From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 10B49374F0 for ; Mon, 9 Oct 2023 16:01:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="D6leI24v" Received: from mail-pf1-x431.google.com (mail-pf1-x431.google.com [IPv6:2607:f8b0:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 56251B7 for ; Mon, 9 Oct 2023 09:01:37 -0700 (PDT) Received: by mail-pf1-x431.google.com with SMTP id d2e1a72fcca58-690bf8fdd1aso3375557b3a.2 for ; Mon, 09 Oct 2023 09:01:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1696867297; x=1697472097; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=fIq4Z5Y2KCiwFjSNvRCcRrRGWFulfAYmkI5Tl6YV8HY=; b=D6leI24vqLEOAn243F2jarb07Fa5no+OEmqLI+jsm7APEM85NtiL6Wjq61JeneHWJL SOdmBVHeqmruX8hTNsJXqZ12Rkwqj4dIDDMBZqtAofFT5Ht5fOqTgrLXyL2/qm0IbYcW duzUhu9xUJeySDjBvIeXCEREkkwulTX6rCQwc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696867297; x=1697472097; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=fIq4Z5Y2KCiwFjSNvRCcRrRGWFulfAYmkI5Tl6YV8HY=; b=cVpdu6pDlEOyaC+00VVGEhx/Aj9EFhaKev6Hl4yL0A+wSUsAQQnumvK1nJbU41nm2J PnwmHCwJG8enY05cHskz8O3mv4OlQCdMMIde1ZkUxKhroa9E9ljafma1YFYyroXS8oRF tbqRz2bNUrYB5y8dMydKK+NUcu4hPaNA0ylRZK6AJPQvEpjgpilgp74ESLE9HOSjIGaP 14XTQokJr8ZbomdTv1CR6evrY1wckO5TEs8modsO0xsb2YPlX/ArSpsD7iGxsTUP8AzD UwH8FmqSDE9ALbtYvZkJe6aRlzQO1RzmferD/F8gt3ebhY5y5Su27C+XDf0lRjEudGPR tY5w== X-Gm-Message-State: AOJu0YxUAj/ESp3qsJkZIKBWy9LwbR7Fl5LJHQlaOu/FnveGr1HLIvJX jdawaY+k/fkKxgV6BS228IpuKg== X-Google-Smtp-Source: AGHT+IGzWMhg2YBxKZpnPCicy+u6EYSsmxQ4VBOiMQgc178btuiuE2aejaE6C1t+/qa5G4gqgzNYNw== X-Received: by 2002:a05:6a00:99c:b0:68f:cc67:e723 with SMTP id u28-20020a056a00099c00b0068fcc67e723mr16129844pfg.17.1696867296723; Mon, 09 Oct 2023 09:01:36 -0700 (PDT) Received: from www.outflux.net (198-0-35-241-static.hfc.comcastbusiness.net. [198.0.35.241]) by smtp.gmail.com with ESMTPSA id r19-20020aa78453000000b00688965c5227sm6574028pfn.120.2023.10.09.09.01.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Oct 2023 09:01:36 -0700 (PDT) Date: Mon, 9 Oct 2023 09:01:34 -0700 From: Kees Cook To: Kuniyuki Iwashima Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Willem de Bruijn , Simon Horman , Kuniyuki Iwashima , netdev@vger.kernel.org, Sergei Trofimovich Subject: Re: [PATCH v1 net] af_packet: Fix fortified memcpy() without flex array. Message-ID: <202310090852.E9A6558@keescook> References: <20231009153151.75688-1-kuniyu@amazon.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231009153151.75688-1-kuniyu@amazon.com> X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Mon, Oct 09, 2023 at 08:31:52AM -0700, Kuniyuki Iwashima wrote: > Sergei Trofimovich reported a regression [0] caused by commit a0ade8404c3b > ("af_packet: Fix warning of fortified memcpy() in packet_getname()."). > > It introduced a flex array sll_addr_flex in struct sockaddr_ll as a > union-ed member with sll_addr to work around the fortified memcpy() check. > > However, a userspace program uses a struct that has struct sockaddr_ll in > the middle, where a flex array is illegal to exist. > > include/linux/if_packet.h:24:17: error: flexible array member 'sockaddr_ll::::::sll_addr_flex' not at end of 'struct packet_info_t' > 24 | __DECLARE_FLEX_ARRAY(unsigned char, sll_addr_flex); > | ^~~~~~~~~~~~~~~~~~~~ > To fix the regression, let's go back to the first attempt [1] telling > memcpy() the actual size of the array. > > Reported-by: Sergei Trofimovich > Closes: https://github.com/NixOS/nixpkgs/pull/252587#issuecomment-1741733002 [0] Eww. That's a buggy definition -- it could get overflowed. But okay, we don't break userspace. > Link: https://lore.kernel.org/netdev/20230720004410.87588-3-kuniyu@amazon.com/ [1] > Fixes: a0ade8404c3b ("af_packet: Fix warning of fortified memcpy() in packet_getname().") > Signed-off-by: Kuniyuki Iwashima > --- > include/uapi/linux/if_packet.h | 6 +----- > net/packet/af_packet.c | 7 ++++++- > 2 files changed, 7 insertions(+), 6 deletions(-) > > diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h > index 4d0ad22f83b5..9efc42382fdb 100644 > --- a/include/uapi/linux/if_packet.h > +++ b/include/uapi/linux/if_packet.h > @@ -18,11 +18,7 @@ struct sockaddr_ll { > unsigned short sll_hatype; > unsigned char sll_pkttype; > unsigned char sll_halen; > - union { > - unsigned char sll_addr[8]; > - /* Actual length is in sll_halen. */ > - __DECLARE_FLEX_ARRAY(unsigned char, sll_addr_flex); > - }; > + unsigned char sll_addr[8]; > }; Yup, we need to do at least this. > > /* Packet types */ > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index 8f97648d652f..a84e00b5904b 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -3607,7 +3607,12 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr, > if (dev) { > sll->sll_hatype = dev->type; > sll->sll_halen = dev->addr_len; > - memcpy(sll->sll_addr_flex, dev->dev_addr, dev->addr_len); > + > + /* Let __fortify_memcpy_chk() know the actual buffer size. */ > + memcpy(((struct sockaddr_storage *)sll)->__data + > + offsetof(struct sockaddr_ll, sll_addr) - > + offsetofend(struct sockaddr_ll, sll_family), > + dev->dev_addr, dev->addr_len); > } else { > sll->sll_hatype = 0; /* Bad: we have no ARPHRD_UNSPEC */ > sll->sll_halen = 0; I still think this is a mistake. We're papering over so many lies to the compiler. :P If "uaddr" is actually "struct sockaddr_storage", then we should update the callers... and if "struct sockaddr_ll" doesn't have a fixed size trailing array, we should make a new struct that is telling the truth. ;) Perhaps add this to the UAPI: +struct sockaddr_ll_flex { + unsigned short sll_family; + __be16 sll_protocol; + int sll_ifindex; + unsigned short sll_hatype; + unsigned char sll_pkttype; + unsigned char sll_halen; + unsigned char sll_addr[] __counted_by(sll_halen); +}; And update the memcpy(): - DECLARE_SOCKADDR(struct sockaddr_ll *, sll, uaddr); + struct sockaddr_ll_flex * sll = (struct sockaddr_ll_flex *)uaddr; ? -- Kees Cook