[PATCH 4.12 80/99] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

Greg Kroah-Hartman
2017-08-28T09:01:11Z

From: Mateusz Jurczyk <mjurczyk@google.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@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>

---
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;