linux-ext4 - Re: [PATCH] libext2fs: write only core inode in update

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Date:	Wed, 17 Jun 2009 11:35:37 -0400
From:	Theodore Tso <tytso@....edu>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] libext2fs: write only core inode in update_path()

On Tue, Jun 16, 2009 at 07:57:59PM -0500, Eric Sandeen wrote:
> libext2fs: write only core inode in update_path()
> 
> The ext2_extent_handle only has a struct ext2_inode allocated on
> it, and the same amount copied into it in that same function, 
> but in update_path() we're possibly writing out more than that - 
> for example 256 bytes, from that address.  This causes uninitialized 
> memory to get  written to disk, overwriting the parts of the 
> inode past the osd2 member (the end of the smaller structure).

Oh, I see.  The bug was introduced by commit 84b239ae 


    libext2fs: add ext2fs_extent_open2
    
    The patch below adds a function, ext2fs_extent_open2(), that behaves
    as ext2fs_extent_open(), but will use the user-supplied inode
    structure when opening an extent instead of reading the inode from
    disk.  It also changes several of the calls to extent_open() to use
    this enhancement.
    
    Signed-off-by: Nic Case <number9652@...oo.com>
    Signed-off-by: "Theodore Ts'o" <tytso@....edu>

Which replaced ext2fs_read_inode_full with ext2fs_read_inode(); which
is fine, extents.c doesn't need to use the full inode; but it didn't
change ext2fs_write_inode_full() with ext2fs_write_inode().

> diff --git a/lib/ext2fs/extent.c b/lib/ext2fs/extent.c
> index b7eb617..0dfee62 100644
> --- a/lib/ext2fs/extent.c
> +++ b/lib/ext2fs/extent.c
> @@ -547,7 +547,7 @@ static errcode_t update_path(ext2_extent_handle_t handle)
>  
>  	if (handle->level == 0) {
>  		retval = ext2fs_write_inode_full(handle->fs, handle->ino,
> -			   handle->inode, EXT2_INODE_SIZE(handle->fs->super));
> +			   handle->inode, sizeof(struct ext2_inode));

Probably it would be better/simpler to replace this with:

		retval = ext2fs_write_inode(handle->fs, handle->ino,
					    handle->inode);

							- Ted
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