Currently in ext4_valid_block_bitmap() we expect the bitmap to be positioned anywhere between 0 and s_blocksize clusters, but that's wrong because the bitmap can be placed anywhere in the block group. This causes false positives when validating bitmaps on perfectly valid file system layouts. Fix it by checking whether the bitmap is within the group boundary.
The problem can be reproduced using the following
mkfs -t ext3 -E stride=256 /dev/vdb1 mount /dev/vdb1 /mnt/test cd /mnt/test wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.16.3.tar.xz tar xf linux-4.16.3.tar.xz
This will result in the warnings in the logs
EXT4-fs error (device vdb1): ext4_validate_block_bitmap:399: comm tar: bg 84: block 2774529: invalid block bitmap
Signed-off-by: Lukas Czerner lczerner@redhat.com Reported-by: Ilya Dryomov idryomov@gmail.com Fixes: 7dac4a1726a9 ("ext4: add validity checks for bitmap block numbers") Cc: stable@vger.kernel.org --- fs/ext4/balloc.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c index a33d8fb..0c0e383 100644 --- a/fs/ext4/balloc.c +++ b/fs/ext4/balloc.c @@ -338,7 +338,8 @@ static ext4_fsblk_t ext4_valid_block_bitmap(struct super_block *sb, /* check whether block bitmap block number is set */ blk = ext4_block_bitmap(sb, desc); offset = blk - group_first_block; - if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize || + if (offset < 0 || + EXT4_B2C(sbi, offset) >= EXT4_CLUSTERS_PER_GROUP(sb) || !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data)) /* bad block bitmap */ return blk; @@ -346,7 +347,8 @@ static ext4_fsblk_t ext4_valid_block_bitmap(struct super_block *sb, /* check whether the inode bitmap block number is set */ blk = ext4_inode_bitmap(sb, desc); offset = blk - group_first_block; - if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize || + if (offset < 0 || + EXT4_B2C(sbi, offset) >= EXT4_CLUSTERS_PER_GROUP(sb) || !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data)) /* bad block bitmap */ return blk; @@ -354,8 +356,8 @@ static ext4_fsblk_t ext4_valid_block_bitmap(struct super_block *sb, /* check whether the inode table block number is set */ blk = ext4_inode_table(sb, desc); offset = blk - group_first_block; - if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize || - EXT4_B2C(sbi, offset + sbi->s_itb_per_group) >= sb->s_blocksize) + if (offset < 0 || EXT4_B2C(sbi, offset + sbi->s_itb_per_group) >= + EXT4_CLUSTERS_PER_GROUP(sb)) return blk; next_zero_bit = ext4_find_next_zero_bit(bh->b_data, EXT4_B2C(sbi, offset + sbi->s_itb_per_group),