linux-kernel - [PATCH 4.12 80/99] netfilter: nfnetlink: Improve input length sanitization in nfnetlink

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Date:   Mon, 28 Aug 2017 10:05:18 +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>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>
Subject: [PATCH 4.12 80/99] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

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

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

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

commit f55ce7b024090a51382ccab2730b96e2f7b4e9cf upstream.

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 <mjurczyk@...gle.com>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Cc: Florian Westphal <fw@...len.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/netfilter/nfnetlink.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -463,8 +463,7 @@ static void nfnetlink_rcv_skb_batch(stru
 	if (msglen > skb->len)
 		msglen = skb->len;

-	if (nlh->nlmsg_len < NLMSG_HDRLEN ||
-	    skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
+	if (skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
 		return;

 	err = nla_parse(cda, NFNL_BATCH_MAX, attr, attrlen, nfnl_batch_policy,
@@ -491,7 +490,8 @@ static void nfnetlink_rcv(struct sk_buff
 {
 	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;