Re: [PATCH] fs/ntfs3: fix negative shift size in true_sectors_per_clst()

[Konstantin Komarov]

On 9/23/22 03:38, Randy Dunlap wrote:
> Hi,
>
> On 9/20/22 08:59, Tetsuo Handa wrote:
> > syzbot is reporting shift-out-of-bounds in true_sectors_per_clst() [1], for
> > commit a3b774342fa752a5 ("fs/ntfs3: validate BOOT sectors_per_clusters")
> > did not address that (0 - boot->sectors_per_clusters) < 0 because "u8" was
> > chosen for type of boot->sectors_per_clusters because 0x80 needs to be
> > positive in order to support 64K clusters. Use "s8" cast in order to make
> > sure that (0 - (s8) boot->sectors_per_clusters) > 0.
> >
> > Link: https://syzkaller.appspot.com/bug?extid=1631f09646bc214d2e76 [1]
> > Reported-by: syzbot <syzbot+1631f09646bc214d2e76@xxxxxxxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Tested-by: syzbot <syzbot+1631f09646bc214d2e76@xxxxxxxxxxxxxxxxxxxxxxxxx>
> > Fixes: a3b774342fa752a5 ("fs/ntfs3: validate BOOT sectors_per_clusters")
> >
> > diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
> > index 47012c9bf505..c7ffd21fb255 100644
> > --- a/fs/ntfs3/super.c
> > +++ b/fs/ntfs3/super.c
> > @@ -672,7 +672,7 @@ static u32 true_sectors_per_clst(const struct NTFS_BOOT *boot)
> >   	if (boot->sectors_per_clusters <= 0x80)
> >   		return boot->sectors_per_clusters;
> >   	if (boot->sectors_per_clusters >= 0xf4) /* limit shift to 2MB max */
> > -		return 1U << (0 - boot->sectors_per_clusters);
> > +		return 1U << (0 - (s8) boot->sectors_per_clusters);
> >   	return -EINVAL;
> >   }
> >   
>
> I slightly prefer the earlier patch:
>
> https://lore.kernel.org/all/20220823144625.1627736-1-syoshida@xxxxxxxxxx/
>
> but it appears that the NTFS3 maintainer is MIA again. :(

Hello

I've sent patches on 12.09, so I'm not MIA.
I plan to look at patches next week, there are quite a lot of them.