linux-hardening - Re: [PATCH] fs: Set file_handle::handle_bytes before referencing file_handle::f

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Message-ID: <20240405-imponieren-scheppern-5e6b6842ccbf@brauner>
Date: Fri, 5 Apr 2024 13:00:27 +0200
From: Christian Brauner <brauner@...nel.org>
To: Jan Kara <jack@...e.cz>
Cc: Kees Cook <keescook@...omium.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Chuck Lever <chuck.lever@...cle.com>, Jeff Layton <jlayton@...nel.org>, 
	Amir Goldstein <amir73il@...il.com>, linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org, 
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: Set file_handle::handle_bytes before referencing
 file_handle::f_handle

On Thu, Apr 04, 2024 at 11:19:00AM +0200, Jan Kara wrote:
> On Wed 03-04-24 14:54:03, Kees Cook wrote:
> > With adding __counted_by(handle_bytes) to struct file_handle, we need
> > to explicitly set it in the one place it wasn't yet happening prior to
> > accessing the flex array "f_handle".
> > 
> > Fixes: 1b43c4629756 ("fs: Annotate struct file_handle with __counted_by() and use struct_size()")
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> OK, so this isn't really a functional bug AFAIU but the compiler will
> wrongly complain we are accessing handle->f_handle beyond claimed array
> size (because handle->handle_bytes == 0 at that point). Am I right? If

And really, this also needs to please be mentioned in the commit message
because from reading the commit message I'm not even sure what this
patch is trying to fix.