linux-kernel - Re: [PATCH V2] staging: gpib: Remove a dead condition in if statement

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Message-ID: <2024101749-refocus-making-51b2@gregkh>
Date: Thu, 17 Oct 2024 08:01:14 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: "Everest K.C." <everestkc@...restkc.com.np>
Cc: dpenkler@...il.com, skhan@...uxfoundation.org,
	linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] staging: gpib: Remove a dead condition in if statement

On Wed, Oct 16, 2024 at 10:42:03PM -0600, Everest K.C. wrote:
> On Wed, Oct 16, 2024 at 8:50 PM Everest K.C. <everestkc@...restkc.com.np> wrote:
> >
> > On Wed, Oct 16, 2024 at 9:12 AM Greg KH <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Wed, Oct 16, 2024 at 06:54:00AM -0600, Everest K.C. wrote:
> > > > On Wed, Oct 16, 2024 at 2:04 AM Greg KH <gregkh@...uxfoundation.org> wrote:
> > > > >
> > > > > On Wed, Oct 16, 2024 at 01:53:18AM -0600, Everest K.C. wrote:
> > > > > > The variable `residue` is an unsigned int, also the function
> > > > > > `fluke_get_dma_residue` returns an unsigned int. The value of
> > > > > > an unsigned int can only be 0 at minimum.
> > > > > > The less-than-zero comparison can never be true.
> > > > > > Fix it by removing the dead condition in the if statement.
> > > > > >
> > > > > > This issue was reported by Coverity Scan.
> > > > > > Report:
> > > > > > CID 1600782: (#1 of 1): Macro compares unsigned to 0 (NO_EFFECT)
> > > > > > unsigned_compare: This less-than-zero comparison of an unsigned value
> > > > > > is never true. residue < 0U.
> > > > > >
> > > > > > Signed-off-by: Everest K.C. <everestkc@...restkc.com.np>
> > > > > > ---
> > > > > > V1 -> V2: - Fixed typo of comparison in changelog
> > > > > >           - Removed Fixes tag
> > > > > >
> > > > > >  drivers/staging/gpib/eastwood/fluke_gpib.c | 2 +-
> > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/drivers/staging/gpib/eastwood/fluke_gpib.c b/drivers/staging/gpib/eastwood/fluke_gpib.c
> > > > > > index f9f149db222d..51b4f9891a34 100644
> > > > > > --- a/drivers/staging/gpib/eastwood/fluke_gpib.c
> > > > > > +++ b/drivers/staging/gpib/eastwood/fluke_gpib.c
> > > > > > @@ -644,7 +644,7 @@ static int fluke_dma_read(gpib_board_t *board, uint8_t *buffer,
> > > > > >        */
> > > > > >       usleep_range(10, 15);
> > > > > >       residue = fluke_get_dma_residue(e_priv->dma_channel, dma_cookie);
> > > > > > -     if (WARN_ON_ONCE(residue > length || residue < 0))
> > > > > > +     if (WARN_ON_ONCE(residue > length))
> > > > >
> > > > > No, this is incorrect, now we never notice is the call to
> > > > > fluke_get_dma_residue() has failed.  Please fix that bug instead (hint,
> > > > > Covertity is giving you a pointer to where something might be wrong, but
> > > > > this change is NOT how to fix it.)
> > > > I need a little guidance here.
> > > > My best guess to fix the bug would be to make fluke_get_dma_residue()
> > > > return an int instead of unsigned int or size_t. But theoretically the
> > > > maximum value of residue can be UINT_MAX, and casting it to int will
> > > > result in a negative number, which in turn will cause  the error check
> > > > condition to evaluate to true.
> > >
> > > Look at the code to see what it does.
> > >
> > > > The best solution I see would be to make fluke_get_dma_residue() return
> > > > an int (-1 for error and 0 for success). Then pass the address of residue
> > > > reference to fluke_get_dma_residue() to be updated.
> > > > Am I on the right track ?
> > >
> > > Close, yes.  "-1" is not a valid error, so that needs to be fixed at the
> > > least here, as it's obviously not returning an error that gets caught
> > > today :)
> > Noted. Thank you very much.
> > I have a question though. Since, the file I had previously fixed (which
> > was incorrect) and the file I now need to fix are different. Should I create
> > a new patch that would be of version 1, or should I send a V2 ?
> Oops, it's in the same file but my question still stands, should I send a new
> patch or V2 revision ?

Probably a new patch if it has a totally different subject line.

thanks,

greg k-h