tun oops dereferencing garbage nsproxy-> address.

[Dave Jones]

BUG: unable to handle kernel paging request at 0000000100000029
IP: [<ffffffffa06ec54f>] tun_chr_open+0x4f/0x80 [tun]
PGD 5ae4f067 PUD 0 
Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
CPU 1 
Modules linked in: tun binfmt_misc can_bcm cmtp kernelcapi nfnetlink bnep can_raw af_802154 phonet bluetooth can pppoe pppox ppp_generic slhc irda crc_ccitt rds af_key rose ax25 appletalk atm ipx p8022 psnap llc p8023 tcp_lp iwlwifi mac80211 cfg80211 nfs fscache auth_rpcgss nfs_acl fuse lockd ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack xts gf128mul dm_crypt dm_mirror dm_region_hash dm_log arc4 snd_hda_codec_hdmi uvcvideo snd_hda_codec_idt videobuf2_core snd_usb_audio snd_hda_intel videodev snd_hda_codec dell_wmi sparse_keymap media snd_usbmidi_lib snd_hwdep v4l2_compat_ioctl32 snd_rawmidi cdc_ether videobuf2_vmalloc videobuf2_memops snd_seq usbnet cdc_wdm mii cdc_acm snd_seq_device snd_pcm dell_laptop dcdbas joydev microcode snd_timer tg3 snd pcspkr i2c_i801 iTCO_wdt iTCO_vendor_support soundcore snd_page_alloc rfkill wmi sunrpc i915 drm_kms_helper drm i2c_algo_bit i2c_core video [last unloaded: cfg80211]

Pid: 15413, comm: trinity Not tainted 3.3.0-rc7+ #54 Dell Inc. Adamo 13   /0N70T0
RIP: 0010:[<ffffffffa06ec54f>]  [<ffffffffa06ec54f>] tun_chr_open+0x4f/0x80 [tun]
RSP: 0018:ffff8800a5e29bc8  EFLAGS: 00010286
RAX: ffff88012036fd88 RBX: ffff8801084c4dc0 RCX: 0000000000000006
RDX: 0000000100000001 RSI: ffff88000fd9abc8 RDI: 0000000000000292
RBP: ffff8800a5e29bd8 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801084c4dc0
R13: ffff88012eb10d20 R14: ffffffffa06f0000 R15: ffffffff81856ae0
FS:  00007f3ebcb1a700(0000) GS:ffff88013b400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100000029 CR3: 00000000032bb000 CR4: 00000000000406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process trinity (pid: 15413, threadinfo ffff8800a5e28000, task ffff88000fd9a4a0)
Stack:
 00000000000000c8 0000000000000000 ffff8800a5e29c38 ffffffff813fcf38
 ffffffff81c54838 0000000000000001 ffff8800a5e29c18 ffffffff816a1afd
 ffff8801084c4dc0 ffff8801396bbab8 ffff88012eb10d20 0000000000000000
Call Trace:
 [<ffffffff813fcf38>] misc_open+0x1d8/0x670
 [<ffffffff816a1afd>] ? sub_preempt_count+0x9d/0xd0
 [<ffffffff811c2978>] chrdev_open+0x258/0x350
 [<ffffffff811baa04>] __dentry_open+0x384/0x550
 [<ffffffff816a1afd>] ? sub_preempt_count+0x9d/0xd0
 [<ffffffff811c2720>] ? cdev_put+0x30/0x30
 [<ffffffff811bc224>] nameidata_to_filp+0x74/0x80
 [<ffffffff811ce59c>] do_last+0x26c/0x930
 [<ffffffff811ced76>] path_openat+0xd6/0x3e0
 [<ffffffff810a6298>] ? sched_clock_cpu+0xb8/0x130
 [<ffffffff811cf1a2>] do_filp_open+0x42/0xa0
 [<ffffffff8169d845>] ? _raw_spin_unlock+0x35/0x60
 [<ffffffff811dd7cd>] ? alloc_fd+0x18d/0x210
 [<ffffffff811bc328>] do_sys_open+0xf8/0x1d0
 [<ffffffff810faadc>] ? __audit_syscall_entry+0xcc/0x310
 [<ffffffff811bc421>] sys_open+0x21/0x30
 [<ffffffff816a5a69>] system_call_fastpath+0x16/0x1b
Code: 00 00 00 e8 64 8d ab e0 48 85 c0 74 46 c7 00 00 00 00 00 48 c7 40 08 00 00 00 00 65 48 8b 14 25 00 c9 00 00 48 8b 92 50 05 00 00 <48> 8b 52 28 f0 ff 42 04 48 89 50 10 48 89 83 28 01 00 00 31 c0 
RIP  [<ffffffffa06ec54f>] tun_chr_open+0x4f/0x80 [tun]
 RSP <ffff8800a5e29bc8>
CR2: 0000000100000029
Disabling lock debugging due to kernel taint
---[ end trace 9e00e91b0629ad80 ]---


oops happened here..

        tfile->net = get_net(current->nsproxy->net_ns);
     548:       48 8b 92 50 05 00 00    mov    0x550(%rdx),%rdx
     54f:       48 8b 52 28             mov    0x28(%rdx),%rdx

My guess is the fuzzer called some syscall that set current->nsproxy
to garbage (0x0000000100000001), which later got dereferenced when it
subsequently randomly did an open() on tun.

Any thoughts ?

	Dave

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