possible deadlock in rtnl_lock (4)

[syzbot]

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.

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======================================================
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 ***

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


---
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[Xin Long]

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.

[Dmitry Vyukov]

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.

[Xin Long]

Paolo noticed this warning actually could trigger a deadlock,
just need 3 processes, he already posted a fix:
[PATCH net v2] netfilter: drop outermost socket lock in getsockopt()

Let's see if it would also fix these panicks. Otherwise, I will try to
move this rtnl_lock out of the xt_lock as the below patch.