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Commit abcb2947 authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Theodore Ts'o
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ext4: add block bitmap validation 



When a new block bitmap is read from disk in read_block_bitmap()
there are a few bits that should ALWAYS be set.  In particular,
the blocks given corresponding to block bitmap, inode bitmap and inode tables.
Validate the block bitmap against these blocks.

Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
parent 389d1b08

fs/ext4/balloc.c

+81 −18
Original line number Diff line number Diff line
@@ -189,13 +189,65 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block * sb, 
	return desc;

}



static int ext4_valid_block_bitmap(struct super_block *sb,

					struct ext4_group_desc *desc,

					unsigned int block_group,

					struct buffer_head *bh)

{

	ext4_grpblk_t offset;

	ext4_grpblk_t next_zero_bit;

	ext4_fsblk_t bitmap_blk;

	ext4_fsblk_t group_first_block;



	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {

		/* with FLEX_BG, the inode/block bitmaps and itable

		 * blocks may not be in the group at all

		 * so the bitmap validation will be skipped for those groups

		 * or it has to also read the block group where the bitmaps

		 * are located to verify they are set.

		 */

		return 1;

	}

	group_first_block = ext4_group_first_block_no(sb, block_group);



	/* check whether block bitmap block number is set */

	bitmap_blk = ext4_block_bitmap(sb, desc);

	offset = bitmap_blk - group_first_block;

	if (!ext4_test_bit(offset, bh->b_data))

		/* bad block bitmap */

		goto err_out;



	/* check whether the inode bitmap block number is set */

	bitmap_blk = ext4_inode_bitmap(sb, desc);

	offset = bitmap_blk - group_first_block;

	if (!ext4_test_bit(offset, bh->b_data))

		/* bad block bitmap */

		goto err_out;



	/* check whether the inode table block number is set */

	bitmap_blk = ext4_inode_table(sb, desc);

	offset = bitmap_blk - group_first_block;

	next_zero_bit = ext4_find_next_zero_bit(bh->b_data,

				offset + EXT4_SB(sb)->s_itb_per_group,

				offset);

	if (next_zero_bit >= offset + EXT4_SB(sb)->s_itb_per_group)

		/* good bitmap for inode tables */

		return 1;



err_out:

	ext4_error(sb, __FUNCTION__,

			"Invalid block bitmap - "

			"block_group = %d, block = %llu",

			block_group, bitmap_blk);

	return 0;

}

/**

 * read_block_bitmap()

 * @sb:			super block

 * @block_group:	given block group

 *

 * Read the bitmap for a given block_group, reading into the specified

 * slot in the superblock's bitmap cache.

 * Read the bitmap for a given block_group,and validate the

 * bits for block/inode/inode tables are set in the bitmaps

 *

 * Return buffer_head on success or NULL in case of failure.

 */
@@ -210,25 +262,36 @@ read_block_bitmap(struct super_block *sb, ext4_group_t block_group) 
	if (!desc)

		return NULL;

	bitmap_blk = ext4_block_bitmap(sb, desc);

	if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {

	bh = sb_getblk(sb, bitmap_blk);

		if (!buffer_uptodate(bh)) {

			lock_buffer(bh);

			if (!buffer_uptodate(bh)) {

				ext4_init_block_bitmap(sb, bh, block_group,

						       desc);

				set_buffer_uptodate(bh);

	if (unlikely(!bh)) {

		ext4_error(sb, __FUNCTION__,

			    "Cannot read block bitmap - "

			    "block_group = %d, block_bitmap = %llu",

			    (int)block_group, (unsigned long long)bitmap_blk);

		return NULL;

	}

	if (bh_uptodate_or_lock(bh))

		return bh;



	if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {

		ext4_init_block_bitmap(sb, bh, block_group, desc);

		set_buffer_uptodate(bh);

		unlock_buffer(bh);

		return bh;

	}

	} else {

		bh = sb_bread(sb, bitmap_blk);

	}

	if (!bh)

	if (bh_submit_read(bh) < 0) {

		put_bh(bh);

		ext4_error(sb, __FUNCTION__,

			    "Cannot read block bitmap - "

			    "block_group = %lu, block_bitmap = %llu",

			    block_group, bitmap_blk);

			    "block_group = %d, block_bitmap = %llu",

			    (int)block_group, (unsigned long long)bitmap_blk);

		return NULL;

	}

	if (!ext4_valid_block_bitmap(sb, desc, block_group, bh)) {

		put_bh(bh);

		return NULL;

	}



	return bh;

}

/*