linux-kernel - [PATCH 4.9 003/172] decnet: dn_rtmsg: Improve input length sanitization in dnrmg_receive_user

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Date:   Mon,  3 Jul 2017 15:33:03 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mateusz Jurczyk <mjurczyk@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 003/172] decnet: dn_rtmsg: Improve input length sanitization in dnrmg_receive_user_skb

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mateusz Jurczyk <mjurczyk@...gle.com>

[ Upstream commit dd0da17b209ed91f39872766634ca967c170ada1 ]

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 <mjurczyk@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/decnet/netfilter/dn_rtmsg.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/decnet/netfilter/dn_rtmsg.c
+++ b/net/decnet/netfilter/dn_rtmsg.c
@@ -102,7 +102,9 @@ static inline void dnrmg_receive_user_sk
 {
 	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))