Re: [PATCH v2] bcachefs: Fix shift-out-of-bounds in bch2_stripe_to_text

[Hongbo Li]

On 2024/10/9 17:10, Hongbo Li wrote:
> On 2024/10/9 13:43, Zhao Mengmeng wrote:
> > From: Zhao Mengmeng <zhaomengmeng@xxxxxxxxxx>
> >
> > syzbot report a shift-out-of-bounds issue:
> > ------------[ cut here ]------------
> > UBSAN: shift-out-of-bounds in fs/bcachefs/ec.c:147:2
> > shift exponent 108 is too large for 32-bit type 'unsigned int'
> > ----
> > Here s.csum_granularity_bits = 108, so shift is impossible for unsigned
> > int. To fix, add a check in bch2_stripe_validate() to bail out, it has
> > same checking logic with ec_stripe_key_init().
> >
> > Reported-by: syzbot+f8c98a50c323635be65d@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Tested-by: syzbot+f8c98a50c323635be65d@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Closes: https://syzkaller.appspot.com/bug?extid=f8c98a50c323635be65d
> > Suggested-by: Hongbo Li <lihongbo22@xxxxxxxxxx>
> > Signed-off-by: Zhao Mengmeng <zhaomengmeng@xxxxxxxxxx>
> > ---
> >   fs/bcachefs/ec.c      | 6 ++++++
> >   fs/bcachefs/errcode.h | 3 ++-
> >   2 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/bcachefs/ec.c b/fs/bcachefs/ec.c
> > index 141a4c63142f..bc5ff1331c6f 100644
> > --- a/fs/bcachefs/ec.c
> > +++ b/fs/bcachefs/ec.c
> > @@ -113,6 +113,12 @@ int bch2_stripe_validate(struct bch_fs *c, struct 
> > bkey_s_c k,
> >       const struct bch_stripe *s = bkey_s_c_to_stripe(k).v;
> >       int ret = 0;
> > +    if (s->csum_granularity_bits >= ilog2(le16_to_cpu(s->sectors))) {
>
> csum_granularity_bits should do the left shift.
oh no, I miss your ilog2 helper.
> > +        bch_err_ratelimited(c, "stripe csum gran bits %u too big",
> > +                    s->csum_granularity_bits);
> > +        return -BCH_ERR_stripe_csum_granularity_bits_too_big;
> > +    }
> > +
> >       bkey_fsck_err_on(bkey_eq(k.k->p, POS_MIN) ||
> >                bpos_gt(k.k->p, POS(0, U32_MAX)),
> >                c, stripe_pos_bad,
> > diff --git a/fs/bcachefs/errcode.h b/fs/bcachefs/errcode.h
> > index 742dcdd3e5d7..14ba6bc7a029 100644
> > --- a/fs/bcachefs/errcode.h
> > +++ b/fs/bcachefs/errcode.h
> > @@ -258,7 +258,8 @@
> >       x(BCH_ERR_nopromote,        nopromote_no_writes)            \
> >       x(BCH_ERR_nopromote,        nopromote_enomem)            \
> >       x(0,                invalid_snapshot_node)            \
> > -    x(0,                option_needs_open_fs)
> > +    x(0,                option_needs_open_fs)            \
> There are some changes, this should rebase on the latest tree.
>
> Thanks,
> Hongbo
> > +    x(EINVAL,            stripe_csum_granularity_bits_too_big)
> >   enum bch_errcode {
> >       BCH_ERR_START        = 2048,