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ext4: fix crash during online resizing 

When computing maximum size of filesystem possible with given number of
group descriptor blocks, we forget to include s_first_data_block into
the number of blocks. Thus for filesystems with non-zero
s_first_data_block it can happen that computed maximum filesystem size
is actually lower than current filesystem size which confuses the code
and eventually leads to a BUG_ON in ext4_alloc_group_tables() hitting on
flex_gd->count == 0. The problem can be reproduced like:

truncate -s 100g /tmp/image
mkfs.ext4 -b 1024 -E resize=262144 /tmp/image 32768
mount -t ext4 -o loop /tmp/image /mnt
resize2fs /dev/loop0 262145
resize2fs /dev/loop0 300000

Fix the problem by properly including s_first_data_block into the
computed number of filesystem blocks.

Fixes: 1c6bd7173d "ext4: convert file system to meta_bg if needed..."
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
This commit is contained in:
Jan Kara 2019-02-11 13:30:32 -05:00 committed by Theodore Ts'o
parent 6e589291f4
commit f96c3ac8df
1 changed files with 2 additions and 1 deletions
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3
fs/ext4/resize.c
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@ -1960,7 +1960,8 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
le16_to_cpu(es->s_reserved_gdt_blocks);
n_group = n_desc_blocks * EXT4_DESC_PER_BLOCK(sb);
n_blocks_count = (ext4_fsblk_t)n_group *
EXT4_BLOCKS_PER_GROUP(sb);
EXT4_BLOCKS_PER_GROUP(sb) +
le32_to_cpu(es->s_first_data_block);
n_group--; /* set to last group number */
}