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From: Pablo Neira Ayuso <pablo@netfilter.org>
To: netfilter-devel@vger.kernel.org
Cc: davem@davemloft.net, netdev@vger.kernel.org
Subject: [PATCH 1/5] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv
Date: Tue, 18 Jul 2017 12:13:55 +0200
Message-ID: <1500372839-6735-2-git-send-email-pablo@netfilter.org> (raw)
In-Reply-To: <1500372839-6735-1-git-send-email-pablo@netfilter.org>

From: Mateusz Jurczyk <mjurczyk@google.com>

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>
---
 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 92b05e188fd1..733d3e4a30d8 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -472,8 +472,7 @@ 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,
@@ -500,7 +499,8 @@ 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;
 
-- 
2.1.4


  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-18 10:13 [PATCH 0/5] Netfilter fixes for net Pablo Neira Ayuso
2017-07-18 10:13 ` Pablo Neira Ayuso [this message]
2017-07-18 10:13 ` [PATCH 2/5] netfilter: remove old pre-netns era hook api Pablo Neira Ayuso
2017-07-18 10:13 ` [PATCH 3/5] netfilter: nat: fix src map lookup Pablo Neira Ayuso
2017-07-18 10:13 ` [PATCH 4/5] netfilter: nf_tables: only allow in/output for arp packets Pablo Neira Ayuso
2017-07-18 10:13 ` [PATCH 5/5] netfilter: expect: fix crash when putting uninited expectation Pablo Neira Ayuso
2017-07-18 19:03 ` [PATCH 0/5] Netfilter fixes for net David Miller
2017-07-18 21:11   ` Florian Westphal
2017-07-18 21:54     ` David Miller

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