From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751504AbdFGOOf (ORCPT ); Wed, 7 Jun 2017 10:14:35 -0400 Received: from mail-wr0-f181.google.com ([209.85.128.181]:32850 "EHLO mail-wr0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751207AbdFGOOd (ORCPT ); Wed, 7 Jun 2017 10:14:33 -0400 From: Mateusz Jurczyk To: Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal Cc: "David S. Miller" , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, linux-decnet-user@lists.sourceforge.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] decnet: dn_rtmsg: Improve input length sanitization in dnrmg_receive_user_skb Date: Wed, 7 Jun 2017 16:14:29 +0200 Message-Id: <20170607141429.5781-1-mjurczyk@google.com> X-Mailer: git-send-email 2.13.1.508.gb3defc5cc-goog In-Reply-To: <20170607131429.30441-1-mjurczyk@google.com> References: <20170607131429.30441-1-mjurczyk@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 < sizeof(*nlh) 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 sizeof(*nlh) instead of sizeof(nlh->nlmsg_len) to avoid assuming the layout of the nlmsghdr structure. This was motivated by Eric Dumazet's comment on a related patch submission. net/decnet/netfilter/dn_rtmsg.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/decnet/netfilter/dn_rtmsg.c b/net/decnet/netfilter/dn_rtmsg.c index 1ed81ac6dd1a..aa8ffecc46a4 100644 --- a/net/decnet/netfilter/dn_rtmsg.c +++ b/net/decnet/netfilter/dn_rtmsg.c @@ -102,7 +102,9 @@ static inline void dnrmg_receive_user_skb(struct sk_buff *skb) { struct nlmsghdr *nlh = nlmsg_hdr(skb); - if (nlh->nlmsg_len < sizeof(*nlh) || skb->len < nlh->nlmsg_len) + if (skb->len < sizeof(*nlh) || + nlh->nlmsg_len < sizeof(*nlh) || + skb->len < nlh->nlmsg_len) return; if (!netlink_capable(skb, CAP_NET_ADMIN)) -- 2.13.1.508.gb3defc5cc-goog