linux-kernel - Re: [PATCH] udf: Don't corrupt unalloc spacetable when writing it

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Date:	Thu, 9 Jul 2015 17:16:03 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Steven J. Magnani" <steve.magnani@...idescorp.com>
Cc:	jack@...e.cz, linux-kernel@...r.kernel.org,
	"Steven J. Magnani" <steve@...idescorp.com>
Subject: Re: [PATCH] udf: Don't corrupt unalloc spacetable when writing it

On Tue 07-07-15 13:06:05, Steven J. Magnani wrote:
> For a UDF filesystem configured with an Unallocated Space Table,
> a filesystem operation that triggers an update to the table results
> in on-disk corruption that prevents remounting:
> 
>   udf_read_tagged: tag version 0x0000 != 0x0002 || 0x0003, block 274
> 
> For example:
>   1. Create a filesystem
>       $ mkudffs --media-type=hd --blocksize=512 --lvid=BUGTEST \
>               --vid=BUGTEST --fsid=BUGTEST --space=unalloctable \
>               /dev/mmcblk0
> 
>   2. Mount it
>       # mount /dev/mmcblk0 /mnt
> 
>   3. Create a file
>       $ echo "No corruption, please" > /mnt/new.file
> 
>   4. Umount
>       # umount /mnt
> 
>   5. Attempt remount
>       # mount /dev/mmcblk0 /mnt
> 
> This appears to be a longstanding bug caused by zero-initialization of
> the Unallocated Space Entry block buffer and only partial repopulation
> of required fields before writing to disk. 
> 
> Commit 0adfb339fd64 ("udf: Fix unalloc space handling in udf_update_inode")
> addressed one such field, but several others are required.
> 
> Signed-off-by: Steven J. Magnani <steve@...idescorp.com>

So the patch looks good to me. But what kind of mkudffs are you using?
Because when I use the command you wrote into the changelog, I cannot mount
the filesystem. The kernel complains about:

UDF-fs: error (device ubdb): udf_read_inode: (ino 274) failed ident=256
mount: /dev/ubdb: can't read superblock

Now ident 256 is TAG_IDENT_FSD (file set descriptor). So apparently my
mkudffs doesn't create proper partition table with your parameters...

								Honza

> ---
> diff -uprN a/fs/udf/inode.c b/fs/udf/inode.c
> --- a/fs/udf/inode.c	2015-07-06 13:42:08.861499890 -0500
> +++ b/fs/udf/inode.c	2015-07-06 13:42:18.153499469 -0500
> @@ -1652,17 +1652,9 @@ static int udf_update_inode(struct inode
>  		       iinfo->i_ext.i_data, inode->i_sb->s_blocksize -
>  					sizeof(struct unallocSpaceEntry));
>  		use->descTag.tagIdent = cpu_to_le16(TAG_IDENT_USE);
> -		use->descTag.tagLocation =
> -				cpu_to_le32(iinfo->i_location.logicalBlockNum);
> -		crclen = sizeof(struct unallocSpaceEntry) +
> -				iinfo->i_lenAlloc - sizeof(struct tag);
> -		use->descTag.descCRCLength = cpu_to_le16(crclen);
> -		use->descTag.descCRC = cpu_to_le16(crc_itu_t(0, (char *)use +
> -							   sizeof(struct tag),
> -							   crclen));
> -		use->descTag.tagChecksum = udf_tag_checksum(&use->descTag);
> +		crclen = sizeof(struct unallocSpaceEntry);
>  
> -		goto out;
> +		goto finish;
>  	}
>  
>  	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_UID_FORGET))
> @@ -1782,6 +1774,8 @@ static int udf_update_inode(struct inode
>  		efe->descTag.tagIdent = cpu_to_le16(TAG_IDENT_EFE);
>  		crclen = sizeof(struct extendedFileEntry);
>  	}
> +
> +finish:
>  	if (iinfo->i_strat4096) {
>  		fe->icbTag.strategyType = cpu_to_le16(4096);
>  		fe->icbTag.strategyParameter = cpu_to_le16(1);
> @@ -1791,7 +1785,9 @@ static int udf_update_inode(struct inode
>  		fe->icbTag.numEntries = cpu_to_le16(1);
>  	}
>  
> -	if (S_ISDIR(inode->i_mode))
> +	if (iinfo->i_use)
> +		fe->icbTag.fileType = ICBTAG_FILE_TYPE_USE;
> +	else if (S_ISDIR(inode->i_mode))
>  		fe->icbTag.fileType = ICBTAG_FILE_TYPE_DIRECTORY;
>  	else if (S_ISREG(inode->i_mode))
>  		fe->icbTag.fileType = ICBTAG_FILE_TYPE_REGULAR;
> @@ -1828,7 +1824,6 @@ static int udf_update_inode(struct inode
>  						  crclen));
>  	fe->descTag.tagChecksum = udf_tag_checksum(&fe->descTag);
>  
> -out:
>  	set_buffer_uptodate(bh);
>  	unlock_buffer(bh);
>  
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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