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Subject[PATCH 5.0 123/238] ext4: fix crash during online resizing
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@suse.cz>

commit f96c3ac8dfc24b4e38fc4c2eba5fea2107b929d1 upstream.

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: 1c6bd7173d66 "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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext4/resize.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1960,7 +1960,8 @@ retry:
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 */
}


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