Date:   Wed, 31 Aug 2016 15:37:37 -0400 (EDT)
From:   CAI Qian <caiqian@...hat.com>
To:     Rainer Weikusat <rweikusat@...ileactivedefense.com>,
        security@...nel.org
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        Eric Sandeen <esandeen@...hat.com>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: possible circular locking dependency detected (bisected)

Reverted the patch below fixes this problem.

c845acb324aa85a39650a14e7696982ceea75dc1
af_unix: Fix splice-bind deadlock

   CAI Qian

----- Original Message -----
> From: "CAI Qian" <caiqian@...hat.com>
> To: security@...nel.org
> Cc: "Miklos Szeredi" <mszeredi@...hat.com>, "Eric Sandeen" <esandeen@...hat.com>
> Sent: Tuesday, August 30, 2016 5:05:45 PM
> Subject: Re: possible circular locking dependency detected
> 
> FYI, this one can only be reproduced using the overlayfs docker backend.
> The device-mapper works fine. The XFS below has ftype=1.
> 
> # cp recvmsg01 /mnt
> # docker run -it -v /mnt/:/mnt/ rhel7 bash
> [root@...c99aedd93 /]# mount
> overlay on / type overlay
> (rw,relatime,seclabel,lowerdir=l/I5VXL74ENBNAEARZ4M2SIN3XD6:l/KZGBKPXLDXUGHYWMERFUBM4FRP,upperdir=9a7c1f735166b1f63d220b4b6c59cc37f3922719ef810c97182b814c1ab336df/diff,workdir=9a7c1f735166b1f63d220b4b6c59cc37f3922719ef810c97182b814c1ab336df/work)
> ...
> [root@...c99aedd93 /]# /mnt/recvmsg01
>     CAI Qian
> 
> ----- Original Message -----
> > From: "CAI Qian" <caiqian@...hat.com>
> > To: security@...nel.org
> > Sent: Friday, August 26, 2016 10:50:57 AM
> > Subject: possible circular locking dependency detected
> > 
> > FYI, just want to give a head up to see if there is anything obvious so
> > we can avoid a possible DoS somehow.
> > 
> > Running the LTP syscalls tests inside a container until this test trigger
> > below,
> > https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/recvmsg/recvmsg01.c
> > 
> > [ 4441.904103] open04 (42409) used greatest stack depth: 20552 bytes left
> > [ 4605.419167]
> > [ 4605.420831] ======================================================
> > [ 4605.427727] [ INFO: possible circular locking dependency detected ]
> > [ 4605.434720] 4.8.0-rc3+ #3 Not tainted
> > [ 4605.438803] -------------------------------------------------------
> > [ 4605.445796] recvmsg01/42878 is trying to acquire lock:
> > [ 4605.451528]  (sb_writers#8){.+.+.+}, at: [<ffffffff816a6d34>]
> > __sb_start_write+0xb4/0xf0
> > [ 4605.460642]
> > [ 4605.460642] but task is already holding lock:
> > [ 4605.467150]  (&u->readlock){+.+.+.}, at: [<ffffffff825242e9>]
> > unix_bind+0x299/0xdf0
> > [ 4605.475749]
> > [ 4605.475749] which lock already depends on the new lock.
> > [ 4605.475749]
> > [ 4605.484882]
> > [ 4605.484882] the existing dependency chain (in reverse order) is:
> > [ 4605.493234]
> > [ 4605.493234] -> #2 (&u->readlock){+.+.+.}:
> > [ 4605.497943]        [<ffffffff812b4b5a>] lock_acquire+0x1fa/0x440
> > [ 4605.504659]        [<ffffffff826948fd>]
> > mutex_lock_interruptible_nested+0xdd/0x920
> > [ 4605.513119]        [<ffffffff825242e9>] unix_bind+0x299/0xdf0
> > [ 4605.519540]        [<ffffffff821f6918>] SYSC_bind+0x1d8/0x240
> > [ 4605.525964]        [<ffffffff821fb6fe>] SyS_bind+0xe/0x10
> > [ 4605.531998]        [<ffffffff81007b56>] do_syscall_64+0x1a6/0x500
> > [ 4605.538811]        [<ffffffff8269e6bf>] return_from_SYSCALL_64+0x0/0x7a
> > [ 4605.546203]
> > [ 4605.546203] -> #1 (&type->i_mutex_dir_key#3/1){+.+.+.}:
> > [ 4605.552292]        [<ffffffff812b4b5a>] lock_acquire+0x1fa/0x440
> > [ 4605.559002]        [<ffffffff812a0f6e>] down_write_nested+0x5e/0xe0
> > [ 4605.566008]        [<ffffffff816d1b55>] filename_create+0x155/0x470
> > [ 4605.573013]        [<ffffffff816d403f>] SyS_mkdir+0xaf/0x1f0
> > [ 4605.579339]        [<ffffffff8269e5fc>]
> > entry_SYSCALL_64_fastpath+0x1f/0xbd
> > [ 4605.587119]
> > [ 4605.587119] -> #0 (sb_writers#8){.+.+.+}:
> > [ 4605.591835]        [<ffffffff812b31f3>] __lock_acquire+0x3043/0x3dd0
> > [ 4605.598935]        [<ffffffff812b4b5a>] lock_acquire+0x1fa/0x440
> > [ 4605.605646]        [<ffffffff812a138f>] percpu_down_read+0x4f/0xa0
> > [ 4605.612552]        [<ffffffff816a6d34>] __sb_start_write+0xb4/0xf0
> > [ 4605.619459]        [<ffffffff817050d1>] mnt_want_write+0x41/0xb0
> > [ 4605.626173]        [<ffffffffa0ce4be6>] ovl_want_write+0x76/0xa0
> > [overlay]
> > [ 4605.633860]        [<ffffffffa0cebd63>] ovl_create_object+0xa3/0x2d0
> > [overlay]
> > [ 4605.641942]        [<ffffffffa0cebfc1>] ovl_mknod+0x31/0x40 [overlay]
> > [ 4605.649138]        [<ffffffff816c16db>] vfs_mknod+0x34b/0x560
> > [ 4605.655570]        [<ffffffff8252451a>] unix_bind+0x4ca/0xdf0
> > [ 4605.661991]        [<ffffffff821f6918>] SYSC_bind+0x1d8/0x240
> > [ 4605.668412]        [<ffffffff821fb6fe>] SyS_bind+0xe/0x10
> > [ 4605.674456]        [<ffffffff81007b56>] do_syscall_64+0x1a6/0x500
> > [ 4605.681266]        [<ffffffff8269e6bf>] return_from_SYSCALL_64+0x0/0x7a
> > [ 4605.688657]
> > [ 4605.688657] other info that might help us debug this:
> > [ 4605.688657]
> > [ 4605.697590] Chain exists of:
> > [ 4605.697590]   sb_writers#8 --> &type->i_mutex_dir_key#3/1 -->
> > &u->readlock
> > [ 4605.697590]
> > [ 4605.707287]  Possible unsafe locking scenario:
> > [ 4605.707287]
> > [ 4605.713890]        CPU0                    CPU1
> > [ 4605.718943]        ----                    ----
> > [ 4605.723995]   lock(&u->readlock);
> > [ 4605.727708]
> > lock(&type->i_mutex_dir_key#3/1);
> > [ 4605.735613]                                lock(&u->readlock);
> > [ 4605.742146]   lock(sb_writers#8);
> > [ 4605.745880]
> > [ 4605.745880]  *** DEADLOCK ***
> > [ 4605.745880]
> > [ 4605.752486] 3 locks held by recvmsg01/42878:
> > [ 4605.757247]  #0:  (sb_writers#13){.+.+.+}, at: [<ffffffff816a6d34>]
> > __sb_start_write+0xb4/0xf0
> > [ 4605.766930]  #1:  (&sb->s_type->i_mutex_key#16/1){+.+.+.}, at:
> > [<ffffffff816d1b55>] filename_create+0x155/0x470
> > [ 4605.778269]  #2:  (&u->readlock){+.+.+.}, at: [<ffffffff825242e9>]
> > unix_bind+0x299/0xdf0
> > [ 4605.787350]
> > [ 4605.787350] stack backtrace:
> > [ 4605.792213] CPU: 38 PID: 42878 Comm: recvmsg01 Not tainted 4.8.0-rc3+ #3
> > [ 4605.799691] Hardware name: Intel Corporation S2600WTT/S2600WTT, BIOS
> > GRNDSDP1.86B.0044.R00.1501191641 01/19/2015
> > [ 4605.811047]  0000000000000000 000000009cc8af78 ffff8803c2c37770
> > ffffffff81a63fb1
> > [ 4605.819341]  ffffffff842a0590 ffffffff842c0ae0 ffff8803c2c377c0
> > ffffffff812ac0d6
> > [ 4605.827633]  ffffffff842a0590 ffff8804619f0d08 ffff8803c2c378e0
> > ffff8804619f0d08
> > [ 4605.835927] Call Trace:
> > [ 4605.838656]  [<ffffffff81a63fb1>] dump_stack+0x85/0xc4
> > [ 4605.844390]  [<ffffffff812ac0d6>] print_circular_bug+0x356/0x460
> > [ 4605.851092]  [<ffffffff812b31f3>] __lock_acquire+0x3043/0x3dd0
> > [ 4605.857602]  [<ffffffff81632710>] ? kfree+0x310/0x370
> > [ 4605.863238]  [<ffffffff812b01b0>] ?
> > debug_check_no_locks_freed+0x2c0/0x2c0
> > [ 4605.870912]  [<ffffffff818be5f2>] ? avc_has_perm+0xa2/0x480
> > [ 4605.877130]  [<ffffffff818be792>] ? avc_has_perm+0x242/0x480
> > [ 4605.883443]  [<ffffffff818be7b1>] ? avc_has_perm+0x261/0x480
> > [ 4605.889758]  [<ffffffff818be5f2>] ? avc_has_perm+0xa2/0x480
> > [ 4605.895977]  [<ffffffff812b4b5a>] lock_acquire+0x1fa/0x440
> > [ 4605.902098]  [<ffffffff816a6d34>] ? __sb_start_write+0xb4/0xf0
> > [ 4605.908607]  [<ffffffff812a138f>] percpu_down_read+0x4f/0xa0
> > [ 4605.914921]  [<ffffffff816a6d34>] ? __sb_start_write+0xb4/0xf0
> > [ 4605.921429]  [<ffffffff816a6d34>] __sb_start_write+0xb4/0xf0
> > [ 4605.927742]  [<ffffffff817050d1>] mnt_want_write+0x41/0xb0
> > [ 4605.933875]  [<ffffffffa0ce4be6>] ovl_want_write+0x76/0xa0 [overlay]
> > [ 4605.940967]  [<ffffffffa0cebd63>] ovl_create_object+0xa3/0x2d0 [overlay]
> > [ 4605.948445]  [<ffffffffa0cebcc0>] ?
> > ovl_create_or_link.part.3+0xc70/0xc70
> > [overlay]
> > [ 4605.956990]  [<ffffffff818c55c2>] ? selinux_inode_mknod+0x42/0x80
> > [ 4605.963790]  [<ffffffffa0cebfc1>] ovl_mknod+0x31/0x40 [overlay]
> > [ 4605.970395]  [<ffffffff816c16db>] vfs_mknod+0x34b/0x560
> > [ 4605.976224]  [<ffffffff8252451a>] unix_bind+0x4ca/0xdf0
> > [ 4605.982053]  [<ffffffff82524050>] ? unix_autobind.isra.24+0x600/0x600
> > [ 4605.989244]  [<ffffffff815a7d86>] ? __might_fault+0xf6/0x1b0
> > [ 4605.995550]  [<ffffffff821f6918>] SYSC_bind+0x1d8/0x240
> > [ 4606.001381]  [<ffffffff821f6740>] ?
> > move_addr_to_kernel.part.13+0xe0/0xe0
> > [ 4606.008958]  [<ffffffff813d1af5>] ? __audit_syscall_entry+0x325/0x6f0
> > [ 4606.016144]  [<ffffffff813d1af5>] ? __audit_syscall_entry+0x325/0x6f0
> > [ 4606.023332]  [<ffffffff81007a02>] ? do_syscall_64+0x52/0x500
> > [ 4606.029645]  [<ffffffff821fb6f0>] ? SyS_socketpair+0x470/0x470
> > [ 4606.036154]  [<ffffffff821fb6fe>] SyS_bind+0xe/0x10
> > [ 4606.041595]  [<ffffffff81007b56>] do_syscall_64+0x1a6/0x500
> > [ 4606.047813]  [<ffffffff8100401a>] ? trace_hardirqs_on_thunk+0x1a/0x1c
> > [ 4606.055000]  [<ffffffff8269e6bf>] entry_SYSCALL64_slow_path+0x25/0x25

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