linux-kernel - Re: [PATCH v3] smb3: Replace smb2pdu 1-element arrays with flex-arrays

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Date:   Sat, 18 Feb 2023 12:22:34 +0900
From:   Namjae Jeon <linkinjeon@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Steve French <sfrench@...ba.org>, Paulo Alcantara <pc@....nz>,
        Ronnie Sahlberg <lsahlber@...hat.com>,
        Shyam Prasad N <sprasad@...rosoft.com>,
        Tom Talpey <tom@...pey.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] smb3: Replace smb2pdu 1-element arrays with flex-arrays

2023-02-18 9:24 GMT+09:00, Kees Cook <keescook@...omium.org>:
> The kernel is globally removing the ambiguous 0-length and 1-element
> arrays in favor of flexible arrays, so that we can gain both compile-time
> and run-time array bounds checking[1].
>
> Replace the trailing 1-element array with a flexible array in the
> following structures:
>
> 	struct smb2_err_rsp
> 	struct smb2_tree_connect_req
> 	struct smb2_negotiate_rsp
> 	struct smb2_sess_setup_req
> 	struct smb2_sess_setup_rsp
> 	struct smb2_read_req
> 	struct smb2_read_rsp
> 	struct smb2_write_req
> 	struct smb2_write_rsp
> 	struct smb2_query_directory_req
> 	struct smb2_query_directory_rsp
> 	struct smb2_set_info_req
> 	struct smb2_change_notify_rsp
> 	struct smb2_create_rsp
> 	struct smb2_query_info_req
> 	struct smb2_query_info_rsp
>
> Replace the trailing 1-element array with a flexible array, but leave
> the existing structure padding:
>
> 	struct smb2_file_all_info
> 	struct smb2_lock_req
>
> Adjust all related size calculations to match the changes to sizeof().
>
> No machine code output or .data section differences are produced after
> these changes.
>
> [1] For lots of details, see both:
>
> https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
>     https://people.kernel.org/kees/bounded-flexible-arrays-in-c
>
> Cc: Steve French <sfrench@...ba.org>
> Cc: Paulo Alcantara <pc@....nz>
> Cc: Ronnie Sahlberg <lsahlber@...hat.com>
> Cc: Shyam Prasad N <sprasad@...rosoft.com>
> Cc: Tom Talpey <tom@...pey.com>
> Cc: Namjae Jeon <linkinjeon@...nel.org>
> Cc: Sergey Senozhatsky <senozhatsky@...omium.org>
> Cc: linux-cifs@...r.kernel.org
> Cc: samba-technical@...ts.samba.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Namjae Jeon <linkinjeon@...nel.org>

Thanks!