Message-Id: <201203222029.27595.maciej.rutecki@gmail.com>
Date:	Thu, 22 Mar 2012 20:29:27 +0100
From:	Maciej Rutecki <maciej.rutecki@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Dave Jones <davej@...hat.com>, netdev@...r.kernel.org,
	Linux Kernel <linux-kernel@...r.kernel.org>, serue@...ibm.com
Subject: Re: tun oops dereferencing garbage nsproxy-> address.

On czwartek, 22 marca 2012 o 04:58:58 Eric W. Biederman wrote:
> Maciej Rutecki <maciej.rutecki@...il.com> writes:
> > On wtorek, 13 marca 2012 o 04:42:02 Dave Jones wrote:
> >> 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
> > 
> > I created a Bugzilla entry at
> > https://bugzilla.kernel.org/show_bug.cgi?id=42960
> > for your bug/regression report, please add your address to the CC list in
> > there, thanks!
> 
> There is not enough information here to track this as any kind of bug to
> be fixed.   This problem can be neither reproduced nor is it a
> direct consequence of anything obvious in the code.  The bug should
> simply be closed with "can not reproduce".  There is no evidence
> that this is any kind of regression.
> 
> If there is a system to track weird failures and note strange
> occurrences and to start looking for patterns this might be interesting,
> but I don't believe that system is the kernel bugzilla system.
> 
> This was all covered in the discussion of this issue before you put it
> in the kernel bugzilla so I don't understand why you bothered.  There is
> simply too little information to do anything interesting with this
> failure.  Most likely this is the result of a kernel memory stomp
> triggered by an unprivileged process.
> 
> I think such memory stomps suck but there is not enough information in
> this thread to really even start looking and there is a lot of kernel
> code to look through.  You don't seem to be interested in digging into
> this yourself so adding this to bugzilla simply appears to be a waste
> of time.
> 
> Eric

Ok. Closed

Regards
-- 
Maciej Rutecki
http://www.mrutecki.pl
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