linux-ext4 - Re: [PATCH] ext4: Fix ext4_empty_dir() for directories with holes

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Message-ID: <20191127195312.GB22921@mit.edu>
Date:   Wed, 27 Nov 2019 14:53:12 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix ext4_empty_dir() for directories with holes

On Wed, Nov 27, 2019 at 02:44:15PM -0500, Theodore Y. Ts'o wrote:
> On Wed, Nov 27, 2019 at 02:12:58PM +0100, Jan Kara wrote:
> > Function ext4_empty_dir() doesn't correctly handle directories with
> > holes and crashes on bh->b_data dereference when bh is NULL....
> 
> Hi Jan,
> 
> Thanks for the patch.
> 
> However, it looks like we're still vulnerable to the first block of
> the directory being NULL?
> 
> > @@ -2833,19 +2833,25 @@ bool ext4_empty_dir(struct inode *inode)
> >  		return true;
> >  
> >  	de = (struct ext4_dir_entry_2 *) bh->b_data;
>                                          ^^^^^^^^^^^

Ah, never mind.  Since we're calling ext4_read_dirblock() with
DIRENT_HTREE, if bh is NULL, it will get caught earlier, and
ext4_read_dirblock() will return ERR_PTR(-EFSCORRUPTED).

						- Ted