This is a note to let you know that I've just added the patch titled
ppp: fix race in ppp device destruction
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: ppp-fix-race-in-ppp-device-destruction.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Thu Nov 16 15:08:14 CET 2017
From: Guillaume Nault g.nault@alphalink.fr Date: Fri, 6 Oct 2017 17:05:49 +0200 Subject: ppp: fix race in ppp device destruction
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); }
Patches currently in stable-queue which might be from g.nault@alphalink.fr are
queue-4.4/ppp-fix-race-in-ppp-device-destruction.patch queue-4.4/l2tp-check-ps-sock-before-running-pppol2tp_session_ioctl.patch