linux-kernel - Re: [PATCH] block: nbd: add sanity check for first

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Message-ID: <a04bfff4-bb38-0d21-3432-5086efaa6c69@kernel.dk>
Date:   Mon, 16 Aug 2021 10:56:54 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Skripkin <paskripkin@...il.com>, josef@...icpanda.com
Cc:     hch@....de, linux-block@...r.kernel.org, nbd@...er.debian.org,
        linux-kernel@...r.kernel.org,
        syzbot+9937dc42271cd87d4b98@...kaller.appspotmail.com
Subject: Re: [PATCH] block: nbd: add sanity check for first_minor

On 8/12/21 3:15 AM, Pavel Skripkin wrote:
> Syzbot hit WARNING in internal_create_group(). The problem was in
> too big disk->first_minor.
> 
> disk->first_minor is initialized by value, which comes from userspace
> and there wasn't any sanity checks about value correctness. It can cause
> duplicate creation of sysfs files/links, because disk->first_minor will
> be passed to MKDEV() which causes truncation to byte. Since maximum
> minor value is 0xff, let's check if first_minor is correct minor number.
> 
> NOTE: the root case of the reported warning was in wrong error handling
> in register_disk(), but we can avoid passing knowingly wrong values to
> sysfs API, because sysfs error messages can confuse users. For example:
> user passed 1048576 as index, but sysfs complains about duplicate
> creation of /dev/block/43:0. It's not obvious how 1048576 becomes 0.
> Log and reproducer for above example can be found on syzkaller bug
> report page.

Applied, thanks.

-- 
Jens Axboe