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Date:   Mon, 16 Nov 2020 16:38:33 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc:     David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org,
        Anand Jain <anand.jain@oracle.com>,
        Nikolay Borisov <nborisov@suse.com>,
        syzbot+582e66e5edf36a22c7b0@syzkaller.appspotmail.com
Subject: Re: [PATCH v2] btrfs: don't access possibly stale fs_info data for
 printing duplicate device
Message-ID: <20201116153833.GO6756@twin.jikos.cz>
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        Johannes Thumshirn <johannes.thumshirn@wdc.com>,
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        Anand Jain <anand.jain@oracle.com>,
        Nikolay Borisov <nborisov@suse.com>,
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References: <0e9eb675e0a199bf034f13c58fbe5678f4e94a3c.1605513154.git.johannes.thumshirn@wdc.com>
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On Mon, Nov 16, 2020 at 04:52:54PM +0900, Johannes Thumshirn wrote:
> Syzbot reported a possible use-after-free when printing a duplicate device
> warning device_list_add().
> 
> At this point it can happen that a btrfs_device::fs_info is not correctly
> setup yet, so we're accessing stale data, when printing the warning
> message using the btrfs_printk() wrappers.
> 
> Instead of printing possibly uninitialized or already freed memory in
> btrfs_printk(), explicitly pass in a NULL fs_info so the printing of the
> device name will be skipped altogether.

This would be good to add some info about the evolution of the fix, also
a comment saying why we can't use fs_info.