From: Mateusz Jurczyk <mjurczyk@google.com>
Date: Wed, 7 Jun 2017 15:50:38 +0200
Subject: [PATCH] netfilter: nfnetlink: Improve input length sanitization in
 nfnetlink_rcv
References: bnc#1060662
Patch-mainline: v4.12.10
Git-commit: f55ce7b024090a51382ccab2730b96e2f7b4e9cf

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@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/netfilter/nfnetlink.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 80f5ecf2c3d7..ff1f4ce6fba4 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -463,8 +463,7 @@ static void nfnetlink_rcv_skb_batch(struct sk_buff *skb, struct nlmsghdr *nlh)
 	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 *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;
 
-- 
2.14.2