linux-hardening - Re: [PATCH] Revert "bcachefs: Annotate struct bch_xattr with __counted

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Message-ID: <wsymhks7o6zbsjvac7bmi6vhjkk56ovp2vclrla64sqcquda2x@ikfk7tt76gec>
Date: Thu, 1 May 2025 15:16:55 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Alan Huang <mmpgouride@...il.com>
Cc: kees@...nel.org, gustavoars@...nel.org, thorsten.blum@...lux.com, 
	linux-bcachefs@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Revert "bcachefs: Annotate struct bch_xattr with
 __counted_by()"

On Fri, May 02, 2025 at 02:41:50AM +0800, Alan Huang wrote:
> This reverts commit 86e92eeeb23741a072fe7532db663250ff2e726a.
> 
> After the x_name, there is a value. According to the disscussion[1],
> __counted_by assumes that the flexible array member contains exactly
> the amount of elements that are specified. Now there are users came across
> buffer overflow caused by the __counted_by here[2], so revert that.
> 
> [1] https://lore.kernel.org/lkml/Zv8VDKWN1GzLRT-_@archlinux/T/#m0ce9541c5070146320efd4f928cc1ff8de69e9b2
> [2] https://privatebin.net/?a0d4e97d590d71e1#9bLmp2Kb5NU6X6cZEucchDcu88HzUQwHUah8okKPReEt
> 
> Signed-off-by: Alan Huang <mmpgouride@...il.com>
> ---
>  fs/bcachefs/xattr_format.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/bcachefs/xattr_format.h b/fs/bcachefs/xattr_format.h
> index c7916011ef34..e9f810539552 100644
> --- a/fs/bcachefs/xattr_format.h
> +++ b/fs/bcachefs/xattr_format.h
> @@ -13,7 +13,7 @@ struct bch_xattr {
>  	__u8			x_type;
>  	__u8			x_name_len;
>  	__le16			x_val_len;
> -	__u8			x_name[] __counted_by(x_name_len);
> +	__u8			x_name[];

this needs a comment, so we don't make the same mistake again

>  } __packed __aligned(8);
>  
>  #endif /* _BCACHEFS_XATTR_FORMAT_H */
> -- 
> 2.48.1
>