linux-kernel - Re: drivers/char: suspected null-pointer dereference problem in handle_control

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Date:   Tue, 26 Oct 2021 12:29:31 +0200
From:   Amit Shah <amit@...radead.org>
To:     YE Chengfeng <cyeaa@...nect.ust.hk>,
        "amit@...nel.org" <amit@...nel.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: drivers/char: suspected null-pointer dereference problem in
 handle_control_message

On Tue, 2021-10-26 at 06:17 +0000, YE Chengfeng wrote:
> Hi,
>  
> https://github.com/torvalds/linux/blob/master/drivers/char/virtio_console.c#L1657
>  
> Our experimental static analysis tool detects a suspected null-pointer-dereference problem. We manually check it, but It still could be false positive because we are not familiar with the code. We report this to you just in case.
>  
> We notice that in some branches of switch case at line #1582, the pointer port is null check. But null check is missing at line #1657 and line #1633. It seems like a suspected null-pointer dereference pointer. Would you like to spare some time to have a look at it?

For this NULL deref to happen, the host will have to send a port_name
command before a port_add command.  Worrying about that isn't
worthwhile.  If you'd like to add a generic `if (unlikely(!port))`
after line 1579 there, that'd be fine as a hint to the static analysis
tools, though, so just for that reason, it might be worthwhile.

		Amit