net/sctp: recursive locking in sctp_do_peeloff

[Dmitry Vyukov]

Hello,

I've got the following recursive locking report while running
syzkaller fuzzer on net-next/9c28286b1b4b9bce6e35dd4c8a1265f03802a89a:

[ INFO: possible recursive locking detected ]
4.10.0+ #14 Not tainted
---------------------------------------------
syz-executor3/5560 is trying to acquire lock:
 (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff8401ebcd>] lock_sock
include/net/sock.h:1460 [inline]
 (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff8401ebcd>]
sctp_close+0xcd/0x9d0 net/sctp/socket.c:1497

but task is already holding lock:
 (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff84038110>] lock_sock
include/net/sock.h:1460 [inline]
 (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff84038110>]
sctp_getsockopt+0x450/0x67e0 net/sctp/socket.c:6611

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(sk_lock-AF_INET6);
  lock(sk_lock-AF_INET6);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz-executor3/5560:
 #0:  (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff84038110>] lock_sock
include/net/sock.h:1460 [inline]
 #0:  (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff84038110>]
sctp_getsockopt+0x450/0x67e0 net/sctp/socket.c:6611

stack backtrace:
CPU: 0 PID: 5560 Comm: syz-executor3 Not tainted 4.10.0+ #14
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x2ee/0x3ef lib/dump_stack.c:52
 print_deadlock_bug kernel/locking/lockdep.c:1729 [inline]
 check_deadlock kernel/locking/lockdep.c:1773 [inline]
 validate_chain kernel/locking/lockdep.c:2251 [inline]
 __lock_acquire+0xef2/0x3430 kernel/locking/lockdep.c:3340
 lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
 lock_sock_nested+0xcb/0x120 net/core/sock.c:2536
 lock_sock include/net/sock.h:1460 [inline]
 sctp_close+0xcd/0x9d0 net/sctp/socket.c:1497
 inet_release+0xed/0x1c0 net/ipv4/af_inet.c:425
 inet6_release+0x50/0x70 net/ipv6/af_inet6.c:432
 sock_release+0x8d/0x1e0 net/socket.c:597
 __sock_create+0x38b/0x870 net/socket.c:1226
 sock_create+0x7f/0xa0 net/socket.c:1237
 sctp_do_peeloff+0x1a2/0x440 net/sctp/socket.c:4879
 sctp_getsockopt_peeloff net/sctp/socket.c:4914 [inline]
 sctp_getsockopt+0x111a/0x67e0 net/sctp/socket.c:6628
 sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2690
 SYSC_getsockopt net/socket.c:1817 [inline]
 SyS_getsockopt+0x240/0x380 net/socket.c:1799
 entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x44fb79
RSP: 002b:00007f35f232bb58 EFLAGS: 00000212 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 0000000000000084 RCX: 000000000044fb79
RDX: 0000000000000066 RSI: 0000000000000084 RDI: 0000000000000006
RBP: 0000000000000006 R08: 0000000020119000 R09: 0000000000000000
R10: 000000002058dff8 R11: 0000000000000212 R12: 0000000000708000
R13: 0000000000000103 R14: 0000000000000001 R15: 0000000000000000