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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Beniamino Galvani <bgalvani@redhat.com>,
	Guillaume Nault <g.nault@alphalink.fr>,
	"David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.4 18/28] ppp: fix race in ppp device destruction
Date: Thu, 16 Nov 2017 18:42:36 +0100
Message-ID: <20171116174139.588838135@linuxfoundation.org> (raw)
In-Reply-To: <20171116174138.714641106@linuxfoundation.org>

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

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

From: Guillaume Nault <g.nault@alphalink.fr>


[ Upstream commit 6151b8b37b119e8e3a8401b080d532520c95faf4 ]

ppp_release() tries to ensure that netdevices are unregistered before
decrementing the unit refcount and running ppp_destroy_interface().

This is all fine as long as the the device is unregistered by
ppp_release(): the unregister_netdevice() call, followed by
rtnl_unlock(), guarantee that the unregistration process completes
before rtnl_unlock() returns.

However, the device may be unregistered by other means (like
ppp_nl_dellink()). If this happens right before ppp_release() calling
rtnl_lock(), then ppp_release() has to wait for the concurrent
unregistration code to release the lock.
But rtnl_unlock() releases the lock before completing the device
unregistration process. This allows ppp_release() to proceed and
eventually call ppp_destroy_interface() before the unregistration
process completes. Calling free_netdev() on this partially unregistered
device will BUG():

 ------------[ cut here ]------------
 kernel BUG at net/core/dev.c:8141!
 invalid opcode: 0000 [#1] SMP

 CPU: 1 PID: 1557 Comm: pppd Not tainted 4.14.0-rc2+ #4
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1.fc26 04/01/2014

 Call Trace:
  ppp_destroy_interface+0xd8/0xe0 [ppp_generic]
  ppp_disconnect_channel+0xda/0x110 [ppp_generic]
  ppp_unregister_channel+0x5e/0x110 [ppp_generic]
  pppox_unbind_sock+0x23/0x30 [pppox]
  pppoe_connect+0x130/0x440 [pppoe]
  SYSC_connect+0x98/0x110
  ? do_fcntl+0x2c0/0x5d0
  SyS_connect+0xe/0x10
  entry_SYSCALL_64_fastpath+0x1a/0xa5

 RIP: free_netdev+0x107/0x110 RSP: ffffc28a40573d88
 ---[ end trace ed294ff0cc40eeff ]---

We could set the ->needs_free_netdev flag on PPP devices and move the
ppp_destroy_interface() logic in the ->priv_destructor() callback. But
that'd be quite intrusive as we'd first need to unlink from the other
channels and units that depend on the device (the ones that used the
PPPIOCCONNECT and PPPIOCATTACH ioctls).

Instead, we can just let the netdevice hold a reference on its
ppp_file. This reference is dropped in ->priv_destructor(), at the very
end of the unregistration process, so that neither ppp_release() nor
ppp_disconnect_channel() can call ppp_destroy_interface() in the interim.

Reported-by: Beniamino Galvani <bgalvani@redhat.com>
Fixes: 8cb775bc0a34 ("ppp: fix device unregistration upon netns deletion")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ppp/ppp_generic.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -1110,7 +1110,17 @@ ppp_get_stats64(struct net_device *dev,
 static struct lock_class_key ppp_tx_busylock;
 static int ppp_dev_init(struct net_device *dev)
 {
+	struct ppp *ppp;
+
 	dev->qdisc_tx_busylock = &ppp_tx_busylock;
+
+	ppp = netdev_priv(dev);
+	/* Let the netdevice take a reference on the ppp file. This ensures
+	 * that ppp_destroy_interface() won't run before the device gets
+	 * unregistered.
+	 */
+	atomic_inc(&ppp->file.refcnt);
+
 	return 0;
 }
 
@@ -1133,6 +1143,15 @@ static void ppp_dev_uninit(struct net_de
 	wake_up_interruptible(&ppp->file.rwait);
 }
 
+static void ppp_dev_priv_destructor(struct net_device *dev)
+{
+	struct ppp *ppp;
+
+	ppp = netdev_priv(dev);
+	if (atomic_dec_and_test(&ppp->file.refcnt))
+		ppp_destroy_interface(ppp);
+}
+
 static const struct net_device_ops ppp_netdev_ops = {
 	.ndo_init	 = ppp_dev_init,
 	.ndo_uninit      = ppp_dev_uninit,
@@ -1150,6 +1169,7 @@ static void ppp_setup(struct net_device
 	dev->tx_queue_len = 3;
 	dev->type = ARPHRD_PPP;
 	dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
+	dev->destructor = ppp_dev_priv_destructor;
 	netif_keep_dst(dev);
 }
 

  parent reply index

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-16 17:42 [PATCH 4.4 00/28] 4.4.99-stable review Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 01/28] mac80211: accept key reinstall without changing anything Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 02/28] mac80211: use constant time comparison with keys Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 03/28] mac80211: dont compare TKIP TX MIC key in reinstall prevention Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 04/28] usb: usbtest: fix NULL pointer dereference Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 05/28] Input: ims-psu - check if CDC union descriptor is sane Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 06/28] ALSA: seq: Cancel pending autoload work at unbinding device Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 07/28] tun/tap: sanitize TUNSETSNDBUF input Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 08/28] tcp: fix tcp_mtu_probe() vs highest_sack Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 09/28] l2tp: check ps->sock before running pppol2tp_session_ioctl() Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 10/28] tun: call dev_get_valid_name() before register_netdevice() Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 11/28] sctp: add the missing sock_owned_by_user check in sctp_icmp_redirect Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 12/28] packet: avoid panic in packet_getsockopt() Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 13/28] ipv6: flowlabel: do not leave opt->tot_len with garbage Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 14/28] net/unix: dont show information about sockets from other namespaces Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 15/28] ip6_gre: only increase err_count for some certain type icmpv6 in ip6gre_err Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 16/28] tun: allow positive return values on dev_get_valid_name() call Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 17/28] sctp: reset owner sk for data chunks on out queues when migrating a sock Greg Kroah-Hartman
2017-11-16 17:42 ` Greg Kroah-Hartman [this message]
2017-11-16 17:42 ` [PATCH 4.4 19/28] ipip: only increase err_count for some certain type icmp in ipip_err Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 20/28] tcp/dccp: fix ireq->opt races Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 21/28] tcp/dccp: fix lockdep splat in inet_csk_route_req() Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 23/28] security/keys: add CONFIG_KEYS_COMPAT to Kconfig Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 24/28] tipc: fix link attribute propagation bug Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 25/28] brcmfmac: remove setting IBSS mode when stopping AP Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 26/28] target/iscsi: Fix iSCSI task reassignment handling Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 27/28] target: Fix node_acl demo-mode + uncached dynamic shutdown regression Greg Kroah-Hartman
2017-11-16 17:42 ` [PATCH 4.4 28/28] misc: panel: properly restore atomic counter on error path Greg Kroah-Hartman
2017-11-16 22:44 ` [PATCH 4.4 00/28] 4.4.99-stable review Shuah Khan
2017-11-17  2:01 ` Guenter Roeck
2017-11-17  8:16 ` natechancellor
2017-11-17  8:26   ` Naresh Kamboju
2017-11-17  8:44     ` Greg Kroah-Hartman
2017-11-17  8:30   ` Greg Kroah-Hartman

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