linux-ext4 - Re: [PATCH] ext4: catch integer overflow in ext4_cache

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Message-ID: <20200715115312.GL23073@quack2.suse.cz>
Date:   Wed, 15 Jul 2020 13:53:12 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
        linux-ext4@...r.kernel.org,
        Wolfgang Frisch <wolfgang.frisch@...e.com>
Subject: Re: [PATCH] ext4: catch integer overflow in ext4_cache_extents

On Tue 14-07-20 14:31:22, Jan Kara wrote:
> On Mon 13-07-20 19:14:47, Ritesh Harjani wrote:
> > 
> > 
> > On 7/13/20 6:28 PM, Jan Kara wrote:
> > > From: Wolfgang Frisch <wolfgang.frisch@...e.com>
> > > 
> > > When extent tree is corrupted we can hit BUG_ON in
> > > ext4_es_cache_extent(). Check for this and abort caching instead of
> > > crashing the machine.
> > 
> > Was it intentionally made corrupted by crafting a corrupted disk image?
> 
> I'm not sure how Wolfgang hit the issue. I'd expect some fs image
> fuzzing... Wolfgang?
> 
> > Are there more such logic in place which checks for such corruption at other
> > places?
> 
> That's a good question. But now that I'm looking at it ext4_ext_check()
> should actually catch a corruption like this. It is only the path in
> ext4_find_extent()->ext4_cache_extents() that can face the issue so
> probably instead of a fix in ext4_cache_extents() we should rather add more
> careful extent info checks for the extents contained directly in the inode.
> I'll look into it.

I was checking this more and indeed the problem can actually happen only
with the journal inode because that is special-cased when checking extent
tree. I'll send a new series that fixes this in a cleaner way.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR