Patch "l2tp: do not accept arbitrary sockets" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

l2tp: do not accept arbitrary sockets

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
l2tp-do-not-accept-arbitrary-sockets.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Tue, 6 Mar 2018 07:54:53 -0800
Subject: l2tp: do not accept arbitrary sockets

From: Eric Dumazet <[email protected]>

[ Upstream commit 17cfe79a65f98abe535261856c5aef14f306dff7 ]

syzkaller found an issue caused by lack of sufficient checks in l2tp_tunnel_create()

RAW sockets can not be considered as UDP ones for instance.

In another patch, we shall replace all pr_err() by less intrusive pr_debug() so that syzkaller can find other bugs faster.

==================================================================

BUG: KASAN: slab-out-of-bounds in setup_udp_tunnel_sock+0x3ee/0x5f0 net/ipv4/udp_tunnel.c:69
dst_release: dst:00000000d53d0d0f refcnt:-1
Write of size 1 at addr ffff8801d013b798 by task syz-executor3/6242

CPU: 1 PID: 6242 Comm: syz-executor3 Not tainted 4.16.0-rc2+ #253
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:412
 __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:435
 setup_udp_tunnel_sock+0x3ee/0x5f0 net/ipv4/udp_tunnel.c:69
 l2tp_tunnel_create+0x1354/0x17f0 net/l2tp/l2tp_core.c:1596
 pppol2tp_connect+0x14b1/0x1dd0 net/l2tp/l2tp_ppp.c:707
 SYSC_connect+0x213/0x4a0 net/socket.c:1640
 SyS_connect+0x24/0x30 net/socket.c:1621
 do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

---
 net/l2tp/l2tp_core.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

@@ -1466,9 +1466,14 @@ int l2tp_tunnel_create(struct net *net,
 		encap = cfg->encap;
 
 	/* Quick sanity checks */
+	err = -EPROTONOSUPPORT;
+	if (sk->sk_type != SOCK_DGRAM) {
+		pr_debug("tunl %hu: fd %d wrong socket type\n",
+			 tunnel_id, fd);
+		goto err;
+	}
 	switch (encap) {
 	case L2TP_ENCAPTYPE_UDP:
-		err = -EPROTONOSUPPORT;
 		if (sk->sk_protocol != IPPROTO_UDP) {
 			pr_err("tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
 			       tunnel_id, fd, sk->sk_protocol, IPPROTO_UDP);

@@ -1476,7 +1481,6 @@ int l2tp_tunnel_create(struct net *net,
 		}
 		break;
 	case L2TP_ENCAPTYPE_IP:
-		err = -EPROTONOSUPPORT;
 		if (sk->sk_protocol != IPPROTO_L2TP) {
 			pr_err("tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
 			       tunnel_id, fd, sk->sk_protocol, IPPROTO_L2TP);

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/ipv6-fix-access-to-non-linear-packet-in-ndisc_fill_redirect_hdr_option.patch queue-4.15/skbuff-fix-not-waking-applications-when-errors-are-enqueued.patch queue-4.15/l2tp-do-not-accept-arbitrary-sockets.patch queue-4.15/tcp-purge-write-queue-upon-aborting-the-connection.patch queue-4.15/net-use-skb_to_full_sk-in-skb_update_prio.patch queue-4.15/ieee802154-6lowpan-fix-possible-null-deref-in-lowpan_device_event.patch