On Tue, 11 Sep 2012 15:09:33 +0200
Bernd Schubert <bernd.schubert@xxxxxxxxxxx> wrote:
> Somehow one of my test VMs decided to start nfsd, which didn't work as
> it was not configured properly for that VM at all.
> But that resulted in a NULL pointer dereference:
>
> > 203.319525] svc: failed to register nfsdv2 RPC service (errno 111).
> > [ 203.320396] nfsd: last server has exited, flushing export cache
> > [ 203.320666] BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
> > [ 203.321132] IP: [<ffffffffa017c06e>] svc_destroy+0xe/0x120 [sunrpc]
> > [ 203.321430] PGD cfa0067 PUD 33ad1067 PMD 0
> > [ 203.321776] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
> > [ 203.322129] CPU 0
> > [ 203.322203] Modules linked in: ipv6 nfsd nfs lockd fscache auth_rpcgss nfs_acl sunrpc pcspkr 8250_pnp ext4 mbcache jbd2 crc16 crypto_hash crypto_algapi virtio_blk virtio_net ata_generic pata_acpi libata virtio_pci virtio_ring virtio scsi_mod unix [last unloaded: fhgfs_client_opentk]
> > [ 203.324013]
> > [ 203.324013] Pid: 1357, comm: rpc.nfsd Tainted: G O 3.5.3-debug #25 Bochs Bochs
> > [ 203.324013] RIP: 0010:[<ffffffffa017c06e>] [<ffffffffa017c06e>] svc_destroy+0xe/0x120 [sunrpc]
> > [ 203.324013] RSP: 0018:ffff880026ad3e08 EFLAGS: 00010292
> > [ 203.324013] RAX: 00000000ffffff91 RBX: ffff880026ae2008 RCX: 0000000000000100
> > [ 203.324013] RDX: 000000000000007f RSI: 0000000000000001 RDI: 0000000000000000
> > [ 203.324013] RBP: ffff880026ad3e18 R08: 0000000000000000 R09: 0000000000000000
> > [ 203.324013] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000004
> > [ 203.324013] R13: 0000000000000002 R14: ffff880028842680 R15: 00007fff03c6562c
> > [ 203.324013] FS: 00007f25f7dbe700(0000) GS:ffff88003de00000(0000) knlGS:0000000000000000
> > [ 203.324013] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > [ 203.324013] CR2: 0000000000000058 CR3: 0000000026b32000 CR4: 00000000000406f0
> > [ 203.324013] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [ 203.324013] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > [ 203.324013] Process rpc.nfsd (pid: 1357, threadinfo ffff880026ad2000, task ffff8800347f0000)
> > [ 203.324013] Stack:
> > [ 203.324013] ffff880026ae2008 ffff880026ae2008 ffff880026ad3e98 ffffffffa0272e3a
> > [ 203.324013] 2222222222222222 22222222ffffff91 2222222222220034 2222222222222222
> > [ 203.324013] ffff880026ad3e78 ffffffffa029c000 0000000000000000 0000000000000002
> > [ 203.324013] Call Trace:
> > [ 203.324013] [<ffffffffa0272e3a>] __write_ports+0xfa/0x260 [nfsd]
> > [ 203.324013] [<ffffffffa0272fde>] write_ports+0x3e/0x60 [nfsd]
> > [ 203.324013] [<ffffffffa0272fa0>] ? __write_ports+0x260/0x260 [nfsd]
> > [ 203.324013] [<ffffffffa02726f7>] nfsctl_transaction_write+0x57/0x90 [nfsd]
> > [ 203.324013] [<ffffffff811944fa>] vfs_write+0xca/0x170
> > [ 203.324013] [<ffffffff81194684>] sys_write+0x54/0x90
> > [ 203.324013] [<ffffffff814195a9>] system_call_fastpath+0x16/0x1b
> > [ 203.324013] Code: 03 83 10 01 00 00 4c 8b 64 24 08 48 8b 1c 24 c9 c3 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 53 48 83 ec 08 66 66 66 66 90 <8b> 47 58 48 89 fb 85 c0 74 14 83 e8 01 85 c0 89 47 58 74 1e e8
> > [ 203.324013] RIP [<ffffffffa017c06e>] svc_destroy+0xe/0x120 [sunrpc]
> > [ 203.324013] RSP <ffff880026ad3e08>
> > [ 203.324013] CR2: 0000000000000058
> > [ 203.337749] ---[ end trace 254f20c7dc1cafb9 ]---
>
>
> (gdb) l *(svc_destroy+0xe)
> 0xe06e is in svc_destroy (net/sunrpc/svc.c:544).
> 539 {
> 540 dprintk("svc: svc_destroy(%s, %d)\n",
> 541 serv->sv_program->pg_name,
> 542 serv->sv_nrthreads);
> 543
> 544 if (serv->sv_nrthreads) {
> 545 if (--(serv->sv_nrthreads) != 0) {
> 546 svc_sock_update_bufs(serv);
> 547 return;
> 548 }
>
>
> So 'serv' given as argument to svc_destroy() is NULL.
>
> gdb) l *(__write_ports+0xfa)
> 0x1e3a is in __write_ports (fs/nfsd/nfsctl.c:679).
> 674 err = svc_addsock(nfsd_serv, fd, buf,
> SIMPLE_TRANSACTION_LIMIT);
> 675 if (err < 0) {
> 676 if (nfsd_serv->sv_nrthreads == 1)
> 677 svc_shutdown_net(nfsd_serv, net);
> 678 svc_destroy(nfsd_serv);
> 679 return err;
> 680 }
> 681
> 682 /* Decrease the count, but don't shut down the service */
> 683 nfsd_serv->sv_nrthreads--;
>
> (Line 679 is in __write_ports_addfd() ).
>
> I'm not sure, but is there a svc_get() missing in nfsd_create_serv()?
>
>
> Cheers,
> Bernd
>
Hi Bernd,
Sorry for the late response. I just chased down a similar bug reported
against Fedora and noticed that you reported the same bug here. In
fact, there is not a missing svc_get() there since svc_create_pooled
returns a reference on success. The problem is likely that we're
calling svc_destroy(nfsd_serv) in the above code, but the pointer is
not getting NULL'ed out.
The good news is that I believe this is fixed in 3.6 kernels and up...
I have a bit more analysis here if you're interested:
https://bugzilla.redhat.com/show_bug.cgi?id=848867#c5
Cheers,
--
Jeff Layton <jlayton@xxxxxxxxxx>
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