linux-kernel - [PATCH 3.18 076/124] ipv4: provide stronger user input validation in nl_fib

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Date:   Thu, 20 Apr 2017 08:35:51 +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, Alexander Potapenko <glider@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.18 076/124] ipv4: provide stronger user input validation in nl_fib_input()

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

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

From: Eric Dumazet <edumazet@...gle.com>

commit c64c0b3cac4c5b8cb093727d2c19743ea3965c0b upstream.

Alexander reported a KMSAN splat caused by reads of uninitialized
field (tb_id_in) from user provided struct fib_result_nl

It turns out nl_fib_input() sanity tests on user input is a bit
wrong :

User can pretend nlh->nlmsg_len is big enough, but provide
at sendmsg() time a too small buffer.

Reported-by: Alexander Potapenko <glider@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/ipv4/fib_frontend.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -961,7 +961,8 @@ static void nl_fib_input(struct sk_buff
 
 	net = sock_net(skb->sk);
 	nlh = nlmsg_hdr(skb);
-	if (skb->len < NLMSG_HDRLEN || skb->len < nlh->nlmsg_len ||
+	if (skb->len < nlmsg_total_size(sizeof(*frn)) ||
+	    skb->len < nlh->nlmsg_len ||
 	    nlmsg_len(nlh) < sizeof(*frn))
 		return;