linux-kernel - Re: [PATCH] fs/cifs: Replace one-element array with flexible-array member.

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Message-ID: <20210118000152.GH3579531@ZenIV.linux.org.uk>
Date:   Mon, 18 Jan 2021 00:01:52 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Steve French <smfrench@...il.com>
Cc:     Aurélien Aptel <aaptel@...e.com>,
        Jiapeng Zhong <abaci-bugfix@...ux.alibaba.com>,
        Steve French <sfrench@...ba.org>,
        CIFS <linux-cifs@...r.kernel.org>,
        samba-technical <samba-technical@...ts.samba.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs/cifs: Replace one-element array with flexible-array
 member.

On Sun, Jan 17, 2021 at 03:58:23PM -0600, Steve French wrote:
> Jiapeng,
> Aurelien is correct, you should respin this patch and correct for
> where it breaks the sizeof calculation.  For example your change:
> 
> struct smb2_lock_rsp {
> @@ -1434,7 +1434,7 @@ struct smb2_query_directory_req {
>         __le16 FileNameOffset;
>         __le16 FileNameLength;
>         __le32 OutputBufferLength;
> -       __u8   Buffer[1];
> +       __u8   Buffer[];
>  } __packed;
> 
> would have the side effect of making the file name off by one:
> 
> smb2pdu.c-4654- req->FileNameOffset =
> smb2pdu.c:4655:         cpu_to_le16(sizeof(struct
> smb2_query_directory_req) - 1);

FWIW, that sizeof() - 1 should've been offsetof()...