linux-kernel - Re: [PATCH] net: usbnet: Fix potential NULL pointer dereference

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Message-ID: <20231101125511.222629-1-renmingshuai@huawei.com>
Date:   Wed, 1 Nov 2023 20:55:11 +0800
From:   Ren Mingshuai <renmingshuai@...wei.com>
To:     <renmingshuai@...wei.com>
CC:     <caowangbao@...wei.com>, <davem@...emloft.net>,
        <khlebnikov@...nvz.org>, <liaichun@...wei.com>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <oneukum@...e.com>, <yanan@...wei.com>
Subject: Re: [PATCH] net: usbnet: Fix potential NULL pointer dereference

>23ba07991dad said SKB can be NULL without describing the triggering
>scenario. Always Check it before dereference to void potential NULL
>pointer dereference.
I've tried to find out the scenarios where SKB is NULL, but failed.
It seems impossible for SKB to be NULL. If SKB can be NULL, please tell
me the reason and I'd be very grateful.

>Fix smatch warning:
>drivers/net/usb/usbnet.c:1380 usbnet_start_xmit() error: we previously assumed 'skb' could be null (see line 1359)
>
>Signed-off-by: Ren Mingshuai <renmingshuai@...wei.com>
>---
> drivers/net/usb/usbnet.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
>diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
>index 64a9a80b2309..386cb1a4ff03 100644
>--- a/drivers/net/usb/usbnet.c
>+++ b/drivers/net/usb/usbnet.c
>@@ -1374,6 +1374,11 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
>                }
>        }
>
>+       if (!skb) {
>+               netif_dbg(dev, tx_err, dev->net, "tx skb is NULL\n");
>+               goto drop;
>+       }
>+
>        if (!(urb = usb_alloc_urb (0, GFP_ATOMIC))) {
>                netif_dbg(dev, tx_err, dev->net, "no urb\n");
>                goto drop;
>--
>2.33.0