Re: [PATCH] vfs: fix statfs64() returning impossible EOVERFLOW for 64-bit f_files

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Sergey Klyaus <sergey.m.klyaus@gmail.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Li Wang <liwang@redhat.com>, Andreas Dilger <adilger@dilger.ca>,
	Andi Kleen <andi.kleen@intel.com>
Subject: Re: [PATCH] vfs: fix statfs64() returning impossible EOVERFLOW for 64-bit f_files
Date: Thu, 5 Oct 2017 15:31:05 -0700	[thread overview]
Message-ID: <CA+55aFx7d2+GG=0LqMejiK=ZADxX347v_m0S4WzrnQ=1FoyP8A@mail.gmail.com> (raw)
In-Reply-To: <20171005205724.GJ21978@ZenIV.linux.org.uk>

On Thu, Oct 5, 2017 at 1:57 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> AFAICS, the real bug here is in hugetlbfs; that's where obscene values in
> ->f_bsize come from.  IMO all that code in put_compat_statfs64() should be
> replaced with
>         if (kbuf->bsize != (u32)kbuf->bsize)
>                 return -EOVERFLOW;
> That, or hugetlbfs could be taught to fake saner ->f_bsize (recalculating
> ->f_bavail/->f_bfree/->f_blocks to go with that).

Make it so. Except you shouldn't do

     if (kbuf->bsize != (u32)kbuf->bsize)

you should do something like

    #define FITS_IN(x,y)  ({ typeof x __x = (x); typeof y __y = __x;
__x == __y; })

and then do

    if (!FITS_IN(kbuf->bsize, ubuf->bsize)) ...

because there is nothing that specifies that the ubuf size of all
fields has to be 32 bits.

But yes,m either you need to then special-case that crazy all-ones
value, or just fix hugetlbfs to not use crazy crap.

                  Linus