Re: [PATCH] bcachefs: Fix NULL ptr dereference in btree_node_iter_and_journal_peek

[Kent Overstreet]

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@xxxxxxxxx> 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.