Re: possible deadlock in rtnl_lock (4)

[Xin Long]

On Thu, Feb 8, 2018 at 6:58 AM, syzbot
<syzbot+ddde1c7b7ff7442d7f2d@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> 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.
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.
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