On Thu, Oct 24, 2024 at 12:48:30PM +0200, Gianfranco Trad wrote:
> On 23/10/24 23:30, Gianfranco Trad wrote:
> > Add check on layout->sb_max_size_bits against BCH_SB_LAYOUT_SIZE_BITS_MAX
> > to prevent UBSAN shift-out-of-bounds in validate_sb_layout().
> >
> > Reported-by: [email protected]
> > Closes: https://syzkaller.appspot.com/bug?extid=089fad5a3a5e77825426
> > Fixes: 03ef80b469d5 ("bcachefs: Ignore unknown mount options")
> > Tested-by: [email protected]
> > Signed-off-by: Gianfranco Trad <[email protected]>
> > ---
> > fs/bcachefs/errcode.h | 1 +
> > fs/bcachefs/super-io.c | 5 +++++
> > 2 files changed, 6 insertions(+)
> >
> > diff --git a/fs/bcachefs/errcode.h b/fs/bcachefs/errcode.h
> > index 649263516ab1..b6cbd716000b 100644
> > --- a/fs/bcachefs/errcode.h
> > +++ b/fs/bcachefs/errcode.h
> > @@ -222,6 +222,7 @@
> > x(BCH_ERR_invalid_sb_layout, invalid_sb_layout_type)
> > \
> > x(BCH_ERR_invalid_sb_layout, invalid_sb_layout_nr_superblocks)
> > \
> > x(BCH_ERR_invalid_sb_layout, invalid_sb_layout_superblocks_overlap)
> > \
> > + x(BCH_ERR_invalid_sb_layout, invalid_sb_layout_sb_max_size_bits)
> > \
> > x(BCH_ERR_invalid_sb, invalid_sb_members_missing)
> > \
> > x(BCH_ERR_invalid_sb, invalid_sb_members)
> > \
> > x(BCH_ERR_invalid_sb, invalid_sb_disk_groups)
> > \
> > diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
> > index ce7410d72089..44d0ac9b00dd 100644
> > --- a/fs/bcachefs/super-io.c
> > +++ b/fs/bcachefs/super-io.c
> > @@ -287,6 +287,11 @@ static int validate_sb_layout(struct bch_sb_layout
> > *layout, struct printbuf *out
> > return -BCH_ERR_invalid_sb_layout_nr_superblocks;
> > }
> > + if (layout->sb_max_size_bits > BCH_SB_LAYOUT_SIZE_BITS_MAX) {
> > + prt_printf(out, "Invalid superblock layout: max_size_bits too
> > high");
> > + return -BCH_ERR_invalid_sb_layout_sb_max_size_bits;
> > + }
> > +
> > max_sectors = 1 << layout->sb_max_size_bits;
> > prev_offset = le64_to_cpu(layout->sb_offset[0]);
>
> Wondering if this other patch might be considered more correct to prevent
> shift oob, given also [0]:
Your first patch looks better, we want to know if we're feeding it
garbage
>
> diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
> index ce7410d72089..428172897501 100644
> --- a/fs/bcachefs/super-io.c
> +++ b/fs/bcachefs/super-io.c
> @@ -287,7 +287,7 @@ static int validate_sb_layout(struct bch_sb_layout
> *layout, struct printbuf *out
> return -BCH_ERR_invalid_sb_layout_nr_superblocks;
> }
>
> - max_sectors = 1 << layout->sb_max_size_bits;
> + max_sectors = 1 << min(BCH_SB_LAYOUT_SIZE_BITS_MAX,
> layout->sb_max_size_bits);
>
> prev_offset = le64_to_cpu(layout->sb_offset[0]);
>
> Also this patch was already tested by syzbot [1]
>
> [0] 71dac2482ad3c8d4a8b8998a96751f009bad895f ("bcachefs:
> BCH_SB_LAYOUT_SIZE_BITS_MAX")
> [1] https://syzkaller.appspot.com/x/log.txt?x=1640b640580000
>
> Thanks for your time,
>
> -- Gian
>
>
>
>
>
