Re: [PATCH v2] bcachefs: fix shift oob in alloc_lru_idx_fragmentation

[Jeongjun Park]

Alan Huang <mmpgouride@xxxxxxxxx> wrote:
>
> On Oct 21, 2024, at 23:10, Jeongjun Park <aha310510@xxxxxxxxx> wrote:
> >
> > The size of a.data_type is set abnormally large, causing shift-out-of-bounds.
> > To fix this, we need to add validation on a.data_type in
> > alloc_lru_idx_fragmentation().
> >
> > Reported-by: syzbot+7f45fa9805c40db3f108@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Fixes: 260af1562ec1 ("bcachefs: Kill alloc_v4.fragmentation_lru")
> > Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
> > ---
> > fs/bcachefs/alloc_background.h | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/fs/bcachefs/alloc_background.h b/fs/bcachefs/alloc_background.h
> > index f8e87c6721b1..91eb96b19a76 100644
> > --- a/fs/bcachefs/alloc_background.h
> > +++ b/fs/bcachefs/alloc_background.h
> > @@ -168,6 +168,9 @@ static inline bool data_type_movable(enum bch_data_type type)
> > static inline u64 alloc_lru_idx_fragmentation(struct bch_alloc_v4 a,
> >      struct bch_dev *ca)
> > {
> > + if (a.data_type > BCH_DATA_NR)
>
> This should be  >= ?

Oh, that's right. I checked it myself and it's the maximum value + 1, so
I think I should use >=.

Thanks for letting me know!

Regards,

Jeongjun Park

>
> > + return 0;
> > +
> > if (!data_type_movable(a.data_type) ||
> >    !bch2_bucket_sectors_fragmented(ca, a))
> > return 0;
> > --
>