Date:	Wed, 4 Feb 2015 14:06:48 -0500
From:	Trond Myklebust <trond.myklebust@...marydata.com>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	Nix <nix@...eri.org.uk>, "J. Bruce Fields" <bfields@...ldses.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [Patch] sunrpc: NULL utsname dereference on NFS umount during
 namespace cleanup

On Wed, Feb 4, 2015 at 12:08 PM, Bruno Prémont
<bonbons@...ux-vserver.org> wrote:
>
> On Fri, 30 January 2015 Trond Myklebust wrote:
> > On Sun, 2015-01-25 at 16:55 -0500, Trond Myklebust wrote:
> > > On Sun, Jan 25, 2015 at 4:06 PM, Bruno Prémont wrote:
> > > > On a system running home-brown container (mntns, utsns, pidns, netns)
> > > > with NFS mount-point bind-mounted into the container I hit the following
> > > > trace if nfs filesystem is first umount()ed in init ns and then later
> > > > umounted from container when the container exists.
> > > >
> > > > [51397.767310] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> > > > [51397.770671] IP: [<ffffffff81828173>] rpc_new_client+0x193/0x2b0
> > > > [51397.773967] PGD 0
> > > > [51397.777218] Oops: 0000 [#1] SMP
> > > > [51397.780490] Modules linked in:
> > > > [51397.783751] CPU: 0 PID: 1711 Comm: image-starter Not tainted 3.19.0-rc2-kvm+ #7
> > > > [51397.787123] Hardware name: Gigabyte Technology Co., Ltd. GA-A75M-UD2H/GA-A75M-UD2H, BIOS F6 09/28/2012
> > > > [51397.790606] task: ffff8800c9fcbac0 ti: ffff8801fe754000 task.ti: ffff8801fe754000
> > > > [51397.794149] RIP: 0010:[<ffffffff81828173>]  [<ffffffff81828173>] rpc_new_client+0x193/0x2b0
> > > > [51397.797798] RSP: 0018:ffff8801fe757908  EFLAGS: 00010246
> > > > [51397.801444] RAX: 0000000000000000 RBX: ffff88009dafb240 RCX: 0000000000000180
> > > > [51397.805174] RDX: 000000000000bae0 RSI: 0000000000001770 RDI: ffff88009dafb308
> > > > [51397.808913] RBP: ffff8801fe757948 R08: ffff88009daf92d8 R09: ffff88009dafb458
> > > > [51397.812673] R10: ffff88009dafb458 R11: ffff88020ec15bc0 R12: ffff8801fe757a40
> > > > [51397.816456] R13: ffffffff81b9d800 R14: ffff8800c6e31030 R15: 0000000000000000
> > > > [51397.820270] FS:  00007f335a3a1700(0000) GS:ffff88020ec00000(0000) knlGS:00000000f7287700
> > > > [51397.824168] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > > > [51397.828066] CR2: 0000000000000008 CR3: 00000001fc54d000 CR4: 00000000000007f0
> > > > [51397.832017] Stack:
> > > > [51397.835924]  000000000000000a ffffffff81b9d770 ffffffff81826450 ffff8801fe757a40
> > > > [51397.840023]  ffff8801fe757a40 ffff8800cf08d500 ffffffff81826450 ffffffff820f4728
> > > > [51397.844130]  ffff8801fe757978 ffffffff81828815 ffff8801fe757978 ffffffff8182aad8
> > > > [51397.848224] Call Trace:
> > > > [51397.852221]  [<ffffffff81826450>] ? call_start+0x20/0x20
> > > > [51397.856273]  [<ffffffff81826450>] ? call_start+0x20/0x20
> > > > [51397.860295]  [<ffffffff81828815>] rpc_create_xprt+0x15/0xb0
> > > > [51397.864324]  [<ffffffff8182aad8>] ? xprt_create_transport+0x108/0x1b0
> > > > [51397.868428]  [<ffffffff81828971>] rpc_create+0xc1/0x190
> > > > [51397.872574]  [<ffffffff81111c86>] ? internal_add_timer+0x66/0x80
> > > > [51397.876733]  [<ffffffff81113a99>] ? mod_timer+0x109/0x1e0
> > > > [51397.880877]  [<ffffffff8183a19e>] rpcb_create+0x6e/0x90
> > > > [51397.884999]  [<ffffffff8183a71a>] rpcb_getport_async+0x15a/0x330
> > > > [51397.889118]  [<ffffffff8182f1da>] ? rpc_malloc+0x3a/0x70
> > > > [51397.893240]  [<ffffffff811af8d2>] ? __kmalloc+0xc2/0x170
> > > > [51397.897354]  [<ffffffff81826830>] ? call_reserveresult+0x110/0x110
> > > > [51397.901490]  [<ffffffff81826450>] ? call_start+0x20/0x20
> > > > [51397.905606]  [<ffffffff81826450>] ? call_start+0x20/0x20
> > > > [51397.909662]  [<ffffffff8182648e>] call_bind+0x3e/0x40
> > > > [51397.913709]  [<ffffffff8182fa99>] __rpc_execute+0x79/0x330
> > > > [51397.917778]  [<ffffffff818327bd>] rpc_execute+0x5d/0xa0
> > > > [51397.921871]  [<ffffffff818286cb>] rpc_run_task+0x6b/0x90
> > > > [51397.925989]  [<ffffffff8182872e>] rpc_call_sync+0x3e/0xa0
> > > > [51397.930108]  [<ffffffff8127fe29>] nsm_mon_unmon+0xb9/0xd0
> > > > [51397.934191]  [<ffffffff8110e2a0>] ? call_rcu_bh+0x20/0x20
> > > > [51397.938235]  [<ffffffff8128018c>] nsm_unmonitor+0x8c/0x140
> > > > [51397.942309]  [<ffffffff8127bc43>] nlm_destroy_host_locked+0x63/0xa0
> > > > [51397.946442]  [<ffffffff8127c03c>] nlmclnt_release_host+0x7c/0x130
> > > > [51397.950591]  [<ffffffff81279645>] nlmclnt_done+0x15/0x30
> > > > [51397.954773]  [<ffffffff81241862>] nfs_destroy_server+0x12/0x20
> > > > [51397.958934]  [<ffffffff81242372>] nfs_free_server+0x22/0xa0
> > > > [51397.963053]  [<ffffffff8124cadd>] nfs_kill_super+0x1d/0x30
> > > > [51397.967158]  [<ffffffff811c2e2c>] deactivate_locked_super+0x4c/0x70
> > > > [51397.971286]  [<ffffffff811c33f9>] deactivate_super+0x49/0x70
> > > > [51397.975398]  [<ffffffff811ddafe>] cleanup_mnt+0x3e/0x90
> > > > [51397.979499]  [<ffffffff811ddb9d>] __cleanup_mnt+0xd/0x10
> > > > [51397.983598]  [<ffffffff810e04cc>] task_work_run+0xbc/0xe0
> > > > [51397.987697]  [<ffffffff810c8f95>] do_exit+0x295/0xaf0
> > > > [51397.991812]  [<ffffffff811c2239>] ? ____fput+0x9/0x10
> > > > [51397.995937]  [<ffffffff810e04b4>] ? task_work_run+0xa4/0xe0
> > > > [51398.000070]  [<ffffffff810c986a>] do_group_exit+0x3a/0xa0
> > > > [51398.004201]  [<ffffffff810c98df>] SyS_exit_group+0xf/0x10
> > > > [51398.008315]  [<ffffffff8185e8d2>] system_call_fastpath+0x12/0x17
> > > > [51398.012438] Code: 43 78 48 8d bb c8 00 00 00 48 89 7b 70 48 8b 30 e8 63 2d 01 00 c7 03 01 00 00 00 65 48 8b 04 25 00 aa 00 00 48 8b 80 c0 09 00 00 <4c> 8b 68 08 49 83 c5 45 4
> > > > [51398.022378] RIP  [<ffffffff81828173>] rpc_new_client+0x193/0x2b0
> > > > [51398.026732]  RSP <ffff8801fe757908>
> > > > [51398.031025] CR2: 0000000000000008
> > > > [51398.035326] ---[ end trace b701b037bc457620 ]---
> > > > [51398.058223] Fixing recursive fault but reboot is needed!
> > >
> > > We should rather change rpcb_create() to pass the nodename from the
> > > parent. The point is that the rpc_clnt->cl_nodename is used in various
> > > different contexts (for instance in the AUTH_SYS credential) where it
> > > isn't always appropriate to have it set to an empty string.
> >
> > I was rather hoping that Bruno would fix up his patch and resend, but
> > since other reports of the same bug are now surfacing... Please could
> > you all check if something like the following patch fixes it.
>
> This patch works for me, so
>   Tested-by: Bruno Prémont <bonbons@...ux-vserver.org>
>
> Now I get just the following complaint in dmesg on shutdown:
>   [ 1940.173201] lockd: cannot unmonitor nfs.home
>                                          ^^^^^^^^  name of NFS server
>
> This complaint did not happen with my "empty string" name
> patch.

Are there any clues from rpc.statd in your syslog that might help to
explain the error?

-- 
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@...marydata.com
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