ACK: [x/azure,c/azure][PATCH] ext4: fix crash during online resizing

[Tyler Hicks]

On 2019-07-04 15:16:45, Marcelo Henrique Cerri wrote:
> From: Jan Kara <jack at suse.cz>
> 
> BugLink: http://bugs.launchpad.net/bugs/1835322
> 
> 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 at suse.cz>
> Signed-off-by: Theodore Ts'o <tytso at mit.edu>
> Cc: stable at vger.kernel.org
> (cherry picked from commit f96c3ac8dfc24b4e38fc4c2eba5fea2107b929d1)
> Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>

Acked-by: Tyler Hicks <tyhicks at canonical.com>

Tyler

> ---
>  fs/ext4/resize.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> index c38f9e838aef..b7809d16a5d4 100644
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -1957,7 +1957,8 @@ 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 */
>  		}
>  
> -- 
> 2.20.1
> 
> 
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