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From:   Ren Mingshuai <renmingshuai@huawei.com>
To:     <gregkh@linuxfoundation.org>
CC:     <caowangbao@huawei.com>, <davem@davemloft.net>,
        <edumazet@google.com>, <jirislaby@kernel.org>, <kuba@kernel.org>,
        <liaichun@huawei.com>, <linux-kernel@vger.kernel.org>,
        <linux-usb@vger.kernel.org>, <renmingshuai@huawei.com>,
        <yanan@huawei.com>
Subject: Re: [PATCH] tty: hso: Fix potential null pointer dereference.
Date:   Thu, 2 Nov 2023 10:09:08 +0800
Message-ID: <20231102020908.692325-1-renmingshuai@huawei.com>
In-Reply-To: <2023110139-spearmint-throttle-ed90@gregkh>
References: <2023110139-spearmint-throttle-ed90@gregkh>
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>> Generally, the old always points to the address of a ktermios structure,
>> so old is unlikely to be NULL. Still check it before dereference as
>> elsewhere.
>
>If it can not happen, there is no need to check it.  So unless you can
>prove that this ever could happen, this change isn't needed, right?
>
>thanks,
>
>greg k-h
Thanks for reply. I agree with you. The reason for checking old there
is that it is checked at the beginning in hso_serial_set_termios(). It is
better to check it both or not, right?
Delete it to avoid smatch complaints.
drivers/net/usb/hso.c:1399 hso_serial_set_termios() error: we previously assumed 'old' could be null (see line 1389).

diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
index 4ad829ab54d3..383ff8b04473 100644
--- a/drivers/net/usb/hso.c
+++ b/drivers/net/usb/hso.c
@@ -1386,10 +1386,9 @@ static void hso_serial_set_termios(struct tty_struct *tty,
        struct hso_serial *serial = tty->driver_data;
        unsigned long flags;

-       if (old)
-               hso_dbg(0x16, "Termios called with: cflags new[%u] - old[%u]\n",
-                       (unsigned int)tty->termios.c_cflag,
-                       (unsigned int)old->c_cflag);
+       hso_dbg(0x16, "Termios called with: cflags new[%u] - old[%u]\n",
+               (unsigned int)tty->termios.c_cflag,
+               (unsigned int)old->c_cflag);

        /* the actual setup */
        spin_lock_irqsave(&serial->serial_lock, flags);