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    Subject[PATCH 4.2.y-ckt 158/218] ppp: take reference on channels netns
    Date
    4.2.8-ckt7 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

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

    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@gmail.com>
    Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
    Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/net/ppp/ppp_generic.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
    index e82b43c..6fc526b 100644
    --- a/drivers/net/ppp/ppp_generic.c
    +++ b/drivers/net/ppp/ppp_generic.c
    @@ -2277,7 +2277,7 @@ int ppp_register_net_channel(struct net *net, struct ppp_channel *chan)

    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;
    @@ -2374,6 +2374,8 @@ ppp_unregister_channel(struct ppp_channel *chan)
    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);
    --
    2.7.4
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