Date:   Thu, 8 Feb 2018 14:25:27 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     syzbot <syzbot+ddde1c7b7ff7442d7f2d@...kaller.appspotmail.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        davem <davem@...emloft.net>, David Ahern <dsahern@...il.com>,
        Florian Westphal <fw@...len.de>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jiri Benc <jbenc@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        mschiffer@...verse-factory.net,
        network dev <netdev@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        Vlad Yasevich <vyasevich@...il.com>
Subject: Re: possible deadlock in rtnl_lock (4)

On Thu, Feb 8, 2018 at 10:54 AM, Xin Long <lucien.xin@...il.com> wrote:
> On Thu, Feb 8, 2018 at 6:58 AM, syzbot
> <syzbot+ddde1c7b7ff7442d7f2d@...kaller.appspotmail.com> wrote:
>> Hello,
>>
>> syzbot hit the following crash on upstream commit
>> a2e5790d841658485d642196dbb0927303d6c22f (Wed Feb 7 06:15:42 2018 +0000)
>> Merge branch 'akpm' (patches from Andrew)
>>
>> So far this crash happened 632 times on
>> https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/master.
>> C reproducer is attached.
>> syzkaller reproducer is attached.
>> Raw console output is attached.
>> compiler: gcc (GCC) 7.1.1 20170620
>> .config is attached.
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+ddde1c7b7ff7442d7f2d@...kaller.appspotmail.com
>> It will help syzbot understand when the bug is fixed. See footer for
>> details.
>> If you forward the report, please keep this part and the footer.
>>
>>
>> ======================================================
>> WARNING: possible circular locking dependency detected
>> 4.15.0+ #301 Not tainted
>> ------------------------------------------------------
>> syzkaller233489/4179 is trying to acquire lock:
>>  (rtnl_mutex){+.+.}, at: [<0000000048e996fd>] rtnl_lock+0x17/0x20
>> net/core/rtnetlink.c:74
>>
>> but task is already holding lock:
>>  (&xt[i].mutex){+.+.}, at: [<00000000328553a2>]
>> xt_find_table_lock+0x3e/0x3e0 net/netfilter/x_tables.c:1041
>>
>> which lock already depends on the new lock.
>>
>>
>> the existing dependency chain (in reverse order) is:
>>
>> -> #2 (&xt[i].mutex){+.+.}:
>>        __mutex_lock_common kernel/locking/mutex.c:756 [inline]
>>        __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
>>        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>>        xt_find_table_lock+0x3e/0x3e0 net/netfilter/x_tables.c:1041
>>        xt_request_find_table_lock+0x28/0xc0 net/netfilter/x_tables.c:1088
>>        get_info+0x154/0x690 net/ipv6/netfilter/ip6_tables.c:989
>>        do_ipt_get_ctl+0x159/0xac0 net/ipv4/netfilter/ip_tables.c:1699
>>        nf_sockopt net/netfilter/nf_sockopt.c:104 [inline]
>>        nf_getsockopt+0x6a/0xc0 net/netfilter/nf_sockopt.c:122
>>        ip_getsockopt+0x15c/0x220 net/ipv4/ip_sockglue.c:1571
>>        tcp_getsockopt+0x82/0xd0 net/ipv4/tcp.c:3359
>>        sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2934
>>        SYSC_getsockopt net/socket.c:1880 [inline]
>>        SyS_getsockopt+0x178/0x340 net/socket.c:1862
>>        do_syscall_64+0x282/0x940 arch/x86/entry/common.c:287
>>        entry_SYSCALL_64_after_hwframe+0x26/0x9b
>>
>> -> #1 (sk_lock-AF_INET){+.+.}:
>>        lock_sock_nested+0xc2/0x110 net/core/sock.c:2777
>>        lock_sock include/net/sock.h:1463 [inline]
>>        do_ip_setsockopt.isra.12+0x1d9/0x3210 net/ipv4/ip_sockglue.c:646
>>        ip_setsockopt+0x3a/0xa0 net/ipv4/ip_sockglue.c:1252
>>        udp_setsockopt+0x45/0x80 net/ipv4/udp.c:2401
>>        sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2975
>>        SYSC_setsockopt net/socket.c:1849 [inline]
>>        SyS_setsockopt+0x189/0x360 net/socket.c:1828
>>        do_syscall_64+0x282/0x940 arch/x86/entry/common.c:287
>>        entry_SYSCALL_64_after_hwframe+0x26/0x9b
>>
>> -> #0 (rtnl_mutex){+.+.}:
>>        lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
>>        __mutex_lock_common kernel/locking/mutex.c:756 [inline]
>>        __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
>>        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>>        rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
>>        unregister_netdevice_notifier+0x91/0x4e0 net/core/dev.c:1673
>>        clusterip_config_entry_put net/ipv4/netfilter/ipt_CLUSTERIP.c:114
>> [inline]
>>        clusterip_tg_destroy+0x389/0x6e0
>> net/ipv4/netfilter/ipt_CLUSTERIP.c:518
>>        cleanup_entry+0x218/0x350 net/ipv4/netfilter/ip_tables.c:654
>>        __do_replace+0x79d/0xa50 net/ipv4/netfilter/ip_tables.c:1089
>>        do_replace net/ipv4/netfilter/ip_tables.c:1145 [inline]
>>        do_ipt_set_ctl+0x40f/0x5f0 net/ipv4/netfilter/ip_tables.c:1675
>>        nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
>>        nf_setsockopt+0x67/0xc0 net/netfilter/nf_sockopt.c:115
>>        ip_setsockopt+0x97/0xa0 net/ipv4/ip_sockglue.c:1259
>>        tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2905
>>        sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2975
>>        SYSC_setsockopt net/socket.c:1849 [inline]
>>        SyS_setsockopt+0x189/0x360 net/socket.c:1828
>>        do_syscall_64+0x282/0x940 arch/x86/entry/common.c:287
>>        entry_SYSCALL_64_after_hwframe+0x26/0x9b
>>
>> other info that might help us debug this:
>>
>> Chain exists of:
>>   rtnl_mutex --> sk_lock-AF_INET --> &xt[i].mutex
>>
>>  Possible unsafe locking scenario:
>>
>>        CPU0                    CPU1
>>        ----                    ----
>>   lock(&xt[i].mutex);
>>                                lock(sk_lock-AF_INET);
>>                                lock(&xt[i].mutex);
>>   lock(rtnl_mutex);
>>
>>  *** DEADLOCK ***
>
> It's probably just a warning.

We are also seeing some "task hung for 120 seconds on rtnl_lock"
warnings lately. However, they are not preceded by any lockdep
warnings, which is strange.


> I'm thinking an improment that moves up xt_table_unlock(t) in __do_replace():
>
> +++ b/net/ipv4/netfilter/ip_tables.c
> @@ -1082,6 +1082,8 @@ static int get_info(struct net *net, void __user *user,
>             (newinfo->number <= oldinfo->initial_entries))
>                 module_put(t->me);
>
> +       xt_table_unlock(t);
> +
>         get_old_counters(oldinfo, counters);
>
>         /* Decrease module usage counts and free resource */
> @@ -1095,7 +1097,6 @@ static int get_info(struct net *net, void __user *user,
>                 net_warn_ratelimited("iptables: counters copy to user
> failed while replacing table\n");
>         }
>         vfree(counters);
> -       xt_table_unlock(t);
>         return ret;
>
> It should be safe, as 'oldinfo' doesn't belong to this table anymore there,
> no need to protect it by xt[i].mutex. It could also avoid this warning.
> I need to do some testings to confirm this.
>
>>
>> 1 lock held by syzkaller233489/4179:
>>  #0:  (&xt[i].mutex){+.+.}, at: [<00000000328553a2>]
>> xt_find_table_lock+0x3e/0x3e0 net/netfilter/x_tables.c:1041
>>
>> stack backtrace:
>> CPU: 1 PID: 4179 Comm: syzkaller233489 Not tainted 4.15.0+ #301
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:17 [inline]
>>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>>  print_circular_bug.isra.38+0x2cd/0x2dc kernel/locking/lockdep.c:1223
>>  check_prev_add kernel/locking/lockdep.c:1863 [inline]
>>  check_prevs_add kernel/locking/lockdep.c:1976 [inline]
>>  validate_chain kernel/locking/lockdep.c:2417 [inline]
>>  __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3431
>>  lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
>>  __mutex_lock_common kernel/locking/mutex.c:756 [inline]
>>  __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
>>  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>>  rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
>>  unregister_netdevice_notifier+0x91/0x4e0 net/core/dev.c:1673
>>  clusterip_config_entry_put net/ipv4/netfilter/ipt_CLUSTERIP.c:114 [inline]
>>  clusterip_tg_destroy+0x389/0x6e0 net/ipv4/netfilter/ipt_CLUSTERIP.c:518
>>  cleanup_entry+0x218/0x350 net/ipv4/netfilter/ip_tables.c:654
>>  __do_replace+0x79d/0xa50 net/ipv4/netfilter/ip_tables.c:1089
>>  do_replace net/ipv4/netfilter/ip_tables.c:1145 [inline]
>>  do_ipt_set_ctl+0x40f/0x5f0 net/ipv4/netfilter/ip_tables.c:1675
>>  nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
>>  nf_setsockopt+0x67/0xc0 net/netfilter/nf_sockopt.c:115
>>  ip_setsockopt+0x97/0xa0 net/ipv4/ip_sockglue.c:1259
>>  tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2905
>>  sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2975
>>  SYSC_setsockopt net/socket.c:1849 [inline]
>>  SyS_setsockopt+0x189/0x360 net/socket.c:1828
>>  do_syscall_64+0x282/0x940 arch/x86/entry/common.c:287
>>  entry_SYSCALL_64_after_hwframe+0x26/0x9b
>> RIP: 0033:0x44428a
>> RSP: 002b:00007fff903974a8 EFLAGS: 00000206 ORIG_RAX: 0000000000000036
>> RAX: ffffffffffffffda RBX: 00000000006cc100 RCX: 000000000044428a
>> RDX: 0000000000000040 RSI: 0000000000000000 RDI: 0000000000000003
>> RBP: 00000000006cc100 R08: 00000000000002d8 R09: 0000000000cbe880
>> R10: 00000000006cc528 R11: 0000000000000206 R12: 0000000000000003
>> R13: 00000000006cf0a8 R14: 00000000006cf050 R15: 00000000004a322e
>>
>>
>> ---
>> This bug is generated by a dumb bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for details.
>> Direct all questions to syzkaller@...glegroups.com.
>>
>> syzbot will keep track of this bug report.
>> If you forgot to add the Reported-by tag, once the fix for this bug is
>> merged
>> into any tree, please reply to this email with:
>> #syz fix: exact-commit-title
>> If you want to test a patch for this bug, please reply with:
>> #syz test: git://repo/address.git branch
>> and provide the patch inline or as an attachment.
>> To mark this as a duplicate of another syzbot report, please reply with:
>> #syz dup: exact-subject-of-another-report
>> If it's a one-off invalid bug report, please reply with:
>> #syz invalid
>> Note: if the crash happens again, it will cause creation of a new bug
>> report.
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