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

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Date: Wed, 3 Apr 2024 16:11:22 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>, Christian Brauner <brauner@...nel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
 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 03/04/24 15:54, 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".

Yes, which (access to `f_handle`) happens here:

  48         retval = exportfs_encode_fh(path->dentry,
  49                                     (struct fid *)handle->f_handle,
  50                                     &handle_dwords, fh_flags);

> 
> Fixes: 1b43c4629756 ("fs: Annotate struct file_handle with __counted_by() and use struct_size()")
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks for catching this!
--
Gustavo

> ---
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Chuck Lever <chuck.lever@...cle.com>
> Cc: Jeff Layton <jlayton@...nel.org>
> Cc: Amir Goldstein <amir73il@...il.com>
> Cc: linux-fsdevel@...r.kernel.org
> Cc: linux-nfs@...r.kernel.org
> Cc: linux-hardening@...r.kernel.org
> ---
>   fs/fhandle.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/fs/fhandle.c b/fs/fhandle.c
> index 53ed54711cd2..08ec2340dd22 100644
> --- a/fs/fhandle.c
> +++ b/fs/fhandle.c
> @@ -40,6 +40,7 @@ static long do_sys_name_to_handle(const struct path *path,
>   			 GFP_KERNEL);
>   	if (!handle)
>   		return -ENOMEM;
> +	handle->handle_bytes = f_handle.handle_bytes;
>   
>   	/* convert handle size to multiple of sizeof(u32) */
>   	handle_dwords = f_handle.handle_bytes >> 2;