On Thu, Jun 12, 2025 at 02:19:26AM -0600, Sergio Perez Gonzalez wrote:
> In bch2_sb_members_v1_to_text() there is an incorrect size used to
> calculate the number of devices.
>
> The correct size should be `BCH_MEMBER_V1_BYTES` as implied by:
>
> static struct bch_member *members_v1_get_mut(struct bch_sb_field_members_v1
> *mi, int i)
> {
> return (void *) mi->_members + (i * BCH_MEMBER_V1_BYTES);
> }
>
> Also invert the pointers used in the calculation, given that they yield a
> negative number.
>
> Reported-by: syzbot+e577022d4fba38065...@syzkaller.appspotmail.com
> Signed-off-by: Sergio Perez Gonzalez <sperez...@gmail.com>
> ---
> fs/bcachefs/sb-members.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/fs/bcachefs/sb-members.c b/fs/bcachefs/sb-members.c
> index c673e76ca27f..cc51313ebcf6 100644
> --- a/fs/bcachefs/sb-members.c
> +++ b/fs/bcachefs/sb-members.c
> @@ -325,10 +325,10 @@ static void bch2_sb_members_v1_to_text(struct printbuf
> *out, struct bch_sb *sb,
> {
> struct bch_sb_field_members_v1 *mi = field_to_type(f, members_v1);
> struct bch_sb_field_disk_groups *gi = bch2_sb_field_get(sb,
> disk_groups);
> - int nr = (vstruct_end(&mi->field) - (void *) &gi->entries[0]) /
> sizeof(gi->entries[0]);
> + int nr = ((void *) &gi->entries[0] - vstruct_end(&mi->field)) /
> BCH_MEMBER_V1_BYTES;
>
Actually, this shouldn't be referencing gi at all - brainfart on my end,
that's a completely different superblock section. That's where the
negative number came from.
> if (nr != sb->nr_devices)
> - prt_printf(out, "nr_devices mismatch: have %i entries, should
> be %u", nr, sb->nr_devices);
> + prt_printf(out, "nr_devices mismatch: have %i entries, should
> be %u\n", nr, sb->nr_devices);
Yeah, it should have a newline.
I'll fold that in.
>
> for (int i = 0; i < nr; i++)
> member_to_text(out, members_v1_get(mi, i), gi, sb, i);
> @@ -344,10 +344,10 @@ static void bch2_sb_members_v2_to_text(struct printbuf
> *out, struct bch_sb *sb,
> {
> struct bch_sb_field_members_v2 *mi = field_to_type(f, members_v2);
> struct bch_sb_field_disk_groups *gi = bch2_sb_field_get(sb,
> disk_groups);
> - int nr = (vstruct_end(&mi->field) - (void *) &gi->entries[0]) /
> le16_to_cpu(mi->member_bytes);
> + int nr = ((void *) &gi->entries[0] - vstruct_end(&mi->field)) /
> le16_to_cpu(mi->member_bytes);
>
> if (nr != sb->nr_devices)
> - prt_printf(out, "nr_devices mismatch: have %i entries, should
> be %u", nr, sb->nr_devices);
> + prt_printf(out, "nr_devices mismatch: have %i entries, should
> be %u\n", nr, sb->nr_devices);
>
> /*
> * We call to_text() on superblock sections that haven't passed
> --
> 2.43.0
>
