading them, and if there's something suspicious, mark the block group
> corrupt.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/ext4/balloc.c |    5 +++++
>  fs/ext4/ext4.h   |    2 ++
>  fs/ext4/ialloc.c |    4 ++++
>  fs/ext4/inode.c  |    6 ++++++
>  fs/ext4/super.c  |   21 +++++++++++++++++++++
>  5 files changed, 38 insertions(+)
> 
> 
> diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> index 4390f9f..3d79bfe 100644
> --- a/fs/ext4/balloc.c
> +++ b/fs/ext4/balloc.c
> @@ -396,11 +396,16 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
>  	struct ext4_group_desc *desc;
>  	struct buffer_head *bh;
>  	ext4_fsblk_t bitmap_blk;
> +	struct ext4_group_info *grp;
>  
>  	desc = ext4_get_group_desc(sb, block_group, NULL);
>  	if (!desc)
>  		return NULL;
>  	bitmap_blk = ext4_block_bitmap(sb, desc);
> +	if (!ext4_is_sane_bgdata_location(sb, block_group, bitmap_blk)) {
> +		grp = ext4_get_group_info(sb, block_group);
> +		set_bit(EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT, &grp->bb_state);

Why don't return NULL directly?  If we found that the location of bitmap
is insane, we shouldn't read this bitmap.

                                                - Zheng

> +	}
>  	bh = sb_getblk(sb, bitmap_blk);
>  	if (unlikely(!bh)) {
>  		ext4_error(sb, "Cannot get buffer for block bitmap - "
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index af815ea..afb1bb2 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2531,6 +2531,8 @@ static inline void ext4_unlock_group(struct super_block *sb,
>  	spin_unlock(ext4_group_lock_ptr(sb, group));
>  }
>  
> +int ext4_is_sane_bgdata_location(struct super_block *sb, ext4_group_t grp,
> +				 ext4_fsblk_t blk);
>  /*
>   * Block validity checking
>   */
> diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
> index 137193f..242250d 100644
> --- a/fs/ext4/ialloc.c
> +++ b/fs/ext4/ialloc.c
> @@ -122,6 +122,10 @@ ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
>  		return NULL;
>  
>  	bitmap_blk = ext4_inode_bitmap(sb, desc);
> +	if (!ext4_is_sane_bgdata_location(sb, block_group, bitmap_blk)) {
> +		grp = ext4_get_group_info(sb, block_group);
> +		set_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT, &grp->bb_state);
> +	}
>  	bh = sb_getblk(sb, bitmap_blk);
>  	if (unlikely(!bh)) {
>  		ext4_error(sb, "Cannot read inode bitmap - "
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0d424d7..c5af22e 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3795,6 +3795,7 @@ static int __ext4_get_inode_loc(struct inode *inode,
>  	struct super_block	*sb = inode->i_sb;
>  	ext4_fsblk_t		block;
>  	int			inodes_per_block, inode_offset;
> +	struct ext4_group_info	*grp;
>  
>  	iloc->bh = NULL;
>  	if (!ext4_valid_inum(sb, inode->i_ino))
> @@ -3814,6 +3815,11 @@ static int __ext4_get_inode_loc(struct inode *inode,
>  	block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
>  	iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);
>  
> +	if (!ext4_is_sane_bgdata_location(sb, iloc->block_group, block)) {
> +		grp = ext4_get_group_info(sb, iloc->block_group);
> +		set_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT, &grp->bb_state);
> +		return -EIO;
> +	}
>  	bh = sb_getblk(sb, block);
>  	if (unlikely(!bh))
>  		return -ENOMEM;
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 2c2e6cb..d22248e 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -2049,6 +2049,27 @@ void ext4_group_desc_csum_set(struct super_block *sb, __u32 block_group,
>  	gdp->bg_checksum = ext4_group_desc_csum(EXT4_SB(sb), block_group, gdp);
>  }
>  
> +/* returns 1 if the location of a blockgroup data item seems sane */
> +int ext4_is_sane_bgdata_location(struct super_block *sb, ext4_group_t grp,
> +				 ext4_fsblk_t blk)
> +{
> +	struct ext4_sb_info *sbi = EXT4_SB(sb);
> +	ext4_fsblk_t first_block = le32_to_cpu(sbi->s_es->s_first_data_block);
> +	ext4_fsblk_t last_block;
> +
> +	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG))
> +		last_block = ext4_blocks_count(sbi->s_es) - 1;
> +	else {
> +		first_block += grp * sbi->s_blocks_per_group;
> +		last_block = first_block + (EXT4_BLOCKS_PER_GROUP(sb) - 1);
> +	}
> +
> +	if (last_block >= ext4_blocks_count(sbi->s_es))
> +		last_block = ext4_blocks_count(sbi->s_es) - 1;
> +
> +	return blk >= first_block && blk <= last_block;
> +}
> +
>  /* Called at mount-time, super-block is locked */
>  static int ext4_check_descriptors(struct super_block *sb,
>  				  ext4_group_t *first_not_zeroed)
> 
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