Re: [PATCH v3] bcachefs: fix shift oob in alloc_lru_idx_fragmentation

[Hongbo Li]

On 2024/10/22 10:38, Alan Huang wrote:
> On Oct 22, 2024, at 10:26, Hongbo Li <lihongbo22@xxxxxxxxxx> wrote:
> > On 2024/10/21 23:43, Jeongjun Park 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..163a67b97a40 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)
> > > + return 0;
> > > +
> >
> > oh, I found I have done the same thing in [1]("Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in bch2_alloc_to_text"). But
>
> Your patch there is still triggering the issue.
Yeah, it just notify the issue and not prevent the issue. So I found it 
should add a.data_type condition indeed. :)
> > in my humble opinion, the validation changes also should be added. And in addition, move the condition about a.data_type into
>
> There is already the validation:
>
> bkey_fsck_err_on(alloc_data_type(a, a.data_type) != a.data_type

This is actually not enough. This only do some transition check. For 
example, if a.data_type break when bch2_bucket_sectors_dirty (the data 
corruption can lead to various situations occurring) is true, the helper 
does noting.

Thanks,
Hongbo

> And the unknown data type is already printed in bch2_prt_data_type, additional validation doesn’t help much.
>
> > data_type_movable will be better. Just my personal opinion.:)
>
> In my personal opinion, I don’t think so :)
>
> > [1] https://www.spinics.net/lists/kernel/msg5412619.html
> >
> > Thanks,
> > Hongbo
> >
> > >    if (!data_type_movable(a.data_type) ||
> > >        !bch2_bucket_sectors_fragmented(ca, a))
> > >    return 0;
> > > --