linux-kernel - Re: [RFC PATCH] mm: truncate: flush lru cache for evicted inode

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Date: Fri, 14 Jun 2024 14:42:20 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Hillf Danton <hdanton@...a.com>
Cc: linux-mm@...ck.org, Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	syzbot+d79afb004be235636ee8@...kaller.appspotmail.com
Subject: Re: [RFC PATCH] mm: truncate: flush lru cache for evicted inode

On Fri, Jun 14, 2024 at 09:18:56PM +0800, Hillf Danton wrote:
> Flush lru cache to avoid folio->mapping uaf in case of inode teardown.

What?  inodes are supposed to have all their folios removed before
being freed.  Part of removing a folio sets the folio->mapping to NULL.
Where is the report?

> Reported-and-tested-by: syzbot+d79afb004be235636ee8@...kaller.appspotmail.com
> Signed-off-by: Hillf Danton <hdanton@...a.com>
> ---
> Post for comments because lru_add_drain_all() is too haevy a hammer.
> 
> --- x/mm/truncate.c
> +++ y/mm/truncate.c
> @@ -419,6 +419,9 @@ void truncate_inode_pages_range(struct a
>  		truncate_folio_batch_exceptionals(mapping, &fbatch, indices);
>  		folio_batch_release(&fbatch);
>  	}
> +
> +	if (mapping_exiting(mapping))
> +		lru_add_drain_all();
>  }
>  EXPORT_SYMBOL(truncate_inode_pages_range);
>  
> --