Re: [PATCH 06/20] staging/lustre: fix comparison between signed and unsigned

Greg Kroah-Hartman
2015-02-02T20:51:45Z

On Mon, Feb 02, 2015 at 03:25:58PM -0500, Oleg Drokin wrote:
> Hello!
>
> On Feb 2, 2015, at 10:44 AM, Greg Kroah-Hartman wrote:
>
> > On Mon, Feb 02, 2015 at 04:02:31PM +0300, Dan Carpenter wrote:
> >> On Sun, Feb 01, 2015 at 09:52:05PM -0500, green@linuxhacker.ru wrote:
> >>> From: Dmitry Eremin <dmitry.eremin@intel.com>
> >>>
> >>> Expression if (size != (ssize_t)size) is always false.
> >>> Therefore no bounds check errors detected.
> >>
> >> The original code actually worked as designed. The integer overflow
> >> could only happen on 32 bit systems and the test only was true for 32
> >> bit systems.
>
> Hm, indeed.
> Originally I fell into the trap thinking we are trying to protect against
> negative results here too. But in fact callers all check for the return
> to be negative as an error sign. Not to mention that we cannot overflow
> 64bit integer here as explained by the comment just 2 lines above the
> default patch context.
>
> >>
> >>> - if (size != (ssize_t)size)
> >>> + if (size > ~((size_t)0)>>1)
> >>> return -1;
> >>
> >> The problem is that the code was unclear. I think the new code is even
> >> more complicated to look at.
> > I agree, I don't even understand what the new code is doing.
>
> Sorry, this patch indeed should be dropped.
>
> > What is this code supposed to be protecting from? And -1? That should
> > never be a return value…
>
> Why is -1 a bad return value if all callsites check for that as an
> indication of error?

Because you should use "real" error values, don't make them up with
random negative numbers that mean nothing.

> (granted there's only one caller at this point in kernel space:
> lustre/llite/dir.c::ll_dir_ioctl()
> totalsize = hur_len(hur);
> OBD_FREE_PTR(hur);
> if (totalsize < 0)
> return -E2BIG;
> )

Shouldn't you have returned the error that hur_len() passed you?

thanks,

greg k-h