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Date:   Thu, 1 Sep 2022 14:34:23 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        syzbot <syzkaller@googlegroups.com>,
        netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        netdev@vger.kernel.org,
        Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH v3] netlink: Bounds-check struct nlmsgerr creation
Message-ID: <20220901143423.2abc0ab0@kernel.org>
In-Reply-To: <20220901071336.1418572-1-keescook@chromium.org>
References: <20220901071336.1418572-1-keescook@chromium.org>
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On Thu,  1 Sep 2022 00:13:36 -0700 Kees Cook wrote:
>  	rep = __nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq,
>  			  NLMSG_ERROR, payload, flags);

All we should need here is __nlmsg_put() -> nlmsg_put(),
that's idiomatic for netlink.

>  	errmsg = nlmsg_data(rep);
>  	errmsg->error = err;
> -	memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh));
> +	unsafe_memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg)
> +					 ?  nlh->nlmsg_len : sizeof(*nlh),
> +		      /* "payload" was bounds checked against nlh->nlmsg_len,
> +		       * and overflow-checked as tlvlen was constructed.
> +		       */);