linux-ext4 - Re: [RFC PATCH v2 7/7] ext4: fix race between blkdev_releasepage() and ext4_put

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Date:   Thu, 15 Apr 2021 15:52:35 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        tytso@....edu, adilger.kernel@...ger.ca, jack@...e.cz,
        yukuai3@...wei.com
Subject: Re: [RFC PATCH v2 7/7] ext4: fix race between blkdev_releasepage()
 and ext4_put_super()

On Wed, Apr 14, 2021 at 09:47:37PM +0800, Zhang Yi wrote:
> There still exist a use after free issue when accessing the journal
> structure and ext4_sb_info structure on freeing bdev buffers in
> bdev_try_to_free_page(). The problem is bdev_try_to_free_page() could be
> raced by ext4_put_super(), it dose freeing sb->s_fs_info and
> sbi->s_journal while release page progress are still accessing them.
> So it could end up trigger use-after-free or NULL pointer dereference.

I think the right fix is to not even call into ->bdev_try_to_free_page
unless the superblock is active.