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

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Message-ID: <aBPJ8ueDzztmDOSO@archlinux>
Date: Thu, 1 May 2025 21:22:26 +0200
From: Jan Hendrik Farr <kernel@...rr.cc>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Alan Huang <mmpgouride@...il.com>, 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 01 15:16:55, Kent Overstreet wrote:
> 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

Better yet: change x_name to x_name_and_value

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