Andreas Dilger wrote:
During a discussion at OLS, I came up with a very simple way of validating
the ext2/3/4 block bitmaps at read time. Until such a time when we have
checksums for the bitmaps we can have a simple but quite robust mechanism
that is useful for ext2/3/4.
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 by
desc->bg_block_bitmap, desc->bg_inode_bitmap, and the inode table in
[desc->bg_inode_table, +sbi->s_itb_per_group]. If those bits (shifted to be
relative to the current group, of course) are not set then the on-disk group
descriptor is corrupt, or there is some problem reading it from disk, and
this needs to generate an extN_error() call[*] to make the fs read-only.
A similar check can be done with the inode bitmap - it should have the
bits at the end of each bitmap set, for bits higher than s_inodes_per_group.
Something like this ?. If yes i can send a patch with full changelog
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 44c6254..b9a334c 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -115,17 +115,50 @@ read_block_bitmap(struct super_block *sb, unsigned int block_group)
{
struct ext4_group_desc * desc;
struct buffer_head * bh = NULL;
+ ext4_fsblk_t bitmap_blk, grp_rel_blk, grp_first_blk;
desc = ext4_get_group_desc (sb, block_group, NULL);
if (!desc)
goto error_out;
- bh = sb_bread(sb, ext4_block_bitmap(sb, desc));
+ bitmap_blk = ext4_block_bitmap(sb, desc);
+ bh = sb_bread(sb, bitmap_blk);
if (!bh)
ext4_error (sb, "read_block_bitmap",
"Cannot read block bitmap - "
"block_group = %d, block_bitmap = %llu",
- block_group,
- ext4_block_bitmap(sb, desc));
+ block_group, bitmap_blk);
+
+ /* check whether block bitmap block number is set */
+ printk("blk bitmap = %llu first block = %llu block group = %u \n",
+ bitmap_blk, ext4_group_first_block_no(sb, block_group),
+ block_group);
+
+ grp_first_blk = ext4_group_first_block_no(sb, block_group);
+
+ grp_rel_blk = bitmap_blk - grp_first_blk;
+ if (!ext4_test_bit(grp_rel_blk, bh->b_data)) {
+ /* bad block bitmap */
+ brelse(bh);
+ return NULL;
+ }
+
+ /* check whether the inode bitmap block number is set */
+ bitmap_blk = ext4_inode_bitmap(sb, desc);
+ grp_rel_blk = bitmap_blk - grp_first_blk;
+ if (!ext4_test_bit(grp_rel_blk, bh->b_data)) {
+ /* bad block bitmap */
+ brelse(bh);
+ return NULL;
+ }
+ /* check whether the inode table block number is set */
+ bitmap_blk = ext4_inode_table(sb, desc);
+ grp_rel_blk = bitmap_blk - grp_first_blk;
+ if (!ext4_test_bit(grp_rel_blk, bh->b_data)) {
+ /* bad block bitmap */
+ brelse(bh);
+ return NULL;
+ }
+
error_out:
return bh;
}
-
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