linux-kernel - Re: Linux 6.2-rc1

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Date:   Fri, 6 Jan 2023 16:06:00 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Kees Cook <kees@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chao Yu <chao@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: Linux 6.2-rc1

On 12/28, Guenter Roeck wrote:
> On Tue, Dec 27, 2022 at 07:40:30PM -0800, Kees Cook wrote:
> > On December 26, 2022 9:52:12 PM PST, Guenter Roeck <linux@...ck-us.net> wrote:
> > >On Mon, Dec 26, 2022 at 05:32:28PM -0800, Kees Cook wrote:
> > >> On December 26, 2022 4:29:41 PM PST, Guenter Roeck <linux@...ck-us.net> wrote:
> > >> >On Mon, Dec 26, 2022 at 01:03:59PM -0800, Kees Cook wrote:
> > >> >> On December 26, 2022 12:56:29 PM PST, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > >> >> >On Mon, Dec 26, 2022 at 11:52 AM Guenter Roeck <linux@...ck-us.net> wrote:
> > >> >> >>
> > >> >> >> fs/f2fs/inline.c: In function 'f2fs_move_inline_dirents':
> > >> >> >> include/linux/fortify-string.h:59:33: error: '__builtin_memset' pointer overflow between offset [28, 898293814] and size [-898293787, -1] [-Werror=array-bounds]
> > >> >> >> fs/f2fs/inline.c:430:9: note: in expansion of macro 'memset'
> > >> >> >>   430 |         memset(dst.bitmap + src.nr_bitmap, 0, dst.nr_bitmap - src.nr_bitmap);
> > >> >> >>       |         ^~~~~~
> > >> >> >
> > >> >> >Well, that's unfortunate.
> > >> >> 
> > >> >> I'll look into this.
> > >> >> 
> > >> >
> > >> >I did some more testing. The problem is seen with gcc 11.3.0, but not with
> > >> >gcc 12.2.0 nor with gcc 10.3.0.
> > >> 
> > >> That's what I'd expect: 10 didn't have variable range tracking wired up to -Warray-bounds, 11 does, and we disable -Warray-bounds on 12 because of 3 separate 12-only GCC bugs.
> > >> 
> > >> > gcc bug ? Should I switch to gcc 12.2.0 for
> > >> >powerpc when build testing the latest kernel ?
> > >> 
> > >> Sure? But that'll just hide it. I suspect GCC has found a way for dst.nr_bitmap to be compile-time 27, so the size is always negative.
> > >> 
> > >dst.nr_bitmap is initialized with SIZE_OF_DENTRY_BITMAP,
> > >which is defined as:
> > >
> > >#define NR_DENTRY_IN_BLOCK      214     /* the number of dentry in a block */
> > >#define SIZE_OF_DIR_ENTRY       11      /* by byte */
> > >#define SIZE_OF_DENTRY_BITMAP   ((NR_DENTRY_IN_BLOCK + BITS_PER_BYTE - 1) / \
> > >                                        BITS_PER_BYTE)
> > >
> > >((214 + 8 - 1) / 8 = 27, so dst.nr_bitmap is indeed compile-time 27.
> > >
> > >Not sure how would know that src.nr_bitmap can be > 27, though.
> > >Am I missing something ?
> > 
> > I think it's saying it can't rule out it being larger? I.e. there is no obvious bounds checking for it. Perhaps:
> > 
> > if (src.nr_bitmap > dst.nr_bitmap) {
> >     err = -EFSCORRUPTED;
> > 		goto out;
> > }
> > 
> 
> After going through all calculations, using maximum values (or minimum
> values where appropriate) everywhere, I calculated that src.nr_bitmap
> is always <= 24. The actual inode is sanity checked in
> fs/f2fs/inode.c:sanity_check_inode().

I also cannot find any case where src.nr_bitmap > 24. May this be a GCC issue?

> 
> Also, why is this only seen when I try to build powerpc test images ?
> 
> Thanks,
> Guenter