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

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Message-ID: <20070621095449.GA3744@duck.suse.cz>
Date:	Thu, 21 Jun 2007 11:54:49 +0200
From:	Jan Kara <jack@...e.cz>
To:	Andreas Dilger <adilger@...sterfs.com>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: ext2fs_block_iterate() on fast symlink

On Thu 21-06-07 03:33:43, Andreas Dilger wrote:
> 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).
  Note that ext2fs_inode_data_blocks() subtract number of EA blocks, so it
is equivalent to (blocks - !!i_file_acl). The function is supposed to
return the number of real data blocks so the test should be fine even in
future.

> 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.
  Personally I don't mind much. If Ted finds this better, I'll change that.
Maybe introducing some macro LINUX_S_ISFASTLNK() would be fine.

									Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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