Re: possible deadlock in rtnl_lock (2)

On Sat, Feb 3, 2018 at 12:25 PM, Xin Long [off-list ref] wrote:

On Thu, Feb 1, 2018 at 7:58 PM, syzbot
[off-list ref] wrote:

quoted

Hello,

syzbot hit the following crash on upstream commit
255442c93843f52b6891b21d0b485bf2c97f93c3 (Thu Feb 1 03:25:25 2018 +0000)
Merge tag 'docs-4.16' of git://git.lwn.net/linux

So far this crash happened 1587 times on net-next, upstream.
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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Reported-by: syzbot+61e4972c2b1d5e08a5c2@syzkaller.appspotmail.com
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======================================================
WARNING: possible circular locking dependency detected
4.15.0+ #290 Not tainted
------------------------------------------------------
syzkaller681093/4124 is trying to acquire lock:
 (rtnl_mutex){+.+.}, at: [<00000000c3d62391>] rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74

but task is already holding lock:
 (sk_lock-AF_INET){+.+.}, at: [<0000000051813e83>] lock_sock
include/net/sock.h:1461 [inline]
 (sk_lock-AF_INET){+.+.}, at: [<0000000051813e83>] ip_setsockopt+0x8c/0xb0
net/ipv4/ip_sockglue.c:1259

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_INET){+.+.}:
       lock_sock_nested+0xc2/0x110 net/core/sock.c:2780
       lock_sock include/net/sock.h:1461 [inline]
       do_ip_getsockopt+0x1b3/0x2170 net/ipv4/ip_sockglue.c:1335
       ip_getsockopt+0x90/0x220 net/ipv4/ip_sockglue.c:1566
       tcp_getsockopt+0x82/0xd0 net/ipv4/tcp.c:3359
       sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2937
       SYSC_getsockopt net/socket.c:1880 [inline]
       SyS_getsockopt+0x178/0x340 net/socket.c:1862
       entry_SYSCALL_64_fastpath+0x29/0xa0

-> #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
       register_netdevice_notifier+0xad/0x860 net/core/dev.c:1607
       tee_tg_check+0x1a0/0x280 net/netfilter/xt_TEE.c:106
       xt_check_target+0x22c/0x7d0 net/netfilter/x_tables.c:845
       check_target net/ipv4/netfilter/ip_tables.c:513 [inline]
       find_check_entry.isra.8+0x8c8/0xcb0
net/ipv4/netfilter/ip_tables.c:554
       translate_table+0xed1/0x1610 net/ipv4/netfilter/ip_tables.c:725
       do_replace net/ipv4/netfilter/ip_tables.c:1141 [inline]
       do_ipt_set_ctl+0x370/0x5f0 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+0xa1/0xb0 net/ipv4/ip_sockglue.c:1260
       sctp_setsockopt+0x2b6/0x61d0 net/sctp/socket.c:4104
       sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2978
       SYSC_setsockopt net/socket.c:1849 [inline]
       SyS_setsockopt+0x189/0x360 net/socket.c:1828
       entry_SYSCALL_64_fastpath+0x29/0xa0

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_INET);
                               lock(rtnl_mutex);
                               lock(sk_lock-AF_INET);
  lock(rtnl_mutex);

 *** DEADLOCK ***

1 lock held by syzkaller681093/4124:
 #0:  (sk_lock-AF_INET){+.+.}, at: [<0000000051813e83>] lock_sock
include/net/sock.h:1461 [inline]
 #0:  (sk_lock-AF_INET){+.+.}, at: [<0000000051813e83>]
ip_setsockopt+0x8c/0xb0 net/ipv4/ip_sockglue.c:1259

stack backtrace:
CPU: 0 PID: 4124 Comm: syzkaller681093 Not tainted 4.15.0+ #290
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
 register_netdevice_notifier+0xad/0x860 net/core/dev.c:1607
 tee_tg_check+0x1a0/0x280 net/netfilter/xt_TEE.c:106
 xt_check_target+0x22c/0x7d0 net/netfilter/x_tables.c:845
 check_target net/ipv4/netfilter/ip_tables.c:513 [inline]
 find_check_entry.isra.8+0x8c8/0xcb0 net/ipv4/netfilter/ip_tables.c:554
 translate_table+0xed1/0x1610 net/ipv4/netfilter/ip_tables.c:725
 do_replace net/ipv4/netfilter/ip_tables.c:1141 [inline]
 do_ipt_set_ctl+0x370/0x5f0 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+0xa1/0xb0 net/ipv4/ip_sockglue.c:1260
 sctp_setsockopt+0x2b6/0x61d0 net/sctp/socket.c:4104
 sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2978
 SYSC_setsockopt net/socket.c:1849 [inline]
 SyS_setsockopt+0x189/0x360 net/socket.c:1828
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x445bd9
RSP: 002b:00007fffdfb6a998 EFLAGS: 00000203 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000445bd9
RDX: 0000000000000040 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007fffdfb6aa48 R08: 0000000000000318 R09: 0000000000000000
R10: 000000002


---
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I guess Paolo had already fixed it in this commit:

commit 3f34cfae1238848fd53f25e5c8fd59da57901f4b
Author: Paolo Abeni [off-list ref]
Date:   Tue Jan 30 19:01:40 2018 +0100

    netfilter: on sockopt() acquire sock lock only in the required scope

Pls check if it's already in this kernel.

"netfilter: on sockopt() acquire sock lock only in the required scope"
wasn't yet in the upstream tree when the bug was detected.
Let's tell syzbot that this is fixed:

#syz fix: netfilter: on sockopt() acquire sock lock only in the required scope