linux-hardening - Re: [PATCH v2] smb3: Replace smb2pdu 1-element arrays with flex-arrays

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Message-ID: <63f01810.170a0220.110a8.6fe1@mx.google.com>
Date:   Fri, 17 Feb 2023 16:13:03 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Namjae Jeon <linkinjeon@...nel.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, linux-kernel@...r.kernel.org,
        samba-technical@...ts.samba.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] smb3: Replace smb2pdu 1-element arrays with
 flex-arrays

On Thu, Feb 16, 2023 at 11:25:01PM +0900, Namjae Jeon wrote:
> Hi Kees,
> 
> >  /* Read flags */
> > @@ -730,7 +730,7 @@ struct smb2_read_rsp {
> >  	__le32 DataLength;
> >  	__le32 DataRemaining;
> >  	__le32 Flags;
> > -	__u8   Buffer[1];
> > +	__u8   Buffer[];
> >  } __packed;
> >
> 
> You seem to have missed -1 removal in the code below.

Ah; thanks for this heads-up. I will need a v3.

> ./fs/cifs/smb2ops.c:5632:       .read_rsp_size = sizeof(struct
> smb2_read_rsp) - 1,
> ./fs/cifs/smb2ops.c:5654:       .read_rsp_size = sizeof(struct
> smb2_read_rsp) - 1,
...

These are interesting -- they don't show up at all in the code. What I
mean is that they're data-only changes. I'll add that to my before/after
build sanity checks.

Thanks!

-Kees

-- 
Kees Cook