[PATCH 3.18 41/49] ppp: defer netns reference release for ppp channel

From	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Newsgroups	linux.kernel
Subject	[PATCH 3.18 41/49] ppp: defer netns reference release for ppp channel
Date	2017-05-18 15:20 +0200
Message-ID	<tItvs-33n-47@gated-at.bofh.it> (permalink)
References	<tItvr-33n-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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

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

From: WANG Cong <xiyou.wangcong@gmail.com>

commit 205e1e255c479f3fd77446415706463b282f94e4 upstream.

Matt reported that we have a NULL pointer dereference
in ppp_pernet() from ppp_connect_channel(),
i.e. pch->chan_net is NULL.

This is due to that a parallel ppp_unregister_channel()
could happen while we are in ppp_connect_channel(), during
which pch->chan_net set to NULL. Since we need a reference
to net per channel, it makes sense to sync the refcnt
with the life time of the channel, therefore we should
release this reference when we destroy it.

Fixes: 1f461dcdd296 ("ppp: take reference on channels netns")
Reported-by: Matt Bennett <Matt.Bennett@alliedtelesis.co.nz>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linux-ppp@vger.kernel.org
Cc: Guillaume Nault <g.nault@alphalink.fr>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/net/ppp/ppp_generic.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -2342,8 +2342,6 @@ ppp_unregister_channel(struct ppp_channe
 	spin_lock_bh(&pn->all_channels_lock);
 	list_del(&pch->list);
 	spin_unlock_bh(&pn->all_channels_lock);
-	put_net(pch->chan_net);
-	pch->chan_net = NULL;
 
 	pch->file.dead = 1;
 	wake_up_interruptible(&pch->file.rwait);
@@ -2960,6 +2958,9 @@ ppp_disconnect_channel(struct channel *p
  */
 static void ppp_destroy_channel(struct channel *pch)
 {
+	put_net(pch->chan_net);
+	pch->chan_net = NULL;
+
 	atomic_dec(&channel_count);
 
 	if (!pch->file.dead) {

Thread

[PATCH 3.18 00/49] 3.18.54-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 22/49] SMB3: Work around mount failure when using SMB3 dialect to Macs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 01/49] target/fileio: Fix zero-length READ and WRITE handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 41/49] ppp: defer netns reference release for ppp channel Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 09/49] staging: comedi: jr3_pci: cope with jiffies wraparound Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 31/49] perf: Fix event->ctx locking Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 11/49] usb: hub: Do not attempt to autosuspend disconnected devices Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 07/49] staging: gdm724x: gdm_mux: fix use-after-free on module unload Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 44/49] sched: panic on corrupted stack end Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 06/49] staging: vt6656: use off stack for out buffer USB transfers. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:20 +0200
  [PATCH 3.18 08/49] staging: comedi: jr3_pci: fix possible null pointer dereference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 32/49] arm64: perf: reject groups spanning multiple HW PMUs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 42/49] HID: core: prevent out-of-bound readings Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 05/49] staging: vt6656: use off stack for in buffer USB transfers. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 04/49] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 17/49] IB/mlx4: Fix ib device initialization error flow Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 39/49] ipv6: sctp: fix lockdep splat in sctp_v6_get_dst() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 33/49] perf: Fix race in swevent hash Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 26/49] md/raid1: avoid reusing a resync bio after error handling. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 38/49] ipv6: sctp: add rcu protection around np->opt Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 29/49] Bluetooth: Fix user channel for 32bit userspace on 64bit kernel Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 37/49] sg: Fix double-free when drives detach during SG_IO Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 36/49] ext4: fix potential use after free in __ext4_journal_stop Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 18/49] fs/xattr.c: zero out memory copied to userspace in getxattr Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 03/49] USB: serial: ftdi_sio: add device ID for Microsemi/Arrow SF2PLUS Dev Kit Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 34/49] ASN.1: Fix non-match detection failure on data overrun Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 21/49] Set unicode flag on cifs echo request to avoid Mac error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 45/49] ALSA: seq: Fix race at timer setup and close Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 30/49] arm64: make sys_call_table const Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 25/49] padata: free correct variable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 28/49] serial: omap: suspend device on probe errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 40/49] af_unix: Guard against other == sk in unix_dgram_sendmsg Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:30 +0200
  [PATCH 3.18 02/49] usb: host: xhci: print correct command ring address Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:40 +0200
  [PATCH 3.18 12/49] usb: misc: legousbtower: Fix buffers on stack Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:40 +0200
  [PATCH 3.18 20/49] fs/block_dev: always invalidate cleancache in invalidate_bdev() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:40 +0200
  [PATCH 3.18 16/49] IB/IPoIB: ibX: failed to create mcg debug file Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:40 +0200
  [PATCH 3.18 14/49] um: Fix PTRACE_POKEUSER on x86_64 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 15:40 +0200
  Re: [PATCH 3.18 00/49] 3.18.54-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-05-18 19:30 +0200
  Re: [PATCH 3.18 00/49] 3.18.54-stable review Guenter Roeck <linux@roeck-us.net> - 2017-05-19 03:10 +0200

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