linux-ext4 - Re: [PATCH] ext4: Fix crash during online resizing

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Message-ID: <20190211184335.GN23000@mit.edu>
Date:   Mon, 11 Feb 2019 13:43:35 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
CC:     <linux-ext4@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH] ext4: Fix crash during online resizing

On Thu, Jan 24, 2019 at 05:26:06PM +0100, Jan Kara wrote:
> 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.
> 
> CC: stable@...r.kernel.org
> Fixes: 1c6bd7173d66 "ext4: convert file system to meta_bg if needed..."
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, applied.

					- Ted