[PATCH 3.16 142/217] ppp: take reference on channels netns

From: Ben Hutchings
Date: Tue Apr 26 2016 - 20:09:24 EST

3.16.35-rc1 review patch. If anyone has any objections, please let me know.

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

From: Guillaume Nault <g.nault@xxxxxxxxxxxx>

commit 1f461dcdd296eecedaffffc6bae2bfa90bd7eb89 upstream.

Let channels hold a reference on their network namespace.
Some channel types, like ppp_async and ppp_synctty, can have their
userspace controller running in a different namespace. Therefore they
can't rely on them to preclude their netns from being removed from
under them.

==================================================================
BUG: KASAN: use-after-free in ppp_unregister_channel+0x372/0x3a0 at
addr ffff880064e217e0
Read of size 8 by task syz-executor/11581
=============================================================================
BUG net_namespace (Not tainted): kasan: bad access detected
-----------------------------------------------------------------------------

Disabling lock debugging due to kernel taint
INFO: Allocated in copy_net_ns+0x6b/0x1a0 age=92569 cpu=3 pid=6906
[< none >] ___slab_alloc+0x4c7/0x500 kernel/mm/slub.c:2440
[< none >] __slab_alloc+0x4c/0x90 kernel/mm/slub.c:2469
[< inline >] slab_alloc_node kernel/mm/slub.c:2532
[< inline >] slab_alloc kernel/mm/slub.c:2574
[< none >] kmem_cache_alloc+0x23a/0x2b0 kernel/mm/slub.c:2579
[< inline >] kmem_cache_zalloc kernel/include/linux/slab.h:597
[< inline >] net_alloc kernel/net/core/net_namespace.c:325
[< none >] copy_net_ns+0x6b/0x1a0 kernel/net/core/net_namespace.c:360
[< none >] create_new_namespaces+0x2f6/0x610 kernel/kernel/nsproxy.c:95
[< none >] copy_namespaces+0x297/0x320 kernel/kernel/nsproxy.c:150
[< none >] copy_process.part.35+0x1bf4/0x5760 kernel/kernel/fork.c:1451
[< inline >] copy_process kernel/kernel/fork.c:1274
[< none >] _do_fork+0x1bc/0xcb0 kernel/kernel/fork.c:1723
[< inline >] SYSC_clone kernel/kernel/fork.c:1832
[< none >] SyS_clone+0x37/0x50 kernel/kernel/fork.c:1826
[< none >] entry_SYSCALL_64_fastpath+0x16/0x7a kernel/arch/x86/entry/entry_64.S:185

INFO: Freed in net_drop_ns+0x67/0x80 age=575 cpu=2 pid=2631
[< none >] __slab_free+0x1fc/0x320 kernel/mm/slub.c:2650
[< inline >] slab_free kernel/mm/slub.c:2805
[< none >] kmem_cache_free+0x2a0/0x330 kernel/mm/slub.c:2814
[< inline >] net_free kernel/net/core/net_namespace.c:341
[< none >] net_drop_ns+0x67/0x80 kernel/net/core/net_namespace.c:348
[< none >] cleanup_net+0x4e5/0x600 kernel/net/core/net_namespace.c:448
[< none >] process_one_work+0x794/0x1440 kernel/kernel/workqueue.c:2036
[< none >] worker_thread+0xdb/0xfc0 kernel/kernel/workqueue.c:2170
[< none >] kthread+0x23f/0x2d0 kernel/drivers/block/aoe/aoecmd.c:1303
[< none >] ret_from_fork+0x3f/0x70 kernel/arch/x86/entry/entry_64.S:468
INFO: Slab 0xffffea0001938800 objects=3 used=0 fp=0xffff880064e20000
flags=0x5fffc0000004080
INFO: Object 0xffff880064e20000 @offset=0 fp=0xffff880064e24200

CPU: 1 PID: 11581 Comm: syz-executor Tainted: G B 4.4.0+
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
00000000ffffffff ffff8800662c7790 ffffffff8292049d ffff88003e36a300
ffff880064e20000 ffff880064e20000 ffff8800662c77c0 ffffffff816f2054
ffff88003e36a300 ffffea0001938800 ffff880064e20000 0000000000000000
Call Trace:
[< inline >] __dump_stack kernel/lib/dump_stack.c:15
[<ffffffff8292049d>] dump_stack+0x6f/0xa2 kernel/lib/dump_stack.c:50
[<ffffffff816f2054>] print_trailer+0xf4/0x150 kernel/mm/slub.c:654
[<ffffffff816f875f>] object_err+0x2f/0x40 kernel/mm/slub.c:661
[< inline >] print_address_description kernel/mm/kasan/report.c:138
[<ffffffff816fb0c5>] kasan_report_error+0x215/0x530 kernel/mm/kasan/report.c:236
[< inline >] kasan_report kernel/mm/kasan/report.c:259
[<ffffffff816fb4de>] __asan_report_load8_noabort+0x3e/0x40 kernel/mm/kasan/report.c:280
[< inline >] ? ppp_pernet kernel/include/linux/compiler.h:218
[<ffffffff83ad71b2>] ? ppp_unregister_channel+0x372/0x3a0 kernel/drivers/net/ppp/ppp_generic.c:2392
[< inline >] ppp_pernet kernel/include/linux/compiler.h:218
[<ffffffff83ad71b2>] ppp_unregister_channel+0x372/0x3a0 kernel/drivers/net/ppp/ppp_generic.c:2392
[< inline >] ? ppp_pernet kernel/drivers/net/ppp/ppp_generic.c:293
[<ffffffff83ad6f26>] ? ppp_unregister_channel+0xe6/0x3a0 kernel/drivers/net/ppp/ppp_generic.c:2392
[<ffffffff83ae18f3>] ppp_asynctty_close+0xa3/0x130 kernel/drivers/net/ppp/ppp_async.c:241
[<ffffffff83ae1850>] ? async_lcp_peek+0x5b0/0x5b0 kernel/drivers/net/ppp/ppp_async.c:1000
[<ffffffff82c33239>] tty_ldisc_close.isra.1+0x99/0xe0 kernel/drivers/tty/tty_ldisc.c:478
[<ffffffff82c332c0>] tty_ldisc_kill+0x40/0x170 kernel/drivers/tty/tty_ldisc.c:744
[<ffffffff82c34943>] tty_ldisc_release+0x1b3/0x260 kernel/drivers/tty/tty_ldisc.c:772
[<ffffffff82c1ef21>] tty_release+0xac1/0x13e0 kernel/drivers/tty/tty_io.c:1901
[<ffffffff82c1e460>] ? release_tty+0x320/0x320 kernel/drivers/tty/tty_io.c:1688
[<ffffffff8174de36>] __fput+0x236/0x780 kernel/fs/file_table.c:208
[<ffffffff8174e405>] ____fput+0x15/0x20 kernel/fs/file_table.c:244
[<ffffffff813595ab>] task_work_run+0x16b/0x200 kernel/kernel/task_work.c:115
[< inline >] exit_task_work kernel/include/linux/task_work.h:21
[<ffffffff81307105>] do_exit+0x8b5/0x2c60 kernel/kernel/exit.c:750
[<ffffffff813fdd20>] ? debug_check_no_locks_freed+0x290/0x290 kernel/kernel/locking/lockdep.c:4123
[<ffffffff81306850>] ? mm_update_next_owner+0x6f0/0x6f0 kernel/kernel/exit.c:357
[<ffffffff813215e6>] ? __dequeue_signal+0x136/0x470 kernel/kernel/signal.c:550
[<ffffffff8132067b>] ? recalc_sigpending_tsk+0x13b/0x180 kernel/kernel/signal.c:145
[<ffffffff81309628>] do_group_exit+0x108/0x330 kernel/kernel/exit.c:880
[<ffffffff8132b9d4>] get_signal+0x5e4/0x14f0 kernel/kernel/signal.c:2307
[< inline >] ? kretprobe_table_lock kernel/kernel/kprobes.c:1113
[<ffffffff8151d355>] ? kprobe_flush_task+0xb5/0x450 kernel/kernel/kprobes.c:1158
[<ffffffff8115f7d3>] do_signal+0x83/0x1c90 kernel/arch/x86/kernel/signal.c:712
[<ffffffff8151d2a0>] ? recycle_rp_inst+0x310/0x310 kernel/include/linux/list.h:655
[<ffffffff8115f750>] ? setup_sigcontext+0x780/0x780 kernel/arch/x86/kernel/signal.c:165
[<ffffffff81380864>] ? finish_task_switch+0x424/0x5f0 kernel/kernel/sched/core.c:2692
[< inline >] ? finish_lock_switch kernel/kernel/sched/sched.h:1099
[<ffffffff81380560>] ? finish_task_switch+0x120/0x5f0 kernel/kernel/sched/core.c:2678
[< inline >] ? context_switch kernel/kernel/sched/core.c:2807
[<ffffffff85d794e9>] ? __schedule+0x919/0x1bd0 kernel/kernel/sched/core.c:3283
[<ffffffff81003901>] exit_to_usermode_loop+0xf1/0x1a0 kernel/arch/x86/entry/common.c:247
[< inline >] prepare_exit_to_usermode kernel/arch/x86/entry/common.c:282
[<ffffffff810062ef>] syscall_return_slowpath+0x19f/0x210 kernel/arch/x86/entry/common.c:344
[<ffffffff85d88022>] int_ret_from_sys_call+0x25/0x9f kernel/arch/x86/entry/entry_64.S:281
Memory state around the buggy address:
ffff880064e21680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff880064e21700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff880064e21780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff880064e21800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff880064e21880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Fixes: 273ec51dd7ce ("net: ppp_generic - introduce net-namespace functionality v2")
Reported-by: Baozeng Ding <sploving1@xxxxxxxxx>
Signed-off-by: Guillaume Nault <g.nault@xxxxxxxxxxxx>
Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
drivers/net/ppp/ppp_generic.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -2241,7 +2241,7 @@ int ppp_register_net_channel(struct net

pch->ppp = NULL;
pch->chan = chan;
- pch->chan_net = net;
+ pch->chan_net = get_net(net);
chan->ppp = pch;
init_ppp_file(&pch->file, CHANNEL);
pch->file.hdrlen = chan->hdrlen;
@@ -2338,6 +2338,8 @@ 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);