linux-kernel - Re: [PATCH 13/25] ubifs: authentication: Add hashes to index nodes

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Date:   Fri, 7 Sep 2018 12:25:16 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Richard Weinberger <richard@....at>
Cc:     linux-mtd@...ts.infradead.org, David Gstir <david@...ma-star.at>,
        kernel@...gutronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/25] ubifs: authentication: Add hashes to index nodes

On Mon, Aug 27, 2018 at 09:36:56PM +0200, Richard Weinberger wrote:
> > diff --git a/fs/ubifs/tnc.c b/fs/ubifs/tnc.c
> > index a47fced47823..a00809d4fe6f 100644
> > --- a/fs/ubifs/tnc.c
> > +++ b/fs/ubifs/tnc.c
> > @@ -488,6 +488,12 @@ static int try_read_node(const struct ubifs_info *c, void *buf, int type,
> >  	if (crc != node_crc)
> >  		return 0;
> >  
> > +	err = ubifs_node_check_hash(c, buf, zbr->hash);
> > +	if (err) {
> > +		ubifs_err(c, "hash mismatch on node at LEB %d:%d", lnum, offs);
> > +		return 0;
> > +	}
> 
> Hmm, I think a global "hash is bad" handler would be nice to have.
> That way we always report in the same way.

I created a function reporting a bad hash, so every failure goes through
the same code...

> 
> Maybe also a new file system specific ioctl to query whether a hash
> failure was noticed.

but I'll leave that for a later excercise if that's ok. I am unsure how
useful such an ioctl() is. It's too easy to interpret such a hash
mismatch as some kind of security violation when it's more likely just a
bug somewhere.

> > @@ -868,6 +877,23 @@ static int write_index(struct ubifs_info *c)
> >  		}
> >  		len = ubifs_idx_node_sz(c, znode->child_cnt);
> >  		ubifs_prepare_node(c, idx, len, 0);
> > +		ubifs_node_calc_hash(c, idx, hash);
> > +
> > +		mutex_lock(&c->tnc_mutex);
> 
> This lock looks correct too me.
> Just in case, you did test with lockdep enabled? :-)

Yes, I had lockdep enabled in all my tests.

Sascha

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