Commit f55ce7b0 authored Jun 07, 2017 by Mateusz Jurczyk Committed by Pablo Neira Ayuso Jul 17, 2017

netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

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>

parent 533da29b

net/netfilter/nfnetlink.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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;