linux-kernel - Re: [PATCH] staging: rtl8192u: fix a null pointer dereference on a null dev pointer

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Message-ID: <8bad22a0-5ddc-2ab3-6319-77dcf96e3be6@canonical.com>
Date:   Mon, 4 Feb 2019 14:15:23 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        John Whitmore <johnfwhitmore@...il.com>,
        devel@...verdev.osuosl.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: rtl8192u: fix a null pointer dereference on a
 null dev pointer

On 03/02/2019 11:31, Dan Carpenter wrote:
> On Sat, Feb 02, 2019 at 10:56:27PM +0000, Colin King wrote:
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> There is an earlier null check on pointer dev which implies it may be null,
>> however the assignment of pointer pref and the call to free_ieee82011 on
>> a null dev can cause null pointer dereference errors.  Fix this by moving
>> the assignment of priv and the the call to free_ieee80211 into the block of
>> code that performs the null dev sanity check.
>>
>> Detected by CoverityScan, CID#143078 ("Dereference after null check")
>>
>> Fixes: 8fc8598e61f6 ("Staging: Added Realtek rtl8192u driver to staging")
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>  drivers/staging/rtl8192u/r8192U_core.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/rtl8192u/r8192U_core.c b/drivers/staging/rtl8192u/r8192U_core.c
>> index 0ac0bbf7d923..4741a29326ea 100644
>> --- a/drivers/staging/rtl8192u/r8192U_core.c
>> +++ b/drivers/staging/rtl8192u/r8192U_core.c
>> @@ -4955,9 +4955,10 @@ static void rtl8192_cancel_deferred_work(struct r8192_priv *priv)
>>  static void rtl8192_usb_disconnect(struct usb_interface *intf)
>>  {
>>  	struct net_device *dev = usb_get_intfdata(intf);
>> -	struct r8192_priv *priv = ieee80211_priv(dev);
>>  
>>  	if (dev) {
>> +		struct r8192_priv *priv = ieee80211_priv(dev);
> 
> "dev" can't actually be NULL.  Look how we call usb_set_intfdata() in
> probe().  It's better to remove the check instead.

Yep, good point. I'll send a V2.

> 
> regards,
> dan carpenter
>