linux-kernel - Re: [PATCH] staging: gpib: Move free after the variable use has been completed

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Message-ID: <748e78b9-3c70-4300-9de4-6df00dffe4c3@linuxfoundation.org>
Date: Tue, 15 Oct 2024 17:29:20 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: "Everest K.C." <everestkc@...restkc.com.np>
Cc: dpenkler@...il.com, gregkh@...uxfoundation.org,
 linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] staging: gpib: Move free after the variable use has been
 completed

On 10/15/24 17:04, Everest K.C. wrote:
> On Tue, Oct 15, 2024 at 4:55 PM Shuah Khan <skhan@...uxfoundation.org> wrote:
>>
>> On 10/15/24 16:48, Everest K.C. wrote:
>>> On Tue, Oct 15, 2024 at 4:35 PM Shuah Khan <skhan@...uxfoundation.org> wrote:
>>>>
>>>> On 10/15/24 15:51, Everest K.C. wrote:
>>>>> The variable `in_data` is freed, but used later in the code.
>>>>> Fix it by moving the freeing the memory after it use has been
>>>>> completed.
>>>>>
>>>>> This issue was reported by Coverity Scan.
>>>>> Report:
>>>>> CID 1600783: (#1 of 1): Use after free (USE_AFTER_FREE)
>>>>> 19. pass_freed_arg: Passing freed pointer in_data as an argument to
>>>>> ni_usb_dump_raw_block.
>>>>>
>>>>> Fixes: 4e127de14fa7 ("staging: gpib: Add National Instruments USB GPIB driver")
>>>>> Signed-off-by: Everest K.C. <everestkc@...restkc.com.np>
>>>>> ---
>>>>>     drivers/staging/gpib/ni_usb/ni_usb_gpib.c | 2 +-
>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/staging/gpib/ni_usb/ni_usb_gpib.c b/drivers/staging/gpib/ni_usb/ni_usb_gpib.c
>>>>> index 1da263676f2a..75f39e1f3ed1 100644
>>>>> --- a/drivers/staging/gpib/ni_usb/ni_usb_gpib.c
>>>>> +++ b/drivers/staging/gpib/ni_usb/ni_usb_gpib.c
>>>>> @@ -690,12 +690,12 @@ static int ni_usb_read(gpib_board_t *board, uint8_t *buffer, size_t length,
>>>>>                 kfree(in_data);
>>>>>                 return parse_retval;
>>>>>         }
>>>>> -     kfree(in_data);
>>>>>         if (actual_length != length - status.count) {
>>>>>                 pr_err("%s: actual_length=%i expected=%li\n",
>>>>>                        __func__, actual_length, (long)(length - status.count));
>>>>>                 ni_usb_dump_raw_block(in_data, usb_bytes_read);
>>>>>         }
>>>>> +     kfree(in_data);
>>>>>         switch (status.error_code) {
>>>>>         case NIUSB_NO_ERROR:
>>>>>                 retval = 0;
>>>>
>>>> Looks good to me. Isn't this on next though. Don't forget to
>>>> indicate it is against next.
>>> No, it was fixed in the linux-staging repo.
>>>> Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>
>>>>
>>
>> Okay - by the way the same problem is in ni_usb_write_registers().
>> Did coverity catch that one?
> No, there were no similar issues caught by coverity.
> Also, I just checked the function. I didn't see the variable being
> accessed after
> it had been freed.

Yeah. You are right. It was out_data that was freed after
last access. in_data is fine.

thanks,
-- Shuah