[PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count

[PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count

[Akira Fujita]

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.

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@rs.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.

Re: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count

[Andreas Dilger]

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On Jun 11, 2014, at 2:38 AM, Akira Fujita <a-fujita@rs.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@dilger.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@rs.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.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


Cheers, Andreas






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Re: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count

[Darrick J. Wong]

On Wed, Jun 11, 2014 at 01:01:29PM -0600, Andreas Dilger wrote:
> 
> On Jun 11, 2014, at 2:38 AM, Akira Fujita <a-fujita@rs.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@dilger.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.

I had wondered if you were planning to address the FIXMEs in the patch, but
then forgot to ever follow up... :/

--D

> 
> 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@rs.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.
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> 
> Cheers, Andreas
> 
> 
> 
> 
> 

Re: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count

[Andreas Dilger]

[-- Attachment #1: Type: text/plain, Size: 1125 bytes --]

On Jun 12, 2014, at 5:50 PM, Darrick J. Wong <darrick.wong@oracle.com> wrote:
> On Wed, Jun 11, 2014 at 01:01:29PM -0600, Andreas Dilger wrote:
>> 
>> 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.
> 
> I had wondered if you were planning to address the FIXMEs in the patch, but
> then forgot to ever follow up... :/

Well, I was thinking that the patch was good enough to land as-is.  It fixes 99% the problem for flex_bg size up to 65536, but only 95% of the groups for flex_bg of 131072.  I guess I'll send it out again without [RFC], and if people start using flex_bg >= 131072 (which is enough for all the metadata in a 16TB chunk) then we can work out the final details.  I suspect that the sparse_super2 feature would probably become more prevalent and avoid this problem entirely.

Cheers, Andreas






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Re: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count

[Theodore Ts'o]

On Wed, Jun 11, 2014 at 08:38:10AM +0000, Akira Fujita 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.

Applied, thanks.

							- Ted