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

[Shuah Khan]

On 10/15/24 17:04, Everest K.C. wrote:
> On Tue, Oct 15, 2024 at 4:55 PM Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx> wrote:
> > On 10/15/24 16:48, Everest K.C. wrote:
> > > On Tue, Oct 15, 2024 at 4:35 PM Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx>
> > > > > ---
> > > > >     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@xxxxxxxxxxxxxxxxxxx>
> >
> > 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