netdev - [PATCH v2 net] l2tp: do not use udp

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Date:   Thu, 09 Feb 2017 16:15:52 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v2 net] l2tp: do not use udp_ioctl()

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

udp_ioctl(), as its name suggests, is used by UDP protocols,
but is also used by L2TP :(

L2TP should use its own handler, because it really does not
look the same.

SIOCINQ for instance should not assume UDP checksum or headers.

Thanks to Andrey and syzkaller team for providing the report
and a nice reproducer.

While crashes only happen on recent kernels (after commit 
7c13f97ffde6 ("udp: do fwd memory scheduling on dequeue")), this
probably needs to be backported to older kernels.

Fixes: 7c13f97ffde6 ("udp: do fwd memory scheduling on dequeue")
Fixes: 85584672012e ("udp: Fix udp_poll() and ioctl()")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
Acked-by: Paolo Abeni <pabeni@...hat.com>
---
v2: Adding the EXPORT_SYMBOL(l2tp_ioctl) for ipv6, of course...

 net/l2tp/l2tp_core.h |    1 +
 net/l2tp/l2tp_ip.c   |   27 ++++++++++++++++++++++++++-
 net/l2tp/l2tp_ip6.c  |    2 +-
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 8f560f7140a05694c13904d9b171ba67d9d11292..aebf281d09eeb31c531eb624bd2ddd78cab8da9b 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -263,6 +263,7 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb,
 int l2tp_nl_register_ops(enum l2tp_pwtype pw_type,
 			 const struct l2tp_nl_cmd_ops *ops);
 void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type);
+int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg);
 
 /* Session reference counts. Incremented when code obtains a reference
  * to a session.
diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 3d73278b86ca34bfbd774dc8f52e490169445e1b..28c21546d5b60dcd07bbf6347389e97c918bf40f 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -11,6 +11,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <asm/ioctls.h>
 #include <linux/icmp.h>
 #include <linux/module.h>
 #include <linux/skbuff.h>
@@ -553,6 +554,30 @@ static int l2tp_ip_recvmsg(struct sock *sk, struct msghdr *msg,
 	return err ? err : copied;
 }
 
+int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg)
+{
+	struct sk_buff *skb;
+	int amount;
+
+	switch (cmd) {
+	case SIOCOUTQ:
+		amount = sk_wmem_alloc_get(sk);
+		break;
+	case SIOCINQ:
+		spin_lock_bh(&sk->sk_receive_queue.lock);
+		skb = skb_peek(&sk->sk_receive_queue);
+		amount = skb ? skb->len : 0;
+		spin_unlock_bh(&sk->sk_receive_queue.lock);
+		break;
+
+	default:
+		return -ENOIOCTLCMD;
+	}
+
+	return put_user(amount, (int __user *)arg);
+}
+EXPORT_SYMBOL(l2tp_ioctl);
+
 static struct proto l2tp_ip_prot = {
 	.name		   = "L2TP/IP",
 	.owner		   = THIS_MODULE,
@@ -561,7 +586,7 @@ static struct proto l2tp_ip_prot = {
 	.bind		   = l2tp_ip_bind,
 	.connect	   = l2tp_ip_connect,
 	.disconnect	   = l2tp_ip_disconnect,
-	.ioctl		   = udp_ioctl,
+	.ioctl		   = l2tp_ioctl,
 	.destroy	   = l2tp_ip_destroy_sock,
 	.setsockopt	   = ip_setsockopt,
 	.getsockopt	   = ip_getsockopt,
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index 331ccf5a7bad80e011997e071489d7775b0c68c6..f47c45250f86c9189e0a6bbfd92b21cbe2069406 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -722,7 +722,7 @@ static struct proto l2tp_ip6_prot = {
 	.bind		   = l2tp_ip6_bind,
 	.connect	   = l2tp_ip6_connect,
 	.disconnect	   = l2tp_ip6_disconnect,
-	.ioctl		   = udp_ioctl,
+	.ioctl		   = l2tp_ioctl,
 	.destroy	   = l2tp_ip6_destroy_sock,
 	.setsockopt	   = ipv6_setsockopt,
 	.getsockopt	   = ipv6_getsockopt,