linux-ext4 - Re: ext2fs_block_iterate() on fast symlink

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Date:	Thu, 21 Jun 2007 03:33:43 -0600
From:	Andreas Dilger <adilger@...sterfs.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: ext2fs_block_iterate() on fast symlink

On Jun 20, 2007  14:56 +0200, Jan Kara wrote:
>   when  ext2fs_block_iterate() is called on a fast symlink (and I assume
> device inodes would be no different), then random things happen - the
> problem is ext2fs_block_iterate() just blindly takes portions of the inode
> and treats them as block numbers. Now I agree that garbage went in (it
> makes no sence to call this function on such inode) so garbage results but
> maybe it would be nicer to handle it more gracefully. Attached patch should
> do it.

> --- a/lib/ext2fs/inode.c	2007-06-20 13:55:52.000000000 +0200
> +++ b/lib/ext2fs/inode.c	2007-06-20 14:11:15.000000000 +0200
> @@ -771,6 +771,10 @@ errcode_t ext2fs_get_blocks(ext2_filsys 
>  	retval = ext2fs_read_inode(fs, ino, &inode);
>  	if (retval)
>  		return retval;
> +	if (LINUX_S_ISCHR(inode.i_mode) || LINUX_S_ISBLK(inode.i_mode) ||
> +	    (LINUX_S_ISLNK(inode.i_mode) &&
> +	     ext2fs_inode_data_blocks(fs, &inode) == 0))
> +		return EXT2_ET_INVAL_INODE_TYPE;

I would prefer that we NOT continue to make fast symlinks conditional upon
the i_blocks count.  That causes problems if e.g. an EA block is present
(that would cause this blocks == 0 test to incorrectly fail), and may making
the check (blocks - !!i_file_acl) can still fail for other reasons where a
block is added to an inode (e.g. if we have larger EAs, etc).

I'd prefer to make this check "i_size < sizeof(i_block)" or similar, which
has always been true for fast symlinks, for every kernel that I have ever
seen.


Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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