net/ipv4: deadlock in ip_ra_control

[Dmitry Vyukov]

Hello,

I've got the following deadlock report while running syzkaller fuzzer
on linux-next/51788aebe7cae79cb334ad50641347465fc188fd:

======================================================
[ INFO: possible circular locking dependency detected ]
4.10.0-next-20170301+ #1 Not tainted
-------------------------------------------------------
syz-executor1/3394 is trying to acquire lock:
 (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff838864cc>] lock_sock
include/net/sock.h:1460 [inline]
 (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff838864cc>]
do_ip_setsockopt.isra.12+0x21c/0x3540 net/ipv4/ip_sockglue.c:652

but task is already holding lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff836fbd97>] rtnl_lock+0x17/0x20
net/core/rtnetlink.c:70

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (rtnl_mutex){+.+.+.}:
       validate_chain kernel/locking/lockdep.c:2265 [inline]
       __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
       lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
       __mutex_lock_common kernel/locking/mutex.c:754 [inline]
       __mutex_lock+0x172/0x1730 kernel/locking/mutex.c:891
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:906
       rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
       mrtsock_destruct+0x86/0x2c0 net/ipv4/ipmr.c:1281
       ip_ra_control+0x459/0x600 net/ipv4/ip_sockglue.c:372
       do_ip_setsockopt.isra.12+0x1064/0x3540 net/ipv4/ip_sockglue.c:1161
       ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1264
       raw_setsockopt+0xb7/0xd0 net/ipv4/raw.c:839
       sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2725
       SYSC_setsockopt net/socket.c:1786 [inline]
       SyS_setsockopt+0x25c/0x390 net/socket.c:1765
       entry_SYSCALL_64_fastpath+0x1f/0xc2

-> #0 (sk_lock-AF_INET){+.+.+.}:
       check_prev_add kernel/locking/lockdep.c:1828 [inline]
       check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1938
       validate_chain kernel/locking/lockdep.c:2265 [inline]
       __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
       lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
       lock_sock_nested+0xcb/0x120 net/core/sock.c:2530
       lock_sock include/net/sock.h:1460 [inline]
       do_ip_setsockopt.isra.12+0x21c/0x3540 net/ipv4/ip_sockglue.c:652
       ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1264
       tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2721
       sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2725
       SYSC_setsockopt net/socket.c:1786 [inline]
       SyS_setsockopt+0x25c/0x390 net/socket.c:1765
       entry_SYSCALL_64_fastpath+0x1f/0xc2

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz-executor1/3394:
 #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff836fbd97>]
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70

stack backtrace:
CPU: 0 PID: 3394 Comm: syz-executor1 Not tainted 4.10.0-next-20170301+ #1
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:15 [inline]
 dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
 print_circular_bug+0x307/0x3b0 kernel/locking/lockdep.c:1202
 check_prev_add kernel/locking/lockdep.c:1828 [inline]
 check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1938
 validate_chain kernel/locking/lockdep.c:2265 [inline]
 __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
 lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
 lock_sock_nested+0xcb/0x120 net/core/sock.c:2530
 lock_sock include/net/sock.h:1460 [inline]
 do_ip_setsockopt.isra.12+0x21c/0x3540 net/ipv4/ip_sockglue.c:652
 ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1264
 tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2721
 sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2725
 SYSC_setsockopt net/socket.c:1786 [inline]
 SyS_setsockopt+0x25c/0x390 net/socket.c:1765
 entry_SYSCALL_64_fastpath+0x1f/0xc2