linux-hardening - Re: [PATCH 2/3] scsi: esas2r: Switch to flexible array member

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Date:   Fri, 28 May 2021 15:26:18 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kees Cook <keescook@...omium.org>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Cc:     Hannes Reinecke <hare@...e.de>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Bradley Grove <linuxdrivers@...otech.com>,
        Artur Paszkiewicz <artur.paszkiewicz@...el.com>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/3] scsi: esas2r: Switch to flexible array member



On 5/28/21 13:13, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), avoid intentionally writing across
> neighboring array fields.
> 
> Remove old-style 1-byte array in favor of a flexible array[1] to avoid
> future false-positive cross-field memcpy() warning in:
> 
> esas2r_vda.c:
> 	memcpy(vi->cmd.gsv.version_info, esas2r_vdaioctl_versions, ...)
> 
> The change in struct size doesn't change other structure sizes (it is
> already maxed out to 256 bytes, for example here:
> 
>         union {
>                 struct atto_ioctl_vda_scsi_cmd scsi;
>                 struct atto_ioctl_vda_flash_cmd flash;
>                 struct atto_ioctl_vda_diag_cmd diag;
>                 struct atto_ioctl_vda_cli_cmd cli;
>                 struct atto_ioctl_vda_smp_cmd smp;
>                 struct atto_ioctl_vda_cfg_cmd cfg;
>                 struct atto_ioctl_vda_mgt_cmd mgt;
>                 struct atto_ioctl_vda_gsv_cmd gsv;
>                 u8 cmd_info[256];
>         } cmd;
> 
> No sizes are calculated using the enclosing structure, so no other
> updates are needed.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

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

Thanks
--
Gustavo

> ---
>  drivers/scsi/esas2r/atioctl.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/esas2r/atioctl.h b/drivers/scsi/esas2r/atioctl.h
> index 4aca3d52c851..ff2ad9b38575 100644
> --- a/drivers/scsi/esas2r/atioctl.h
> +++ b/drivers/scsi/esas2r/atioctl.h
> @@ -1141,7 +1141,7 @@ struct __packed atto_ioctl_vda_gsv_cmd {
>  
>  	u8 rsp_len;
>  	u8 reserved[7];
> -	u8 version_info[1];
> +	u8 version_info[];
>  	#define ATTO_VDA_VER_UNSUPPORTED 0xFF
>  
>  };
>