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

[Hongbo Li]

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.

> +		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,