Subject: Re: tun oops dereferencing garbage nsproxy-> address.

From: [email-masked] (Eric W. Biederman)
Date: Tue, 13 Mar 2012 11:19:40 -0700

Dave Jones <[email-masked]> writes:

> 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 dcdb
 as 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 ?

It smells like a memory stomp.  current->nsproxy is always supposed to
have a valid value, and it never would have an odd value.  The value
should always be at least 8 byte aligned.

Since the value is impossible this doesn't feel like a path where the
error handling is wrong.

So I am guessing this is a memory stomp.  My guess it would take the
same sequence of system calls on the same kernel build to reproduce
this problem in the same place.

Do you have any more information?

Eric