Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in member_to_text

[Kent Overstreet]

On Tue, Sep 03, 2024 at 10:13:02AM GMT, Edward Adam Davis wrote:
> Because the value of m.btree_bitmap_shift is 69 in this case, it cause 
> shift-out-of-bounds in member_to_text.
> 
> Add a check for btree_bitmap_shift in validate_member, when it bigger than 64
> return -BCH_ERR_invalid_sb_members.
> Simultaneously adjust the output mode of btree_bitmap_shift in member_to_text. 
> 
> #syz test
> 
> diff --git a/fs/bcachefs/sb-members.c b/fs/bcachefs/sb-members.c
> index 39196f2a4197..85a4245ea6a3 100644
> --- a/fs/bcachefs/sb-members.c
> +++ b/fs/bcachefs/sb-members.c
> @@ -162,6 +162,12 @@ static int validate_member(struct printbuf *err,
>  		return -BCH_ERR_invalid_sb_members;
>  	}
>  
> +	if (m.btree_bitmap_shift > 64) {

should be >=, no?

> +		prt_printf(err, "device %u: too many big bitmap shift (got %u, max 64)",
> +			   i, m.btree_bitmap_shift);
> +		return -BCH_ERR_invalid_sb_members;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -245,8 +251,7 @@ static void member_to_text(struct printbuf *out,
>  		prt_printf(out, "(none)");
>  	prt_newline(out);
>  
> -	prt_printf(out, "Btree allocated bitmap blocksize:\t");
> -	prt_units_u64(out, 1ULL << m.btree_bitmap_shift);
> +	prt_printf(out, "Btree allocated bitmap shift: %d\t", m.btree_bitmap_shift);
>  	prt_newline(out);
>  
>  	prt_printf(out, "Btree allocated bitmap:\t");
>