linux-kernel - Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in member_to

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Message-ID: <hqzhbzxbp3rjbal3z4kdwygvus76h22o2br3iwuzohgniivw5q@etyntoz75vyp>
Date: Wed, 4 Sep 2024 15:39:37 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Edward Adam Davis <eadavis@...com>
Cc: syzbot+064ce437a1ad63d3f6ef@...kaller.appspotmail.com, 
	linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in member_to_text

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");
>