linux-hardening - Re: [PATCH] s390: iucv: Avoid field over-reading memcpy()

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Date:   Tue, 29 Jun 2021 17:19:50 +0200
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     Kees Cook <keescook@...omium.org>,
        Heiko Carstens <hca@...ux.ibm.com>
Cc:     Julian Wiedmann <jwi@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] s390: iucv: Avoid field over-reading memcpy()

On 16/06/2021 22:19, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally reading across neighboring array fields.
> 
> Add a wrapping struct to serve as the memcpy() source so the compiler
> can perform appropriate bounds checking, avoiding this future warning:
> 
> In function '__fortify_memcpy',
>     inlined from 'iucv_message_pending' at net/iucv/iucv.c:1663:4:
> ./include/linux/fortify-string.h:246:4: error: call to '__read_overflow2_field' declared with attribute error: detected read beyond size of field (2nd parameter)
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

Looks good, thanks for taking care of that change.

Acked-by: Karsten Graul <kgraul@...ux.ibm.com>

> ---
>  net/iucv/iucv.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/net/iucv/iucv.c b/net/iucv/iucv.c
> index 349c6ac3313f..e6795d5a546a 100644
> --- a/net/iucv/iucv.c
> +++ b/net/iucv/iucv.c
> @@ -1635,14 +1635,16 @@ struct iucv_message_pending {
>  	u8  iptype;
>  	u32 ipmsgid;
>  	u32 iptrgcls;
> -	union {
> -		u32 iprmmsg1_u32;
> -		u8  iprmmsg1[4];
> -	} ln1msg1;
> -	union {
> -		u32 ipbfln1f;
> -		u8  iprmmsg2[4];
> -	} ln1msg2;
> +	struct {
> +		union {
> +			u32 iprmmsg1_u32;
> +			u8  iprmmsg1[4];
> +		} ln1msg1;
> +		union {
> +			u32 ipbfln1f;
> +			u8  iprmmsg2[4];
> +		} ln1msg2;
> +	} rmmsg;
>  	u32 res1[3];
>  	u32 ipbfln2f;
>  	u8  ippollfg;
> @@ -1660,10 +1662,10 @@ static void iucv_message_pending(struct iucv_irq_data *data)
>  		msg.id = imp->ipmsgid;
>  		msg.class = imp->iptrgcls;
>  		if (imp->ipflags1 & IUCV_IPRMDATA) {
> -			memcpy(msg.rmmsg, imp->ln1msg1.iprmmsg1, 8);
> +			memcpy(msg.rmmsg, &imp->rmmsg, 8);
>  			msg.length = 8;
>  		} else
> -			msg.length = imp->ln1msg2.ipbfln1f;
> +			msg.length = imp->rmmsg.ln1msg2.ipbfln1f;
>  		msg.reply_size = imp->ipbfln2f;
>  		path->handler->message_pending(path, &msg);
>  	}
> 

-- 
Karsten

(I'm a dude)