linux-ext4 - Re: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex

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Message-Id: <6A410081-0492-4378-BA66-07AFA7C0DEAF@dilger.ca>
Date:	Wed, 11 Jun 2014 13:01:29 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Akira Fujita <a-fujita@...jp.nec.com>
Cc:	Theodore Tso <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count


On Jun 11, 2014, at 2:38 AM, Akira Fujita <a-fujita@...jp.nec.com> wrote:

> In mke2fs command, if flex_bg count is too large to filesystem blocks count,
> unmountable ext4 which has the out of filesystem block offset is created (Case1).
> Moreover this large flex_bg count causes an unintentional metadata layout
> (bmap-imap-itable-bmap-imap-itable .. in block group) (Case2).
> 
> To fix these issues and keep healthy flex_bg layout, disallow creating ext4
> with obviously large flex_bg count to filesystem blocks count.

Patch looks good to me.
Reviewed-by: Andreas Dilger <adilger@...ger.ca>

This also reminds me of my previous flex_bg patch:
[PATCH][RFC] mke2fs: handle flex_bg collision with backup descriptors
http://permalink.gmane.org/gmane.comp.file-systems.ext4/42298

which fixes the "bmap-imap-itable-bmap-imap-itable" problem when a large
flex_bg size is used.  Sadly, there were no comments on that patch.

Cheers, Andreas

> Steps to reproduce:
> (Case1)
> 1.
> # mke2fs -t ext4 -b 4096 -O ^resize_inode -G $((2**20)) DEV 2130483
> 
> 2.
> # mount -t ext4 DEV MP
> mount: wrong fs type, bad option, bad superblock on /dev/sdb4,
>       missing codepage or helper program, or other error
>       In some cases useful info is found in syslog - try
>       dmesg | tail  or so
> 
> 3.
> # dumpe2fs DEV
> <snip>
> Block count:              2130483
> <snip>
> Flex block group size:    1048576 
> <snip>
> Group 65: (Blocks 2129920-2130482) [INODE_UNINIT]
>  Checksum 0x4cb3, unused inodes 8080
>  Block bitmap at 67 (bg #0 + 67), Inode bitmap at 1048643 (bg #32 + 67)
>  Inode table at 2129979-2130483 (+59)              <---- 2130483 is out of FS!
>  65535 free blocks, 8080 free inodes, 0 directories, 8080 unused inodes
>  Free blocks: 
>  Free inodes: 525201-533280
> 
> (Case2)
> 1.
> # mke2fs -t ext4 -G 2147483648 DEV 3145728
> 
> 2.
> # debugfs -R stats DEV
> <snip>
> Block count:              786432
> <snip>
> Flex block group size:    2147483648
> <snip>
> Group  0: block bitmap at 193, inode bitmap at 194, inode table at 195    <-- 
>           20233 free blocks, 8181 free inodes, 2 used directories, 8181 unused inodes
>           [Checksum 0xa597]
> Group  1: block bitmap at 707, inode bitmap at 708, inode table at 709    <--
>           32575 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
>           [Inode not init, Block not init, Checksum 0x196f]
> Group  2: block bitmap at 1221, inode bitmap at 1222, inode table at 1223 <--
>           32768 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
>           [Inode not init, Block not init, Checksum 0x856f]
> <snip>
> 
> Signed-off-by: Akira Fujita <a-fujita@...jp.nec.com>
> ---
> lib/ext2fs/initialize.c |   24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
> diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c
> index 75fbf8e..34753d0 100644
> --- a/lib/ext2fs/initialize.c
> +++ b/lib/ext2fs/initialize.c
> @@ -91,8 +91,10 @@ errcode_t ext2fs_initialize(const char *name, int flags,
> 	unsigned int	rem;
> 	unsigned int	overhead = 0;
> 	unsigned int	ipg;
> +	unsigned int	flexbg_size;
> 	dgrp_t		i;
> 	blk64_t		free_blocks;
> +	blk64_t		flexbg_overhead;
> 	blk_t		numblocks;
> 	int		rsv_gdt;
> 	int		csum_flag;
> @@ -419,6 +421,28 @@ ipg_retry:
> 	}
> 
> 	/*
> +	 * Calculate the flex_bg related metadata blocks count.
> +	 * It includes the boot block, the super block,
> +	 * the block group descriptors, the reserved gdt blocks,
> +	 * the block bitmaps, the inode bitmaps and the inode tables.
> +	 * This is a simple check, so that the backup superblock and
> +	 * other feature related blocks are not considered.
> +	 */
> +	flexbg_size = 1 << fs->super->s_log_groups_per_flex;
> +	flexbg_overhead = super->s_first_data_block + 1 +
> +		fs->desc_blocks + super->s_reserved_gdt_blocks +
> +		(__u64)flexbg_size * (2 + fs->inode_blocks_per_group);
> +
> +	/*
> +	 * Disallow creating ext4 which breaks flex_bg metadata layout
> +	 * obviously.
> +	 */
> +	if (flexbg_overhead > ext2fs_blocks_count(fs->super)) {
> +		retval = EXT2_ET_INVALID_ARGUMENT;
> +		goto cleanup;
> +	}
> +
> +	/*
> 	 * At this point we know how big the filesystem will be.  So
> 	 * we can do any and all allocations that depend on the block
> 	 * count.
> --
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Cheers, Andreas






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