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Date:   Sat, 12 Jan 2019 08:31:05 +0900
From:   zzoru <zzoru007@...il.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        Andrey Vagin <avagin@...tuozzo.com>,
        "dsahern@...il.com" <dsahern@...il.com>,
        "nicolas.dichtel@...nd.com" <nicolas.dichtel@...nd.com>,
        "tyhicks@...onical.com" <tyhicks@...onical.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "syzkaller@...glegroups.com" <syzkaller@...glegroups.com>
Subject: Re: net/core: BUG in copy_net_ns()

> I received 3 spam messages from this address today.
> We can simply ignore this report.
I already mentioned about this.

> and, sorry for my encrypted mails.
> I don't understand this failure report at all.
>
> I don't see the connection to copy_net_ns().  And I don't see how the
> suggested patch short of covering up a memory stomp could possibly make
> a difference.
>
> What am I missing?
> void execute_one(void)
> {
>   syscall(__NR_unshare, 0x40000000);
> }
ksys_unshare -> unshare_nsproxy_namespaces -> create_new_namespaces ->
copy_net_ns
unshare(CLONE_NEWNET) calls copy_net_ns() (It requires the CAP_SYS_ADMIN
capability)

I made many error reports about this bug, and the other one is

[   90.289025] WARNING: CPU: 1 PID: 1732 at mm/page_alloc.c:4415
__alloc_pages_slowpath+0x1cb1/0x2220
[   90.290223] Modules linked in:
[   90.290639] CPU: 1 PID: 1732 Comm: kworker/u4:5 Not tainted 5.0.0-rc1+ #6
[   90.291475] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[   90.292681] Workqueue: writeback wb_workfn (flush-8:0)
[   90.293350] RIP: 0010:__alloc_pages_slowpath+0x1cb1/0x2220
[   90.294075] Code: 8b 84 24 a8 00 00 00 e9 ea f1 ff ff 85 d2 0f 85 0b
01 00 00 48 c7 c7 c0 5e 55 84 e8 79 f8 23 02 e9 86 f9 ff ff 44 8b 74 24
0c <0f> 0b 48 b8 00 00 00 00 00 fc ff df 48 8b 54 24 18 48 c1 ea 03 80
[   90.296527] RSP: 0018:ffff888064276dd8 EFLAGS: 00010046
[   90.297203] RAX: 0000000000000000 RBX: 0000000000000000 RCX:
1ffff1100c84eda8
[   90.297784] kmemleak: Cannot allocate a kmemleak_object structure
[   90.298186] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
ffff88807ffdd528
[   90.298242] RBP: dffffc0000000000 R08: 0000000000000000 R09:
0000000000000679
[   90.298247] R10: 0000000000000000 R11: ffff88807ffdc487 R12:
0000000000000000
[   90.298251] R13: ffff888064277030 R14: 0000000000415a00 R15:
ffff888064277030
[   90.298257] FS:  0000000000000000(0000) GS:ffff88806d500000(0000)
knlGS:0000000000000000
[   90.298262] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   90.298267] CR2: 00007fff6ac6a718 CR3: 0000000056578000 CR4:
00000000000006e0
[   90.298272] Call Trace:
[   90.298283]  ? __alloc_pages_slowpath+0x1ce6/0x2220
[   90.298299]  ? warn_alloc+0x120/0x120
[   90.302432] kmemleak: Kernel memory leak detector disabled
[   90.303346]  ? lock_acquire+0x103/0x2e0
[   90.303358]  ? __isolate_free_page+0x4b0/0x4b0
[   90.303366]  ? __lock_is_held+0xad/0x140
[   90.303377]  __alloc_pages_nodemask+0x521/0x5f0
[   90.303386]  ? __alloc_pages_slowpath+0x2220/0x2220
[   90.315010]  cache_grow_begin+0x95/0x300
[   90.315613]  fallback_alloc+0x1ce/0x270
[   90.316211]  ? mempool_free+0x360/0x360
[   90.316767]  kmem_cache_alloc+0x286/0x2f0
[   90.317348]  ? mempool_free+0x360/0x360
[   90.317919]  create_object+0x83/0x880
[   90.318517]  ? kmemleak_disable+0x90/0x90
[   90.319103]  ? mark_held_locks+0xc1/0x140
[   90.319679]  ? kmem_cache_alloc+0x9c/0x2f0
[   90.320307]  ? mempool_free+0x360/0x360
[   90.320900]  kmem_cache_alloc+0x18f/0x2f0
[   90.321650]  ? mempool_free+0x360/0x360
[   90.322228]  mempool_alloc+0x13e/0x340
[   90.322765]  ? mempool_destroy+0x30/0x30
[   90.323370]  ? mark_held_locks+0xc1/0x140
[   90.323993]  ? _raw_spin_unlock_irqrestore+0x3e/0x50
[   90.324786]  bio_alloc_bioset+0x36f/0x5d0
[   90.325397]  ? __test_set_page_writeback+0x136/0x960
[   90.326161]  ? bvec_alloc+0x2d0/0x2d0
[   90.326708]  ? wait_for_stable_page+0x290/0x290
[   90.327392]  submit_bh_wbc.isra.57+0x128/0x680
[   90.328053]  ? create_page_buffers+0x111/0x200
[   90.328685]  __block_write_full_page+0x6e8/0xcd0
[   90.329339]  ? check_disk_change+0x130/0x130
[   90.329966]  block_write_full_page+0x202/0x250
[   90.330675]  ? check_disk_change+0x130/0x130
[   90.331291]  __writepage+0x62/0xe0
[   90.331786]  write_cache_pages+0x5b8/0xf60
[   90.332375]  ? __wb_calc_thresh+0x290/0x290
[   90.332976]  ? clear_page_dirty_for_io+0x5c0/0x5c0
[   90.333686]  ? mark_held_locks+0x140/0x140
[   90.334301]  ? print_circular_bug_entry+0x1f/0x60
[   90.334999]  ? __lock_acquire+0x5d6/0x4630
[   90.335621]  generic_writepages+0xda/0x150
[   90.336243]  ? write_cache_pages+0xf60/0xf60
[   90.336852]  ? mark_held_locks+0x140/0x140
[   90.337453]  ? blkdev_readpages+0x30/0x30
[   90.338020]  do_writepages+0xf0/0x290
[   90.338611]  ? page_writeback_cpu_online+0x10/0x10
[   90.339324]  ? __lock_is_held+0xad/0x140
[   90.339900]  __writeback_single_inode+0xf3/0x1000
[   90.340587]  writeback_sb_inodes+0x4e7/0xce0
[   90.341214]  ? __writeback_single_inode+0x1000/0x1000
[   90.341929]  ? down_read_trylock+0x5b/0x90
[   90.342579]  ? trylock_super+0x1d/0x100
[   90.343162]  __writeback_inodes_wb+0x109/0x220
[   90.343799]  wb_writeback+0x7a1/0xb90
[   90.344347]  ? writeback_inodes_wb.constprop.44+0x190/0x190
[   90.345143]  ? cpumask_next+0x1f/0x30
[   90.345679]  ? find_next_bit+0x101/0x130
[   90.346281]  ? get_nr_dirty_inodes+0xd0/0x130
[   90.346909]  wb_workfn+0x921/0xec0
[   90.347397]  ? process_one_work+0xadd/0x1bb0
[   90.348025]  ? inode_wait_for_writeback+0x30/0x30
[   90.348700]  process_one_work+0xbbd/0x1bb0
[   90.349314]  ? max_active_store+0x130/0x130
[   90.349915]  ? do_raw_spin_lock+0x11b/0x280
[   90.350557]  worker_thread+0x8c/0x1060
[   90.351096]  ? __kthread_parkme+0xf8/0x1a0
[   90.351673]  ? process_one_work+0x1bb0/0x1bb0
[   90.352334]  kthread+0x347/0x410
[   90.352798]  ? kthread_create_worker_on_cpu+0xe0/0xe0
[   90.353509]  ret_from_fork+0x3a/0x50
[   90.354020] irq event stamp: 282384
[   90.354590] hardirqs last  enabled at (282383): [<ffffffff8160678c>]
kmem_cache_alloc+0x9c/0x2f0
[   90.355832] hardirqs last disabled at (282384): [<ffffffff8160674d>]
kmem_cache_alloc+0x5d/0x2f0
[   90.357066] softirqs last  enabled at (282196): [<ffffffff816daa87>]
wb_workfn+0x387/0xec0
[   90.358280] softirqs last disabled at (282194): [<ffffffff816da918>]
wb_workfn+0x218/0xec0
[   90.359426] ---[ end trace 71c4462c6227f0d8 ]---
[   90.360135] kmemleak: Cannot allocate a kmemleak_object structure
[   90.888624] a.out invoked oom-killer:
gfp_mask=0x6040d0(GFP_KERNEL|__GFP_COMP|__GFP_RECLAIMABLE), order=0,
oom_score_adj=0
[   90.890564] CPU: 0 PID: 22248 Comm: a.out Tainted: G        W        
5.0.0-rc1+ #6
[   90.891793] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[   90.893263] Call Trace:
[   90.893678]  dump_stack+0xca/0x13e
[   90.894242]  dump_header+0x108/0xaef
[   90.894822]  ? ___ratelimit+0x5b/0x436
[   90.895430]  oom_kill_process.cold.38+0x10/0xa87
[   90.896164]  ? lock_downgrade+0x5d0/0x5d0
[   90.896806]  ? _raw_spin_unlock+0x1f/0x30
[   90.897445]  ? oom_badness+0xc8/0x770
[   90.898045]  out_of_memory+0x32a/0x1ab0
[   90.898668]  ? oom_killer_disable+0x280/0x280
[   90.899365]  ? mutex_trylock+0x162/0x1a0
[   90.899998]  __alloc_pages_slowpath+0x1b7a/0x2220
[   90.900754]  ? warn_alloc+0x120/0x120
[   90.901344]  ? find_held_lock+0x33/0x1c0
[   90.901985]  __alloc_pages_nodemask+0x521/0x5f0
[   90.902723]  ? __alloc_pages_slowpath+0x2220/0x2220
[   90.903499]  ? mark_held_locks+0xc1/0x140
[   90.904137]  ? cache_grow_begin+0x28f/0x300
[   90.904807]  cache_grow_begin+0x95/0x300
[   90.905443]  fallback_alloc+0x1ce/0x270
[   90.906074]  kmem_cache_alloc+0x286/0x2f0
[   90.906720]  ? sock_destroy_inode+0x60/0x60
[   90.907392]  sock_alloc_inode+0x18/0x250
[   90.908021]  ? sock_destroy_inode+0x60/0x60
[   90.908690]  alloc_inode+0x5e/0x180
[   90.909254]  new_inode_pseudo+0x12/0xd0
[   90.909868]  sock_alloc+0x3c/0x270
[   90.910428]  __sock_create+0xbe/0x740
[   90.911026]  inet_ctl_sock_create+0x8c/0x1e0
[   90.911710]  ? inet_current_timestamp+0xc0/0xc0
[   90.912432]  ? rcu_read_lock_sched_held+0x10f/0x130
[   90.913205]  ? find_next_bit+0x101/0x130
[   90.913837]  icmpv6_sk_init+0x12a/0x2b0
[   90.914463]  ? inet6_net_init+0x437/0x7c0
[   90.915102]  ? icmpv6_err_convert+0x180/0x180
[   90.915799]  ? ac6_proc_init+0x5a/0x70
[   90.916402]  ? inet6_net_init+0x53b/0x7c0
[   90.917041]  ? icmpv6_err_convert+0x180/0x180
[   90.917734]  ops_init+0xb2/0x400
[   90.918265]  setup_net+0x24c/0x5e0
[   90.918817]  ? ops_init+0x400/0x400
[   90.919386]  copy_net_ns+0x1a2/0x270
[   90.919969]  create_new_namespaces+0x579/0x790
[   90.920676]  unshare_nsproxy_namespaces+0xc3/0x190
[   90.921435]  ksys_unshare+0x428/0x810
[   90.922029]  ? walk_process_tree+0x2c0/0x2c0
[   90.922712]  ? __change_pid+0x19c/0x2c0
[   90.923328]  ? _raw_write_unlock_irq+0x24/0x30
[   90.924038]  ? trace_hardirqs_on_thunk+0x1a/0x1c
[   90.924771]  ? trace_hardirqs_off_caller+0x55/0x1c0
[   90.925547]  __x64_sys_unshare+0x2d/0x40
[   90.926187]  do_syscall_64+0xbc/0x4e0
[   90.926777]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   90.927573] RIP: 0033:0x7f827ad52229
[   90.928146] Code: Bad RIP value.
[   90.928663] RSP: 002b:00007fff6ac6a6c8 EFLAGS: 00000217 ORIG_RAX:
0000000000000110
[   90.929837] RAX: ffffffffffffffda RBX: 0000000000000000 RCX:
00007f827ad52229
[   90.930952] RDX: 00007f827ad27147 RSI: 0000000000000000 RDI:
0000000040000000
[   90.932056] RBP: 00007fff6ac6a6d0 R08: 0000000000000005 R09:
00007fff6ac6a720
[   90.933165] R10: 0000000000000000 R11: 0000000000000217 R12:
00005607242822e0
[   90.934278] R13: 00007fff6ac6a830 R14: 0000000000000000 R15:
0000000000000000

I just guess that copy_net_ns func doesn't call net_free, and it makes OOM.

And, I found that

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 99d4148e0f90..38c474e4ab4c 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -50,12 +50,12 @@ struct bpf_prog;
 #define NETDEV_HASHENTRIES (1 << NETDEV_HASHBITS)

 struct net {
-       refcount_t              passive;        /* To decided when the
network
-                                                * namespace should be
freed.
-                                                */
        refcount_t              count;          /* To decided when the
network
                                                 *  namespace should be
shut down.
                                                 */
+       refcount_t              passive;        /* To decided when the
network
+                                                * namespace should be
freed.
+                                                */
        spinlock_t              rules_mod_lock;

        atomic64_t              cookie_gen;

this patch also works on this bug. (Just swap the order of net struct.)
I don't know why this patch works (I just thought that compiler
optimization issue can make this bug and try this one.)
I need to review code more on copy_net_ns().

Also, I reproduce this bug on Ubuntu 18.10 (4.18.0-10-generic) on VMWare
Workstation Pro 15.0.2 by C reproducer.

On 12/01/2019 5:41 오전, Kirill Tkhai wrote:
> On 11.01.2019 23:33, Eric W. Biederman wrote:
>> zzoru <zzoru007@...il.com> writes:
>>
>>> net/core: BUG in copy_net_ns() (net_namespace.c)
>> I don't understand this failure report at all.
>>
>> I don't see the connection to copy_net_ns().  And I don't see how the
>> suggested patch short of covering up a memory stomp could possibly make
>> a difference.
>>
>> What am I missing?
> I received 3 spam messages from this address today.
> We can simply ignore this report.
>
>>
>>> Hello,
>>>
>>> I've got the following error report while fuzzing the kernel with syzkaller.
>>>
>>> On commit 1bdbe227492075d058e37cb3d400e6468d0095b5
>>>
>>> Syzkaller hit 'WARNING in __alloc_pages_slowpath' bug.
>>>
>>> syz-executor561 (17453) used greatest stack depth: 25056 bytes left
>>> WARNING: CPU: 0 PID: 692 at mm/page_alloc.c:4415
>>> __alloc_pages_slowpath+0x1cb1/0x2220 mm/page_alloc.c:4386
>>> Kernel panic - not syncing: panic_on_warn set ...
>>> CPU: 0 PID: 692 Comm: kswapd0 Not tainted 5.0.0-rc1+ #4
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>>> Ubuntu-1.8.2-1ubuntu1 04/01/2014
>>> Call Trace:
>>>  __dump_stack lib/dump_stack.c:77 [inline]
>>>  dump_stack+0xca/0x13e lib/dump_stack.c:113
>>>  panic+0x278/0x5bf kernel/panic.c:214
>>>  __warn.cold.10+0x20/0x45 kernel/panic.c:571
>>>  report_bug+0x246/0x2d0 lib/bug.c:186
>>>  fixup_bug arch/x86/kernel/traps.c:178 [inline]
>>>  do_error_trap+0x123/0x1e0 arch/x86/kernel/traps.c:271
>>>  do_invalid_op+0x31/0x40 arch/x86/kernel/traps.c:290
>>>  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
>>> RIP: 0010:__alloc_pages_slowpath+0x1cb1/0x2220 mm/page_alloc.c:4415
>>> Code: 8b 84 24 a8 00 00 00 e9 ea f1 ff ff 85 d2 0f 85 0b 01 00 00 48 c7
>>> c7 c0 5e 55 84 e8 79 f8 23 02 e9 86 f9 ff ff 44 8b 74 24 0c <0f> 0b 48
>>> b8 00 00 00 00 00 fc ff df 48 8b 54 24 18 48 c1 ea 03 80
>>> RSP: 0018:ffff8880683fedb8 EFLAGS: 00010046
>>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 1ffff1100d07fda4
>>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88807ffdd528
>>> RBP: dffffc0000000000 R08: 0000000000000000 R09: 000000000000067a
>>> R10: 0000000000000000 R11: ffff88807ffdc487 R12: 0000000000000000
>>> R13: ffff8880683ff010 R14: 0000000000415a00 R15: ffff8880683ff010
>>>  __alloc_pages_nodemask+0x521/0x5f0 mm/page_alloc.c:4555
>>>  __alloc_pages include/linux/gfp.h:473 [inline]
>>>  __alloc_pages_node include/linux/gfp.h:486 [inline]
>>>  kmem_getpages mm/slab.c:1398 [inline]
>>>  cache_grow_begin+0x95/0x300 mm/slab.c:2666
>>>  fallback_alloc+0x1ce/0x270 mm/slab.c:3208
>>>  __do_cache_alloc mm/slab.c:3345 [inline]
>>>  slab_alloc mm/slab.c:3373 [inline]
>>>  kmem_cache_alloc+0x286/0x2f0 mm/slab.c:3541
>>>  create_object+0x83/0x880 mm/kmemleak.c:578
>>>  kmemleak_alloc_recursive include/linux/kmemleak.h:55 [inline]
>>>  slab_post_alloc_hook mm/slab.h:442 [inline]
>>>  slab_alloc mm/slab.c:3381 [inline]
>>>  kmem_cache_alloc+0x18f/0x2f0 mm/slab.c:3541
>>>  mempool_alloc+0x13e/0x340 mm/mempool.c:385
>>>  bio_alloc_bioset+0x36f/0x5d0 block/bio.c:489
>>>  bio_alloc include/linux/bio.h:393 [inline]
>>>  submit_bh_wbc.isra.57+0x128/0x680 fs/buffer.c:3061
>>>  __block_write_full_page+0x6e8/0xcd0 fs/buffer.c:1765
>>>  block_write_full_page+0x202/0x250 fs/buffer.c:2955
>>>  pageout mm/vmscan.c:865 [inline]
>>>  shrink_page_list+0x220f/0x3800 mm/vmscan.c:1383
>>>  shrink_inactive_list+0x3c2/0xaa0 mm/vmscan.c:1961
>>>  shrink_list mm/vmscan.c:2273 [inline]
>>>  shrink_node_memcg.constprop.83+0x4bf/0x10e0 mm/vmscan.c:2538
>>>  shrink_node+0x162/0xd10 mm/vmscan.c:2753
>>>  kswapd_shrink_node mm/vmscan.c:3516 [inline]
>>>  balance_pgdat+0x47f/0xc00 mm/vmscan.c:3674
>>>  kswapd+0x57c/0xde0 mm/vmscan.c:3929
>>>  kthread+0x347/0x410 kernel/kthread.c:246
>>>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
>>> Dumping ftrace buffer:
>>>    (ftrace buffer empty)
>>> Kernel Offset: disabled
>>> Rebooting in 86400 seconds..
>>>
>>>
>>> Syzkaller reproducer:
>>> # {Threaded:false Collide:false Repeat:true RepeatTimes:0 Procs:8
>>> Sandbox:none Fault:false FaultCall:-1 FaultNth:0 EnableTun:false
>>> UseTmpDir:true EnableCgroups:false EnableNetdev:true ResetNet:false
>>> HandleSegv:false Repro:false Trace:false}
>>> unshare(0x40000000)
>>>
>>>
>>> C reproducer:
>>> // autogenerated by syzkaller (https://github.com/google/syzkaller)
>>>
>>> #define _GNU_SOURCE
>>>
>>> #include <arpa/inet.h>
>>> #include <dirent.h>
>>> #include <endian.h>
>>> #include <errno.h>
>>> #include <fcntl.h>
>>> #include <net/if.h>
>>> #include <net/if_arp.h>
>>> #include <netinet/in.h>
>>> #include <sched.h>
>>> #include <signal.h>
>>> #include <stdarg.h>
>>> #include <stdbool.h>
>>> #include <stdint.h>
>>> #include <stdio.h>
>>> #include <stdlib.h>
>>> #include <string.h>
>>> #include <sys/ioctl.h>
>>> #include <sys/mount.h>
>>> #include <sys/prctl.h>
>>> #include <sys/resource.h>
>>> #include <sys/socket.h>
>>> #include <sys/stat.h>
>>> #include <sys/syscall.h>
>>> #include <sys/time.h>
>>> #include <sys/types.h>
>>> #include <sys/uio.h>
>>> #include <sys/wait.h>
>>> #include <time.h>
>>> #include <unistd.h>
>>>
>>> #include <linux/if_addr.h>
>>> #include <linux/if_ether.h>
>>> #include <linux/if_link.h>
>>> #include <linux/if_tun.h>
>>> #include <linux/in6.h>
>>> #include <linux/ip.h>
>>> #include <linux/neighbour.h>
>>> #include <linux/net.h>
>>> #include <linux/netlink.h>
>>> #include <linux/rtnetlink.h>
>>> #include <linux/tcp.h>
>>> #include <linux/veth.h>
>>>
>>> unsigned long long procid;
>>>
>>> static void sleep_ms(uint64_t ms)
>>> {
>>>   usleep(ms * 1000);
>>> }
>>>
>>> static uint64_t current_time_ms(void)
>>> {
>>>   struct timespec ts;
>>>   if (clock_gettime(CLOCK_MONOTONIC, &ts))
>>>     exit(1);
>>>   return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
>>> }
>>>
>>> static void use_temporary_dir(void)
>>> {
>>>   char tmpdir_template[] = "./syzkaller.XXXXXX";
>>>   char* tmpdir = mkdtemp(tmpdir_template);
>>>   if (!tmpdir)
>>>     exit(1);
>>>   if (chmod(tmpdir, 0777))
>>>     exit(1);
>>>   if (chdir(tmpdir))
>>>     exit(1);
>>> }
>>>
>>> static bool write_file(const char* file, const char* what, ...)
>>> {
>>>   char buf[1024];
>>>   va_list args;
>>>   va_start(args, what);
>>>   vsnprintf(buf, sizeof(buf), what, args);
>>>   va_end(args);
>>>   buf[sizeof(buf) - 1] = 0;
>>>   int len = strlen(buf);
>>>   int fd = open(file, O_WRONLY | O_CLOEXEC);
>>>   if (fd == -1)
>>>     return false;
>>>   if (write(fd, buf, len) != len) {
>>>     int err = errno;
>>>     close(fd);
>>>     errno = err;
>>>     return false;
>>>   }
>>>   close(fd);
>>>   return true;
>>> }
>>>
>>> static struct {
>>>   char* pos;
>>>   int nesting;
>>>   struct nlattr* nested[8];
>>>   char buf[1024];
>>> } nlmsg;
>>>
>>> static void netlink_init(int typ, int flags, const void* data, int size)
>>> {
>>>   memset(&nlmsg, 0, sizeof(nlmsg));
>>>   struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg.buf;
>>>   hdr->nlmsg_type = typ;
>>>   hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | flags;
>>>   memcpy(hdr + 1, data, size);
>>>   nlmsg.pos = (char*)(hdr + 1) + NLMSG_ALIGN(size);
>>> }
>>>
>>> static void netlink_attr(int typ, const void* data, int size)
>>> {
>>>   struct nlattr* attr = (struct nlattr*)nlmsg.pos;
>>>   attr->nla_len = sizeof(*attr) + size;
>>>   attr->nla_type = typ;
>>>   memcpy(attr + 1, data, size);
>>>   nlmsg.pos += NLMSG_ALIGN(attr->nla_len);
>>> }
>>>
>>> static void netlink_nest(int typ)
>>> {
>>>   struct nlattr* attr = (struct nlattr*)nlmsg.pos;
>>>   attr->nla_type = typ;
>>>   nlmsg.pos += sizeof(*attr);
>>>   nlmsg.nested[nlmsg.nesting++] = attr;
>>> }
>>>
>>> static void netlink_done(void)
>>> {
>>>   struct nlattr* attr = nlmsg.nested[--nlmsg.nesting];
>>>   attr->nla_len = nlmsg.pos - (char*)attr;
>>> }
>>>
>>> static int netlink_send(int sock)
>>> {
>>>   if (nlmsg.pos > nlmsg.buf + sizeof(nlmsg.buf) || nlmsg.nesting)
>>>     exit(1);
>>>   struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg.buf;
>>>   hdr->nlmsg_len = nlmsg.pos - nlmsg.buf;
>>>   struct sockaddr_nl addr;
>>>   memset(&addr, 0, sizeof(addr));
>>>   addr.nl_family = AF_NETLINK;
>>>   unsigned n = sendto(sock, nlmsg.buf, hdr->nlmsg_len, 0,
>>>                       (struct sockaddr*)&addr, sizeof(addr));
>>>   if (n != hdr->nlmsg_len)
>>>     exit(1);
>>>   n = recv(sock, nlmsg.buf, sizeof(nlmsg.buf), 0);
>>>   if (n < sizeof(struct nlmsghdr) + sizeof(struct nlmsgerr))
>>>     exit(1);
>>>   if (hdr->nlmsg_type != NLMSG_ERROR)
>>>     exit(1);
>>>   return -((struct nlmsgerr*)(hdr + 1))->error;
>>> }
>>>
>>> static void netlink_add_device_impl(const char* type, const char* name)
>>> {
>>>   struct ifinfomsg hdr;
>>>   memset(&hdr, 0, sizeof(hdr));
>>>   netlink_init(RTM_NEWLINK, NLM_F_EXCL | NLM_F_CREATE, &hdr, sizeof(hdr));
>>>   if (name)
>>>     netlink_attr(IFLA_IFNAME, name, strlen(name));
>>>   netlink_nest(IFLA_LINKINFO);
>>>   netlink_attr(IFLA_INFO_KIND, type, strlen(type));
>>> }
>>>
>>> static void netlink_add_device(int sock, const char* type, const char* name)
>>> {
>>>   netlink_add_device_impl(type, name);
>>>   netlink_done();
>>>   int err = netlink_send(sock);
>>>   (void)err;
>>> }
>>>
>>> static void netlink_add_veth(int sock, const char* name, const char* peer)
>>> {
>>>   netlink_add_device_impl("veth", name);
>>>   netlink_nest(IFLA_INFO_DATA);
>>>   netlink_nest(VETH_INFO_PEER);
>>>   nlmsg.pos += sizeof(struct ifinfomsg);
>>>   netlink_attr(IFLA_IFNAME, peer, strlen(peer));
>>>   netlink_done();
>>>   netlink_done();
>>>   netlink_done();
>>>   int err = netlink_send(sock);
>>>   (void)err;
>>> }
>>>
>>> static void netlink_add_hsr(int sock, const char* name, const char* slave1,
>>>                             const char* slave2)
>>> {
>>>   netlink_add_device_impl("hsr", name);
>>>   netlink_nest(IFLA_INFO_DATA);
>>>   int ifindex1 = if_nametoindex(slave1);
>>>   netlink_attr(IFLA_HSR_SLAVE1, &ifindex1, sizeof(ifindex1));
>>>   int ifindex2 = if_nametoindex(slave2);
>>>   netlink_attr(IFLA_HSR_SLAVE2, &ifindex2, sizeof(ifindex2));
>>>   netlink_done();
>>>   netlink_done();
>>>   int err = netlink_send(sock);
>>>   (void)err;
>>> }
>>>
>>> static void netlink_device_change(int sock, const char* name, bool up,
>>>                                   const char* master, const void* mac,
>>>                                   int macsize)
>>> {
>>>   struct ifinfomsg hdr;
>>>   memset(&hdr, 0, sizeof(hdr));
>>>   if (up)
>>>     hdr.ifi_flags = hdr.ifi_change = IFF_UP;
>>>   netlink_init(RTM_NEWLINK, 0, &hdr, sizeof(hdr));
>>>   netlink_attr(IFLA_IFNAME, name, strlen(name));
>>>   if (master) {
>>>     int ifindex = if_nametoindex(master);
>>>     netlink_attr(IFLA_MASTER, &ifindex, sizeof(ifindex));
>>>   }
>>>   if (macsize)
>>>     netlink_attr(IFLA_ADDRESS, mac, macsize);
>>>   int err = netlink_send(sock);
>>>   (void)err;
>>> }
>>>
>>> static int netlink_add_addr(int sock, const char* dev, const void* addr,
>>>                             int addrsize)
>>> {
>>>   struct ifaddrmsg hdr;
>>>   memset(&hdr, 0, sizeof(hdr));
>>>   hdr.ifa_family = addrsize == 4 ? AF_INET : AF_INET6;
>>>   hdr.ifa_prefixlen = addrsize == 4 ? 24 : 120;
>>>   hdr.ifa_scope = RT_SCOPE_UNIVERSE;
>>>   hdr.ifa_index = if_nametoindex(dev);
>>>   netlink_init(RTM_NEWADDR, NLM_F_CREATE | NLM_F_REPLACE, &hdr,
>>> sizeof(hdr));
>>>   netlink_attr(IFA_LOCAL, addr, addrsize);
>>>   netlink_attr(IFA_ADDRESS, addr, addrsize);
>>>   return netlink_send(sock);
>>> }
>>>
>>> static void netlink_add_addr4(int sock, const char* dev, const char* addr)
>>> {
>>>   struct in_addr in_addr;
>>>   inet_pton(AF_INET, addr, &in_addr);
>>>   int err = netlink_add_addr(sock, dev, &in_addr, sizeof(in_addr));
>>>   (void)err;
>>> }
>>>
>>> static void netlink_add_addr6(int sock, const char* dev, const char* addr)
>>> {
>>>   struct in6_addr in6_addr;
>>>   inet_pton(AF_INET6, addr, &in6_addr);
>>>   int err = netlink_add_addr(sock, dev, &in6_addr, sizeof(in6_addr));
>>>   (void)err;
>>> }
>>>
>>> #define DEV_IPV4 "172.20.20.%d"
>>> #define DEV_IPV6 "fe80::%02hx"
>>> #define DEV_MAC 0x00aaaaaaaaaa
>>> static void initialize_netdevices(void)
>>> {
>>>   char netdevsim[16];
>>>   sprintf(netdevsim, "netdevsim%d", (int)procid);
>>>   struct {
>>>     const char* type;
>>>     const char* dev;
>>>   } devtypes[] = {
>>>       {"ip6gretap", "ip6gretap0"}, {"bridge", "bridge0"},
>>>       {"vcan", "vcan0"},           {"bond", "bond0"},
>>>       {"team", "team0"},           {"dummy", "dummy0"},
>>>       {"nlmon", "nlmon0"},         {"caif", "caif0"},
>>>       {"batadv", "batadv0"},       {"vxcan", "vxcan1"},
>>>       {"netdevsim", netdevsim},    {"veth", 0},
>>>   };
>>>   const char* devmasters[] = {"bridge", "bond", "team"};
>>>   struct {
>>>     const char* name;
>>>     int macsize;
>>>     bool noipv6;
>>>   } devices[] = {
>>>       {"lo", ETH_ALEN},
>>>       {"sit0", 0},
>>>       {"bridge0", ETH_ALEN},
>>>       {"vcan0", 0, true},
>>>       {"tunl0", 0},
>>>       {"gre0", 0},
>>>       {"gretap0", ETH_ALEN},
>>>       {"ip_vti0", 0},
>>>       {"ip6_vti0", 0},
>>>       {"ip6tnl0", 0},
>>>       {"ip6gre0", 0},
>>>       {"ip6gretap0", ETH_ALEN},
>>>       {"erspan0", ETH_ALEN},
>>>       {"bond0", ETH_ALEN},
>>>       {"veth0", ETH_ALEN},
>>>       {"veth1", ETH_ALEN},
>>>       {"team0", ETH_ALEN},
>>>       {"veth0_to_bridge", ETH_ALEN},
>>>       {"veth1_to_bridge", ETH_ALEN},
>>>       {"veth0_to_bond", ETH_ALEN},
>>>       {"veth1_to_bond", ETH_ALEN},
>>>       {"veth0_to_team", ETH_ALEN},
>>>       {"veth1_to_team", ETH_ALEN},
>>>       {"veth0_to_hsr", ETH_ALEN},
>>>       {"veth1_to_hsr", ETH_ALEN},
>>>       {"hsr0", 0},
>>>       {"dummy0", ETH_ALEN},
>>>       {"nlmon0", 0},
>>>       {"vxcan1", 0, true},
>>>       {"caif0", ETH_ALEN},
>>>       {"batadv0", ETH_ALEN},
>>>       {netdevsim, ETH_ALEN},
>>>   };
>>>   int sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
>>>   if (sock == -1)
>>>     exit(1);
>>>   unsigned i;
>>>   for (i = 0; i < sizeof(devtypes) / sizeof(devtypes[0]); i++)
>>>     netlink_add_device(sock, devtypes[i].type, devtypes[i].dev);
>>>   for (i = 0; i < sizeof(devmasters) / (sizeof(devmasters[0])); i++) {
>>>     char master[32], slave0[32], veth0[32], slave1[32], veth1[32];
>>>     sprintf(slave0, "%s_slave_0", devmasters[i]);
>>>     sprintf(veth0, "veth0_to_%s", devmasters[i]);
>>>     netlink_add_veth(sock, slave0, veth0);
>>>     sprintf(slave1, "%s_slave_1", devmasters[i]);
>>>     sprintf(veth1, "veth1_to_%s", devmasters[i]);
>>>     netlink_add_veth(sock, slave1, veth1);
>>>     sprintf(master, "%s0", devmasters[i]);
>>>     netlink_device_change(sock, slave0, false, master, 0, 0);
>>>     netlink_device_change(sock, slave1, false, master, 0, 0);
>>>   }
>>>   netlink_device_change(sock, "bridge_slave_0", true, 0, 0, 0);
>>>   netlink_device_change(sock, "bridge_slave_1", true, 0, 0, 0);
>>>   netlink_add_veth(sock, "hsr_slave_0", "veth0_to_hsr");
>>>   netlink_add_veth(sock, "hsr_slave_1", "veth1_to_hsr");
>>>   netlink_add_hsr(sock, "hsr0", "hsr_slave_0", "hsr_slave_1");
>>>   netlink_device_change(sock, "hsr_slave_0", true, 0, 0, 0);
>>>   netlink_device_change(sock, "hsr_slave_1", true, 0, 0, 0);
>>>   for (i = 0; i < sizeof(devices) / (sizeof(devices[0])); i++) {
>>>     char addr[32];
>>>     sprintf(addr, DEV_IPV4, i + 10);
>>>     netlink_add_addr4(sock, devices[i].name, addr);
>>>     if (!devices[i].noipv6) {
>>>       sprintf(addr, DEV_IPV6, i + 10);
>>>       netlink_add_addr6(sock, devices[i].name, addr);
>>>     }
>>>     uint64_t macaddr = DEV_MAC + ((i + 10ull) << 40);
>>>     netlink_device_change(sock, devices[i].name, true, 0, &macaddr,
>>>                           devices[i].macsize);
>>>   }
>>>   close(sock);
>>> }
>>> static void initialize_netdevices_init(void)
>>> {
>>>   int sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
>>>   if (sock == -1)
>>>     exit(1);
>>>   struct {
>>>     const char* type;
>>>     int macsize;
>>>     bool noipv6;
>>>     bool noup;
>>>   } devtypes[] = {
>>>       {"nr", 7, true}, {"rose", 5, true, true},
>>>   };
>>>   unsigned i;
>>>   for (i = 0; i < sizeof(devtypes) / sizeof(devtypes[0]); i++) {
>>>     char dev[32], addr[32];
>>>     sprintf(dev, "%s%d", devtypes[i].type, (int)procid);
>>>     sprintf(addr, "172.30.%d.%d", i, (int)procid + 1);
>>>     netlink_add_addr4(sock, dev, addr);
>>>     if (!devtypes[i].noipv6) {
>>>       sprintf(addr, "fe88::%02hx:%02hx", i, (int)procid + 1);
>>>       netlink_add_addr6(sock, dev, addr);
>>>     }
>>>     int macsize = devtypes[i].macsize;
>>>     uint64_t macaddr = 0xbbbbbb +
>>>                        ((unsigned long long)i << (8 * (macsize - 2))) +
>>>                        (procid << (8 * (macsize - 1)));
>>>     netlink_device_change(sock, dev, !devtypes[i].noup, 0, &macaddr,
>>> macsize);
>>>   }
>>>   close(sock);
>>> }
>>>
>>> static void setup_common()
>>> {
>>>   if (mount(0, "/sys/fs/fuse/connections", "fusectl", 0, 0)) {
>>>   }
>>> }
>>>
>>> static void loop();
>>>
>>> static void sandbox_common()
>>> {
>>>   prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
>>>   setpgrp();
>>>   setsid();
>>>   struct rlimit rlim;
>>>   rlim.rlim_cur = rlim.rlim_max = 200 << 20;
>>>   setrlimit(RLIMIT_AS, &rlim);
>>>   rlim.rlim_cur = rlim.rlim_max = 32 << 20;
>>>   setrlimit(RLIMIT_MEMLOCK, &rlim);
>>>   rlim.rlim_cur = rlim.rlim_max = 136 << 20;
>>>   setrlimit(RLIMIT_FSIZE, &rlim);
>>>   rlim.rlim_cur = rlim.rlim_max = 1 << 20;
>>>   setrlimit(RLIMIT_STACK, &rlim);
>>>   rlim.rlim_cur = rlim.rlim_max = 0;
>>>   setrlimit(RLIMIT_CORE, &rlim);
>>>   rlim.rlim_cur = rlim.rlim_max = 256;
>>>   setrlimit(RLIMIT_NOFILE, &rlim);
>>>   if (unshare(CLONE_NEWNS)) {
>>>   }
>>>   if (unshare(CLONE_NEWIPC)) {
>>>   }
>>>   if (unshare(0x02000000)) {
>>>   }
>>>   if (unshare(CLONE_NEWUTS)) {
>>>   }
>>>   if (unshare(CLONE_SYSVSEM)) {
>>>   }
>>>   typedef struct {
>>>     const char* name;
>>>     const char* value;
>>>   } sysctl_t;
>>>   static const sysctl_t sysctls[] = {
>>>       {"/proc/sys/kernel/shmmax", "16777216"},
>>>       {"/proc/sys/kernel/shmall", "536870912"},
>>>       {"/proc/sys/kernel/shmmni", "1024"},
>>>       {"/proc/sys/kernel/msgmax", "8192"},
>>>       {"/proc/sys/kernel/msgmni", "1024"},
>>>       {"/proc/sys/kernel/msgmnb", "1024"},
>>>       {"/proc/sys/kernel/sem", "1024 1048576 500 1024"},
>>>   };
>>>   unsigned i;
>>>   for (i = 0; i < sizeof(sysctls) / sizeof(sysctls[0]); i++)
>>>     write_file(sysctls[i].name, sysctls[i].value);
>>> }
>>>
>>> int wait_for_loop(int pid)
>>> {
>>>   if (pid < 0)
>>>     exit(1);
>>>   int status = 0;
>>>   while (waitpid(-1, &status, __WALL) != pid) {
>>>   }
>>>   return WEXITSTATUS(status);
>>> }
>>>
>>> static int do_sandbox_none(void)
>>> {
>>>   if (unshare(CLONE_NEWPID)) {
>>>   }
>>>   int pid = fork();
>>>   if (pid != 0)
>>>     return wait_for_loop(pid);
>>>   setup_common();
>>>   sandbox_common();
>>>   initialize_netdevices_init();
>>>   if (unshare(CLONE_NEWNET)) {
>>>   }
>>>   initialize_netdevices();
>>>   loop();
>>>   exit(1);
>>> }
>>>
>>> #define FS_IOC_SETFLAGS _IOW('f', 2, long)
>>> static void remove_dir(const char* dir)
>>> {
>>>   DIR* dp;
>>>   struct dirent* ep;
>>>   int iter = 0;
>>> retry:
>>>   while (umount2(dir, MNT_DETACH) == 0) {
>>>   }
>>>   dp = opendir(dir);
>>>   if (dp == NULL) {
>>>     if (errno == EMFILE) {
>>>       exit(1);
>>>     }
>>>     exit(1);
>>>   }
>>>   while ((ep = readdir(dp))) {
>>>     if (strcmp(ep->d_name, ".") == 0 || strcmp(ep->d_name, "..") == 0)
>>>       continue;
>>>     char filename[FILENAME_MAX];
>>>     snprintf(filename, sizeof(filename), "%s/%s", dir, ep->d_name);
>>>     while (umount2(filename, MNT_DETACH) == 0) {
>>>     }
>>>     struct stat st;
>>>     if (lstat(filename, &st))
>>>       exit(1);
>>>     if (S_ISDIR(st.st_mode)) {
>>>       remove_dir(filename);
>>>       continue;
>>>     }
>>>     int i;
>>>     for (i = 0;; i++) {
>>>       if (unlink(filename) == 0)
>>>         break;
>>>       if (errno == EPERM) {
>>>         int fd = open(filename, O_RDONLY);
>>>         if (fd != -1) {
>>>           long flags = 0;
>>>           if (ioctl(fd, FS_IOC_SETFLAGS, &flags) == 0)
>>>             close(fd);
>>>           continue;
>>>         }
>>>       }
>>>       if (errno == EROFS) {
>>>         break;
>>>       }
>>>       if (errno != EBUSY || i > 100)
>>>         exit(1);
>>>       if (umount2(filename, MNT_DETACH))
>>>         exit(1);
>>>     }
>>>   }
>>>   closedir(dp);
>>>   int i;
>>>   for (i = 0;; i++) {
>>>     if (rmdir(dir) == 0)
>>>       break;
>>>     if (i < 100) {
>>>       if (errno == EPERM) {
>>>         int fd = open(dir, O_RDONLY);
>>>         if (fd != -1) {
>>>           long flags = 0;
>>>           if (ioctl(fd, FS_IOC_SETFLAGS, &flags) == 0)
>>>             close(fd);
>>>           continue;
>>>         }
>>>       }
>>>       if (errno == EROFS) {
>>>         break;
>>>       }
>>>       if (errno == EBUSY) {
>>>         if (umount2(dir, MNT_DETACH))
>>>           exit(1);
>>>         continue;
>>>       }
>>>       if (errno == ENOTEMPTY) {
>>>         if (iter < 100) {
>>>           iter++;
>>>           goto retry;
>>>         }
>>>       }
>>>     }
>>>     exit(1);
>>>   }
>>> }
>>>
>>> static void kill_and_wait(int pid, int* status)
>>> {
>>>   kill(-pid, SIGKILL);
>>>   kill(pid, SIGKILL);
>>>   int i;
>>>   for (i = 0; i < 100; i++) {
>>>     if (waitpid(-1, status, WNOHANG | __WALL) == pid)
>>>       return;
>>>     usleep(1000);
>>>   }
>>>   DIR* dir = opendir("/sys/fs/fuse/connections");
>>>   if (dir) {
>>>     for (;;) {
>>>       struct dirent* ent = readdir(dir);
>>>       if (!ent)
>>>         break;
>>>       if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0)
>>>         continue;
>>>       char abort[300];
>>>       snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort",
>>>                ent->d_name);
>>>       int fd = open(abort, O_WRONLY);
>>>       if (fd == -1) {
>>>         continue;
>>>       }
>>>       if (write(fd, abort, 1) < 0) {
>>>       }
>>>       close(fd);
>>>     }
>>>     closedir(dir);
>>>   } else {
>>>   }
>>>   while (waitpid(-1, status, __WALL) != pid) {
>>>   }
>>> }
>>>
>>> #define SYZ_HAVE_SETUP_TEST 1
>>> static void setup_test()
>>> {
>>>   prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
>>>   setpgrp();
>>> }
>>>
>>> #define SYZ_HAVE_RESET_TEST 1
>>> static void reset_test()
>>> {
>>>   int fd;
>>>   for (fd = 3; fd < 30; fd++)
>>>     close(fd);
>>> }
>>>
>>> static void execute_one(void);
>>>
>>> #define WAIT_FLAGS __WALL
>>>
>>> static void loop(void)
>>> {
>>>   int iter;
>>>   for (iter = 0;; iter++) {
>>>     char cwdbuf[32];
>>>     sprintf(cwdbuf, "./%d", iter);
>>>     if (mkdir(cwdbuf, 0777))
>>>       exit(1);
>>>     int pid = fork();
>>>     if (pid < 0)
>>>       exit(1);
>>>     if (pid == 0) {
>>>       if (chdir(cwdbuf))
>>>         exit(1);
>>>       setup_test();
>>>       execute_one();
>>>       reset_test();
>>>       exit(0);
>>>     }
>>>     int status = 0;
>>>     uint64_t start = current_time_ms();
>>>     for (;;) {
>>>       if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid)
>>>         break;
>>>       sleep_ms(1);
>>>       if (current_time_ms() - start < 5 * 1000)
>>>         continue;
>>>       kill_and_wait(pid, &status);
>>>       break;
>>>     }
>>>     remove_dir(cwdbuf);
>>>   }
>>> }
>>>
>>> void execute_one(void)
>>> {
>>>   syscall(__NR_unshare, 0x40000000);
>>> }
>>> int main(void)
>>> {
>>>   syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
>>>   for (procid = 0; procid < 8; procid++) {
>>>     if (fork() == 0) {
>>>       use_temporary_dir();
>>>       do_sandbox_none();
>>>     }
>>>   }
>>>   sleep(1000000);
>>>   return 0;
>>> }
>>>
>>>
>>> I reviewed kernel code and found a bug that
>>> net_drop_ns func doesn't call net_free func when refcount_dec_and_test's
>>> return value is zero.
>> Yes.  We don't call net_free when the reference count does not decrement
>> to zero.  The reference count is initialized to 1 a few lines above the
>> section of code in your patch so that should not be a problem.
>>
>>> or
>>> when rv = down_read_killable(&pernet_ops_rwsem) < 0, it doesn't need to
>>> call refcount_dec_and_test.
>> It doesn't need to but it should be harmless.
>>
>>> https://github.com/torvalds/linux/commit/5ba049a5cc8e24a1643df75bbf65b4efa070fa74#diff-9312644e2968a45510bacdd2b2872ad2
>>> (I can't reproduce this bug on v4.15 , and
>>> 1bdbe227492075d058e37cb3d400e6468d0095b5 with my patch. Because of the
>>> previous version of kernel doesn't have this bug.)
>>> This bug can lead to memory leak or DOS.
>>>
>>> I made a patch for this bug. (just revert to a before commit)
>> What am I missing?
>>
>> The only thing I can see your patch doing is covering up a memory stomp
>> that has the effect of changing the value of net->passive.  I am not
>> really keen on hiding bugs of that kind.
>>
>>
>>> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
>>> index b02fb19df2cc..9de0ade14956 100644
>>> --- a/net/core/net_namespace.c
>>> +++ b/net/core/net_namespace.c
>>> @@ -431,15 +431,18 @@ struct net *copy_net_ns(unsigned long flags,
>>>         get_user_ns(user_ns);
>>>
>>>         rv = down_read_killable(&pernet_ops_rwsem);
>>> -       if (rv < 0)
>>> -               goto put_userns;
>>> +       if (rv < 0){
>>> +        net_free(net);
>>> +        dec_net_namespaces(ucounts);
>>> +        put_user_ns(user_ns);
>>> +        return ERR_PTR(rv);
>>> +    }
>>>
>>>         rv = setup_net(net, user_ns);
>>>
>>>         up_read(&pernet_ops_rwsem);
>>>
>>>         if (rv < 0) {
>>> -put_userns:
>>>                 put_user_ns(user_ns);
>>>                 net_drop_ns(net);
>>>  dec_ucounts:
>>>
>>> and, sorry for my encrypted mails.
>> Eric
>>

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