Subject: possible deadlock in inet_stream_connect

From: syzbot <[email-masked]>
Date: Wed, 17 Feb 2021 09:30:23 -0800

Hello,

syzbot found the following issue on:

HEAD commit:    9ec5eea5 lib/parman: Delete newline
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11380d24d00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dbc1ca9e55dc1f9f
dashboard link: https://syzkaller.appspot.com/bug?extid=b0f5178b61ed7f3bbb46
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=177a6d14d00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10caeb02d00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

============================================
WARNING: possible recursive locking detected
5.11.0-rc7-syzkaller #0 Not tainted
--------------------------------------------
syz-executor845/10119 is trying to acquire lock:
ffff888021e6e320 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
ffff888021e6e320 (sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_stream_connect+0x3f/0xa0 net/ipv4/af_inet.c:724

but task is already holding lock:
ffff888022c1a520 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
ffff888022c1a520 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_stream_connect+0x85/0x800 net/mptcp/protocol.c:3171

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-executor845/10119:
 #0: ffff888022c1a520 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
 #0: ffff888022c1a520 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_stream_connect+0x85/0x800 net/mptcp/protocol.c:3171

stack backtrace:
CPU: 0 PID: 10119 Comm: syz-executor845 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 print_deadlock_bug kernel/locking/lockdep.c:2761 [inline]
 check_deadlock kernel/locking/lockdep.c:2804 [inline]
 validate_chain kernel/locking/lockdep.c:3595 [inline]
 __lock_acquire.cold+0x114/0x39e kernel/locking/lockdep.c:4832
 lock_acquire kernel/locking/lockdep.c:5442 [inline]
 lock_acquire+0x1a8/0x720 kernel/locking/lockdep.c:5407
 lock_sock_nested+0xc5/0x110 net/core/sock.c:3071
 lock_sock include/net/sock.h:1598 [inline]
 inet_stream_connect+0x3f/0xa0 net/ipv4/af_inet.c:724
 mptcp_stream_connect+0x156/0x800 net/mptcp/protocol.c:3200
 __sys_connect_file+0x155/0x1a0 net/socket.c:1835
 __sys_connect+0x161/0x190 net/socket.c:1852
 __do_sys_connect net/socket.c:1862 [inline]
 __se_sys_connect net/socket.c:1859 [inline]
 __x64_sys_connect+0x6f/0xb0 net/socket.c:1859
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x443ce9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 a1 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff5f9324e8 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000443ce9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 000000a800000000 R09: 000000a800000000
R10: 000000a800000000 R11: 0000000000000246 R12: 00007fff5f932500
R13: 00007fff5f932510 R14: 0000000000014e11 R15: 00007fff5f9324f0

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