linux-ext4 - Re: [PATCH 2/2] ext2fs: Fix off-by-one in dx_grow

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Date:   Mon, 30 Mar 2020 16:55:31 +0200
From:   Jan Kara <jack@...e.cz>
To:     Lukas Czerner <lczerner@...hat.com>
Cc:     Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2] ext2fs: Fix off-by-one in dx_grow_tree()

On Mon 30-03-20 15:27:12, Lukas Czerner wrote:
> On Mon, Mar 30, 2020 at 11:09:32AM +0200, Jan Kara wrote:
> > There is an off-by-one error in dx_grow_tree() when checking whether we
> > can add another level to the tree. Thus we can grow tree too much
> > leading to possible crashes in the library or corrupted filesystem. Fix
> > the bug.
> 
> Looks good, thanks
> 
> Reviewed-by: Lukas Czerner <lczerner@...hat.com>
> 
> Don't we have basically the same off-by-one in
> e2fsck/pass1.c handle_htree() ?
> 
>        if ((root->indirect_levels > ext2_dir_htree_level(fs)) &&
>            fix_problem(ctx, PR_1_HTREE_DEPTH, pctx))

I don't think so. It is indeed correct for root->indirect_levels to be
equal to ext2_dir_htree_level(). However dx_grow_tree() is going to
increase root->indirect_levels by 1 which is where tree would become
invalid...

								Honza

> > 
> > Signed-off-by: Jan Kara <jack@...e.cz>
> > ---
> >  lib/ext2fs/link.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/lib/ext2fs/link.c b/lib/ext2fs/link.c
> > index 7b5bb022117c..469eea8cd06d 100644
> > --- a/lib/ext2fs/link.c
> > +++ b/lib/ext2fs/link.c
> > @@ -473,7 +473,7 @@ static errcode_t dx_grow_tree(ext2_filsys fs, ext2_ino_t dir,
> >  		    ext2fs_le16_to_cpu(info->frames[i].head->limit))
> >  			break;
> >  	/* Need to grow tree depth? */
> > -	if (i < 0 && info->levels > ext2_dir_htree_level(fs))
> > +	if (i < 0 && info->levels >= ext2_dir_htree_level(fs))
> >  		return EXT2_ET_DIR_NO_SPACE;
> >  	lblk = size / fs->blocksize;
> >  	size += fs->blocksize;
> > -- 
> > 2.16.4
> > 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR