From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751659AbdFGNuo (ORCPT ); Wed, 7 Jun 2017 09:50:44 -0400 Received: from mail-wm0-f45.google.com ([74.125.82.45]:36363 "EHLO mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751528AbdFGNum (ORCPT ); Wed, 7 Jun 2017 09:50:42 -0400 From: Mateusz Jurczyk To: Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal Cc: "David S. Miller" , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv Date: Wed, 7 Jun 2017 15:50:38 +0200 Message-Id: <20170607135038.1592-1-mjurczyk@google.com> X-Mailer: git-send-email 2.13.1.508.gb3defc5cc-goog In-Reply-To: <1496841821.736.35.camel@edumazet-glaptop3.roam.corp.google.com> References: <1496841821.736.35.camel@edumazet-glaptop3.roam.corp.google.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Verify that the length of the socket buffer is sufficient to cover the nlmsghdr structure before accessing the nlh->nlmsg_len field for further input sanitization. If the client only supplies 1-3 bytes of data in sk_buff, then nlh->nlmsg_len remains partially uninitialized and contains leftover memory from the corresponding kernel allocation. Operating on such data may result in indeterminate evaluation of the nlmsg_len < NLMSG_HDRLEN expression. The bug was discovered by a runtime instrumentation designed to detect use of uninitialized memory in the kernel. The patch prevents this and other similar tools (e.g. KMSAN) from flagging this behavior in the future. Signed-off-by: Mateusz Jurczyk --- Changes in v2: - Compare skb->len against NLMSG_HDRLEN to avoid assuming the layout of the nlmsghdr structure. net/netfilter/nfnetlink.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c index 80f5ecf2c3d7..1f9667f52be5 100644 --- a/net/netfilter/nfnetlink.c +++ b/net/netfilter/nfnetlink.c @@ -491,7 +491,8 @@ static void nfnetlink_rcv(struct sk_buff *skb) { struct nlmsghdr *nlh = nlmsg_hdr(skb); - if (nlh->nlmsg_len < NLMSG_HDRLEN || + if (skb->len < NLMSG_HDRLEN || + nlh->nlmsg_len < NLMSG_HDRLEN || skb->len < nlh->nlmsg_len) return; -- 2.13.1.508.gb3defc5cc-goog