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

[Hongbo Li]

On 2024/10/9 17:16, Zhao Mengmeng wrote:
> 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.
>
> If use `1 << s->csum_granularity_bits(108)` to do the check, syzbot will still trigger shift-out-of
> bounds warning. So better check the bits directly.
You are right! :)

Thanks
Hongbo