linux-kernel - Re: [PATCH] mm: folio-compat: fix bug for pagecache_get

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Message-Id: <20221018134834.97e685f9a9445c4553ce158b@linux-foundation.org>
Date:   Tue, 18 Oct 2022 13:48:34 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Tuo Cao <91tuocao@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: folio-compat: fix bug for pagecache_get_page

On Tue, 18 Oct 2022 15:39:39 +0100 Matthew Wilcox <willy@...radead.org> wrote:

> On Tue, Oct 18, 2022 at 10:36:39PM +0800, Tuo Cao wrote:
> > The folio returned from __filemap_get_folio may be a NULL, it will
> > causes the kernel crash when access folio->page.
> 
> This is not a bug.  &folio->page does not dereference folio but performs
> pointer arithmetic.

This is the third attempt to "fix" this.  So far.  I think we should
take the hint and make the check for a null pointer more explicit.