Date:   Mon, 1 Feb 2021 14:37:28 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     syzbot <syzbot+2ae0ca9d7737ad1a62b7@...kaller.appspotmail.com>
Cc:     akpm@...ux-foundation.org, davem@...emloft.net, hagen@...u.net,
        johannes@...solutions.net, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, sfr@...b.auug.org.au,
        syzkaller-bugs@...glegroups.com
Subject: Re: possible deadlock in cfg80211_netdev_notifier_call

On Mon, Feb 01, 2021 at 01:17:13AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    b01f250d Add linux-next specific files for 20210129
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14daa408d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=725bc96dc234fda7
> dashboard link: https://syzkaller.appspot.com/bug?extid=2ae0ca9d7737ad1a62b7
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1757f2a0d00000
> 
> The issue was bisected to:
> 
> commit cc9327f3b085ba5be5639a5ec3ce5b08a0f14a7c
> Author: Mike Rapoport <rppt@...ux.ibm.com>
> Date:   Thu Jan 28 07:42:40 2021 +0000
> 
>     mm: introduce memfd_secret system call to create "secret" memory areas
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1505d28cd00000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=1705d28cd00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1305d28cd00000

Sounds really weird to me. At this point the memfd_secret syscall is not
even wired to arch syscall handlers. I cannot see how it can be a reason of
deadlock in wireless...
 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2ae0ca9d7737ad1a62b7@...kaller.appspotmail.com
> Fixes: cc9327f3b085 ("mm: introduce memfd_secret system call to create "secret" memory areas")
> 
> ============================================
> WARNING: possible recursive locking detected
> 5.11.0-rc5-next-20210129-syzkaller #0 Not tainted
> --------------------------------------------
> syz-executor.1/27924 is trying to acquire lock:
> ffff88801c7305e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: wiphy_lock include/net/cfg80211.h:5267 [inline]
> ffff88801c7305e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: cfg80211_netdev_notifier_call+0x68c/0x1180 net/wireless/core.c:1407
> 
> but task is already holding lock:
> ffff88801c7305e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: wiphy_lock include/net/cfg80211.h:5267 [inline]
> ffff88801c7305e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: nl80211_pre_doit+0x347/0x5a0 net/wireless/nl80211.c:14837
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(&rdev->wiphy.mtx);
>   lock(&rdev->wiphy.mtx);
> 
>  *** DEADLOCK ***
> 
>  May be due to missing lock nesting notation
> 
> 3 locks held by syz-executor.1/27924:
>  #0: ffffffff8cd04eb0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40 net/netlink/genetlink.c:810
>  #1: ffffffff8cc75248 (rtnl_mutex){+.+.}-{3:3}, at: nl80211_pre_doit+0x22/0x5a0 net/wireless/nl80211.c:14793
>  #2: ffff88801c7305e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: wiphy_lock include/net/cfg80211.h:5267 [inline]
>  #2: ffff88801c7305e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: nl80211_pre_doit+0x347/0x5a0 net/wireless/nl80211.c:14837
> 
> stack backtrace:
> CPU: 1 PID: 27924 Comm: syz-executor.1 Not tainted 5.11.0-rc5-next-20210129-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:2829 [inline]
>  check_deadlock kernel/locking/lockdep.c:2872 [inline]
>  validate_chain kernel/locking/lockdep.c:3661 [inline]
>  __lock_acquire.cold+0x14c/0x3b4 kernel/locking/lockdep.c:4899
>  lock_acquire kernel/locking/lockdep.c:5509 [inline]
>  lock_acquire+0x1a8/0x720 kernel/locking/lockdep.c:5474
>  __mutex_lock_common kernel/locking/mutex.c:956 [inline]
>  __mutex_lock+0x134/0x1110 kernel/locking/mutex.c:1103
>  wiphy_lock include/net/cfg80211.h:5267 [inline]
>  cfg80211_netdev_notifier_call+0x68c/0x1180 net/wireless/core.c:1407
>  notifier_call_chain+0xb5/0x200 kernel/notifier.c:83
>  call_netdevice_notifiers_info+0xb5/0x130 net/core/dev.c:2040
>  call_netdevice_notifiers_extack net/core/dev.c:2052 [inline]
>  call_netdevice_notifiers net/core/dev.c:2066 [inline]
>  unregister_netdevice_many+0x943/0x1750 net/core/dev.c:10704
>  unregister_netdevice_queue+0x2dd/0x3c0 net/core/dev.c:10638
>  register_netdevice+0x109f/0x14a0 net/core/dev.c:10013
>  cfg80211_register_netdevice+0x11d/0x2a0 net/wireless/core.c:1349
>  ieee80211_if_add+0xfb8/0x18f0 net/mac80211/iface.c:1990
>  ieee80211_add_iface+0x99/0x160 net/mac80211/cfg.c:125
>  rdev_add_virtual_intf net/wireless/rdev-ops.h:45 [inline]
>  nl80211_new_interface+0x541/0x1100 net/wireless/nl80211.c:3977
>  genl_family_rcv_msg_doit+0x228/0x320 net/netlink/genetlink.c:739
>  genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
>  genl_rcv_msg+0x328/0x580 net/netlink/genetlink.c:800
>  netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
>  genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
>  netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
>  netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
>  netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
>  sock_sendmsg_nosec net/socket.c:654 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:674
>  ____sys_sendmsg+0x6e8/0x810 net/socket.c:2350
>  ___sys_sendmsg+0xf3/0x170 net/socket.c:2404
>  __sys_sendmsg+0xe5/0x1b0 net/socket.c:2437
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x45e219
> Code: 0d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 db b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f5dce348c68 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045e219
> RDX: 0000000000000000 RSI: 0000000020000400 RDI: 0000000000000004
> RBP: 000000000119c110 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000119c0dc
> R13: 00007ffdf00f97ff R14: 00007f5dce3499c0 R15: 000000000119c0dc
> 
> 
> ---
> 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.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches

-- 
Sincerely yours,
Mike.

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