Re: [PATCH] ISDN: fix copy_to_user() unused result warning in isdn_ppp

[Jesper Juhl]

On 2/22/06, Karsten Keil <kkeil@xxxxxxx> wrote:
> On Tue, Feb 21, 2006 at 11:14:15PM +0100, Jesper Juhl wrote:
> > From: Jesper Juhl <jesper.juhl@xxxxxxxxx>
> >
> >
> > Fix compile warning about copy_to_user() unused result in isdn_ppp.c
> >    drivers/isdn/i4l/isdn_ppp.c:785: warning: ignoring return value of `copy_to_user', declared with attribute warn_unused_result
> >
> >
> > Signed-off-by: Jesper Juhl <jesper.juhl@xxxxxxxxx>
> >
> > ---
> >
> >  drivers/isdn/i4l/isdn_ppp.c |    5 ++++-
> >  1 files changed, 4 insertions(+), 1 deletion(-)
> >
> > --- linux-2.6.16-rc4-mm1-orig/drivers/isdn/i4l/isdn_ppp.c     2006-01-03 04:21:10.000000000 +0100
> > +++ linux-2.6.16-rc4-mm1/drivers/isdn/i4l/isdn_ppp.c  2006-02-21 23:07:57.000000000 +0100
> > @@ -782,7 +782,10 @@ isdn_ppp_read(int min, struct file *file
> >       is->first = b;
> >
> >       spin_unlock_irqrestore(&is->buflock, flags);
> > -     copy_to_user(buf, save_buf, count);
> > +     if (copy_to_user(buf, save_buf, count)) {
> > +             kfree(save_buf);
> > +             return -EFAULT;
> > +     }
> >       kfree(save_buf);
> >
> >       return count;
>
> What about:
>
> --- linux-2.6.16-rc4-mm1-orig/drivers/isdn/i4l/isdn_ppp.c     2006-01-03 04:21:10.000000000 +0100
> +++ linux-2.6.16-rc4-mm1/drivers/isdn/i4l/isdn_ppp.c  2006-02-21 23:07:57.000000000 +0100
> @@ -782,7 +782,8 @@ isdn_ppp_read(int min, struct file *file
>         is->first = b;
>
>         spin_unlock_irqrestore(&is->buflock, flags);
> -       copy_to_user(buf, save_buf, count);
> +       if (copy_to_user(buf, save_buf, count))
> +               count = -EFAULT;
>         kfree(save_buf);
>
>         return count;
>
> should result in a conditional move instead of jumps.
>

I actually considered that, but decided against it since I thought it
would be confusing use / misuse of 'count'.

Either version is fine by me. It's not likely to get hit in any case
due to the verify_area() call further up in the code.


> But I'm OK with the original patch as well, for both version you can add
>
> Signed-off-by: Karsten Keil <kkeil@xxxxxxx>
>

Thanks.


Andrew: could you please apply either my or Karsten's version to -mm ?


--
Jesper Juhl <jesper.juhl@xxxxxxxxx>
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