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Date:   Tue, 9 Aug 2022 14:12:47 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     <syzbot+ed5155f1684f6cab8abc@...kaller.appspotmail.com>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <kuniyu@...zon.com>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, <pabeni@...hat.com>,
        <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] possible deadlock in sk_diag_fill (4)

From:   syzbot <syzbot+ed5155f1684f6cab8abc@...kaller.appspotmail.com>
Date:   Tue, 09 Aug 2022 13:20:22 -0700
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    cb71b93c2dc3 Add linux-next specific files for 20220628
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=17f69c12080000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=badbc1adb2d582eb
> dashboard link: https://syzkaller.appspot.com/bug?extid=ed5155f1684f6cab8abc
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ed5155f1684f6cab8abc@...kaller.appspotmail.com
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.19.0-rc4-next-20220628-syzkaller #0 Not tainted
> ------------------------------------------------------
> syz-executor.3/3509 is trying to acquire lock:
> ffff8880765fae70 (&u->lock/1){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:87 [inline]
> ffff8880765fae70 (&u->lock/1){+.+.}-{2:2}, at: sk_diag_fill+0xaaf/0x10d0 net/unix/diag.c:155
> 
> but task is already holding lock:
> ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:360 [inline]
> ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:69 [inline]
> ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_fill+0x9c3/0x10d0 net/unix/diag.c:155
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #1 (rlock-AF_UNIX){+.+.}-{2:2}:
>        __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>        _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:162
>        skb_queue_tail+0x21/0x140 net/core/skbuff.c:3371
>        unix_dgram_sendmsg+0xf5a/0x1b60 net/unix/af_unix.c:2015
>        sock_sendmsg_nosec net/socket.c:714 [inline]
>        sock_sendmsg+0xcf/0x120 net/socket.c:734
>        io_send+0x26b/0x780 io_uring/net.c:266
>        io_issue_sqe+0x15e/0xd20 io_uring/io_uring.c:1601
>        io_queue_sqe io_uring/io_uring.c:1778 [inline]
>        io_submit_sqe io_uring/io_uring.c:2036 [inline]
>        io_submit_sqes+0x9a6/0x1ec0 io_uring/io_uring.c:2147
>        __do_sys_io_uring_enter+0xb85/0x1eb0 io_uring/io_uring.c:3087
>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>        do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>        entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> -> #0 (&u->lock/1){+.+.}-{2:2}:
>        check_prev_add kernel/locking/lockdep.c:3095 [inline]
>        check_prevs_add kernel/locking/lockdep.c:3214 [inline]
>        validate_chain kernel/locking/lockdep.c:3829 [inline]
>        __lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053
>        lock_acquire kernel/locking/lockdep.c:5665 [inline]
>        lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
>        _raw_spin_lock_nested+0x30/0x40 kernel/locking/spinlock.c:378
>        sk_diag_dump_icons net/unix/diag.c:87 [inline]
>        sk_diag_fill+0xaaf/0x10d0 net/unix/diag.c:155
>        sk_diag_dump net/unix/diag.c:193 [inline]
>        unix_diag_dump+0x3a9/0x640 net/unix/diag.c:217
>        netlink_dump+0x541/0xc20 net/netlink/af_netlink.c:2275
>        __netlink_dump_start+0x647/0x900 net/netlink/af_netlink.c:2380
>        netlink_dump_start include/linux/netlink.h:245 [inline]
>        unix_diag_handler_dump net/unix/diag.c:315 [inline]
>        unix_diag_handler_dump+0x5c2/0x830 net/unix/diag.c:304
>        __sock_diag_cmd net/core/sock_diag.c:235 [inline]
>        sock_diag_rcv_msg+0x31a/0x440 net/core/sock_diag.c:266
>        netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501
>        sock_diag_rcv+0x26/0x40 net/core/sock_diag.c:277
>        netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
>        netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
>        netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921
>        sock_sendmsg_nosec net/socket.c:714 [inline]
>        sock_sendmsg+0xcf/0x120 net/socket.c:734
>        sock_no_sendpage+0xff/0x140 net/core/sock.c:3162
>        kernel_sendpage.part.0+0x1d5/0x700 net/socket.c:3564
>        kernel_sendpage net/socket.c:3561 [inline]
>        sock_sendpage+0xdf/0x140 net/socket.c:1054
>        pipe_to_sendpage+0x2ad/0x380 fs/splice.c:364
>        splice_from_pipe_feed fs/splice.c:418 [inline]
>        __splice_from_pipe+0x43e/0x8a0 fs/splice.c:562
>        splice_from_pipe fs/splice.c:597 [inline]
>        generic_splice_sendpage+0xd4/0x140 fs/splice.c:746
>        do_splice_from fs/splice.c:767 [inline]
>        do_splice+0xb57/0x1920 fs/splice.c:1079
>        __do_splice+0x134/0x250 fs/splice.c:1144
>        __do_sys_splice fs/splice.c:1350 [inline]
>        __se_sys_splice fs/splice.c:1332 [inline]
>        __x64_sys_splice+0x198/0x250 fs/splice.c:1332
>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>        do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>        entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> other info that might help us debug this:
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(rlock-AF_UNIX);
>                                lock(&u->lock/1);
>                                lock(rlock-AF_UNIX);
>   lock(&u->lock/1);

This report seems false-positive.

sk_diag_dump_icons() works for TCP_LISTEN, so it won't
race with unix_dgram_sendmsg().

Also, sk_diag_dump_icons() does not seem to race with
unix_stream_connect().

- sk_diag_dump_icons
  - if (sk->sk_state == TCP_LISTEN)
    - spin_lock(&listener->sk_receive_queue.lock)
      - unix_state_lock_nested(req)

- unix_stream_connect
  - unix_state_unlock(listener)
    - spin_lock(&listener->sk_receive_queue.lock)



> 
>  *** DEADLOCK ***
> 
> 6 locks held by syz-executor.3/3509:
>  #0: ffff888074fac468 (&pipe->mutex/1){+.+.}-{3:3}, at: pipe_lock_nested fs/pipe.c:82 [inline]
>  #0: ffff888074fac468 (&pipe->mutex/1){+.+.}-{3:3}, at: pipe_lock+0x5a/0x70 fs/pipe.c:90
>  #1: ffffffff8d5aef88 (sock_diag_mutex){+.+.}-{3:3}, at: sock_diag_rcv+0x17/0x40 net/core/sock_diag.c:276
>  #2: ffffffff8d5af108 (sock_diag_table_mutex){+.+.}-{3:3}, at: __sock_diag_cmd net/core/sock_diag.c:230 [inline]
>  #2: ffffffff8d5af108 (sock_diag_table_mutex){+.+.}-{3:3}, at: sock_diag_rcv_msg+0x19b/0x440 net/core/sock_diag.c:266
>  #3: ffff88801d907678 (nlk_cb_mutex-SOCK_DIAG){+.+.}-{3:3}, at: netlink_dump+0xae/0xc20 net/netlink/af_netlink.c:2223
>  #4: ffff888046a7a798 (&net->unx.table.locks[i]){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:360 [inline]
>  #4: ffff888046a7a798 (&net->unx.table.locks[i]){+.+.}-{2:2}, at: unix_diag_dump+0x1b4/0x640 net/unix/diag.c:211
>  #5: ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:360 [inline]
>  #5: ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_dump_icons net/unix/diag.c:69 [inline]
>  #5: ffff8880765fe9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: sk_diag_fill+0x9c3/0x10d0 net/unix/diag.c:155
> 
> stack backtrace:
> CPU: 1 PID: 3509 Comm: syz-executor.3 Not tainted 5.19.0-rc4-next-20220628-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>  check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2175
>  check_prev_add kernel/locking/lockdep.c:3095 [inline]
>  check_prevs_add kernel/locking/lockdep.c:3214 [inline]
>  validate_chain kernel/locking/lockdep.c:3829 [inline]
>  __lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053
>  lock_acquire kernel/locking/lockdep.c:5665 [inline]
>  lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
>  _raw_spin_lock_nested+0x30/0x40 kernel/locking/spinlock.c:378
>  sk_diag_dump_icons net/unix/diag.c:87 [inline]
>  sk_diag_fill+0xaaf/0x10d0 net/unix/diag.c:155
>  sk_diag_dump net/unix/diag.c:193 [inline]
>  unix_diag_dump+0x3a9/0x640 net/unix/diag.c:217
>  netlink_dump+0x541/0xc20 net/netlink/af_netlink.c:2275
>  __netlink_dump_start+0x647/0x900 net/netlink/af_netlink.c:2380
>  netlink_dump_start include/linux/netlink.h:245 [inline]
>  unix_diag_handler_dump net/unix/diag.c:315 [inline]
>  unix_diag_handler_dump+0x5c2/0x830 net/unix/diag.c:304
>  __sock_diag_cmd net/core/sock_diag.c:235 [inline]
>  sock_diag_rcv_msg+0x31a/0x440 net/core/sock_diag.c:266
>  netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501
>  sock_diag_rcv+0x26/0x40 net/core/sock_diag.c:277
>  netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
>  netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
>  netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921
>  sock_sendmsg_nosec net/socket.c:714 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:734
>  sock_no_sendpage+0xff/0x140 net/core/sock.c:3162
>  kernel_sendpage.part.0+0x1d5/0x700 net/socket.c:3564
>  kernel_sendpage net/socket.c:3561 [inline]
>  sock_sendpage+0xdf/0x140 net/socket.c:1054
>  pipe_to_sendpage+0x2ad/0x380 fs/splice.c:364
>  splice_from_pipe_feed fs/splice.c:418 [inline]
>  __splice_from_pipe+0x43e/0x8a0 fs/splice.c:562
>  splice_from_pipe fs/splice.c:597 [inline]
>  generic_splice_sendpage+0xd4/0x140 fs/splice.c:746
>  do_splice_from fs/splice.c:767 [inline]
>  do_splice+0xb57/0x1920 fs/splice.c:1079
>  __do_splice+0x134/0x250 fs/splice.c:1144
>  __do_sys_splice fs/splice.c:1350 [inline]
>  __se_sys_splice fs/splice.c:1332 [inline]
>  __x64_sys_splice+0x198/0x250 fs/splice.c:1332
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x46/0xb0
> RIP: 0033:0x7f94a7089209
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f94a8105168 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
> RAX: ffffffffffffffda RBX: 00007f94a719bf60 RCX: 00007f94a7089209
> RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000003
> RBP: 00007f94a70e3161 R08: 0000000080000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007ffd5cb777cf R14: 00007f94a8105300 R15: 0000000000022000
>  </TASK>
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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