linux-kernel - Re: [PATCH] bcachefs: Fix NULL ptr dereference in btree_node_iter_and_journal

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Message-ID: <bYeu9DQqsfsNY3FFRdkXqypW-RCyXXx63_QipilBHZIJDJluqBfaaSpO4YkudfinbGDsq91vJFmvQOge3BFGL5AkUqswR4eIpGwbwz41fIM=@proton.me>
Date: Sat, 26 Oct 2024 00:23:40 +0000
From: Piotr Zalewski <pZ010001011111@...ton.me>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Alan Huang <mmpgouride@...il.com>, linux-bcachefs@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, skhan@...uxfoundation.org, syzbot+005ef9aa519f30d97657@...kaller.appspotmail.com
Subject: Re: [PATCH] bcachefs: Fix NULL ptr dereference in btree_node_iter_and_journal_peek






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On Saturday, October 26th, 2024 at 2:16 AM, Kent Overstreet <kent.overstreet@...ux.dev> wrote:

> On Fri, Oct 25, 2024 at 08:11:50PM -0400, Kent Overstreet wrote:
> 
> > On Wed, Oct 23, 2024 at 03:33:22PM +0800, Alan Huang wrote:
> > 
> > > On Oct 23, 2024, at 15:21, Piotr Zalewski pZ010001011111@...ton.me wrote:
> > > 
> > > > Add NULL check for key returned from bch2_btree_and_journal_iter_peek in
> > > > btree_node_iter_and_journal_peek to avoid NULL ptr dereference in
> > > > bch2_bkey_buf_reassemble.
> > > 
> > > It would be helpful if the commit message explained why k.k is null in this case
> > 
> > This code is only for iterating over interior btree nodes - k.k is only
> > null when we have a bad btree topology (gaps).
> > 
> > Piotr, could you add a comment to that effect?
> 
> 
> Actually, not just that - when this happens we should flag the
> filesystem as having topology repairs, and possibly start topology
> repair.
> 
> Calling bch2_topology_error() will do that.
> 
> We definitely want to log an error message, too; it should reference the
> btree node we're iterating over and explain that it's missing child
> nodes.

Thanks for the clarification. I will send v2 tomorrow :)