linux-kernel - Re: [Devel] [PATCH] incorrect error handling inside generic_file_direct_write

Open Source and information security mailing list archives

Date:	Mon, 11 Dec 2006 15:38:07 +0300
From:	Kirill Korotaev <dev@...ru>
To:	Andrew Morton <akpm@...l.org>
CC:	linux-kernel@...r.kernel.org,
	Linux Memory Management <linux-mm@...ck.org>,
	devel@...nvz.org, Monakhov Dmintiy <dmonakhov@...ru>
Subject: Re: [Devel] [PATCH] incorrect error handling inside	generic_file_direct_write

I guess you forgot to add Andrew on CC.

Thanks,
Kirill

> OpenVZ team has discovered error inside generic_file_direct_write()
> If generic_file_direct_IO() has fail (ENOSPC condition) it may have instantiated
> a few blocks outside i_size. And fsck will complain about wrong i_size
> (ext2, ext3 and reiserfs interpret i_size and biggest block difference as error),
> after fsck will fix error i_size will be increased to the biggest block,
> but this blocks contain gurbage from previous write attempt, this is not 
> information leak, but its silence file data corruption. 
> We need truncate any block beyond i_size after write have failed , do in simular
> generic_file_buffered_write() error path.
> 
> Exampe:
> open("mnt2/FILE3", O_WRONLY|O_CREAT|O_DIRECT, 0666) = 3
> write(3, "aaaaaa"..., 4096) = -1 ENOSPC (No space left on device)
> 
> stat mnt2/FILE3
> File: `mnt2/FILE3'
> Size: 0               Blocks: 4          IO Block: 4096   regular empty file
> 
>>>>>>>>>>>>>>>>>>>>>>>^^^^^^^^^^ file size is less than biggest block idx
> 
> Device: 700h/1792d      Inode: 14          Links: 1
> Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
> 
> fsck.ext2 -f -n  mnt1/fs_img
> Pass 1: Checking inodes, blocks, and sizes
> Inode 14, i_size is 0, should be 2048.  Fix? no
> 
> Signed-off-by: Dmitriy Monakhov <dmonakhov@...nvz.org>
> ----------
> 
> 
> ------------------------------------------------------------------------
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 7b84dc8..bf7cf6c 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2041,6 +2041,14 @@ generic_file_direct_write(struct kiocb *
>  			mark_inode_dirty(inode);
>  		}
>  		*ppos = end;
> +	} else if (written < 0) {
> +		loff_t isize = i_size_read(inode);
> +		/*
> +		 * generic_file_direct_IO() may have instantiated a few blocks
> +		 * outside i_size.  Trim these off again.
> +		 */
> +		if (pos + count > isize)
> +			vmtruncate(inode, isize);
>  	}
>  
>  	/*
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Devel mailing list
> Devel@...nvz.org
> https://openvz.org/mailman/listinfo/devel

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