Re: file access causes a kernel bug

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On 01/29/2014 11:58 AM, Matthew Thode wrote:
> On 01/29/2014 08:17 AM, Stephen Smalley wrote:
>> On 01/29/2014 09:07 AM, Stephen Smalley wrote:
>>> On 01/29/2014 08:55 AM, Paul Moore wrote:
>>>> On Wednesday, January 29, 2014 02:11:45 AM Matthew Thode wrote:
>>>>> On 01/29/2014 02:04 AM, Matthew Thode wrote:
>>>>>> This happens consistantly, just ls a particular dir and wheeeeee.
>>>>>>
>>>>>> [  473.893141] ------------[ cut here ]------------
>>>>>> [  473.962110] kernel BUG at security/selinux/ss/services.c:654!
>>>>>> [  473.995314] invalid opcode: 0000 [#6] SMP
>>>>>> [  474.027196] Modules linked in:
>>>>>> [  474.058118] CPU: 0 PID: 8138 Comm: ls Tainted: G      D   I
>>>>>> 3.13.0-grsec #1
>>>>>> [  474.116637] Hardware name: Supermicro X8ST3/X8ST3, BIOS 2.0
>>>>>> 07/29/10
>>>>>> [  474.149768] task: ffff8805f50cd010 ti: ffff8805f50cd488 task.ti:
>>>>>> ffff8805f50cd488
>>>>>> [  474.183707] RIP: 0010:[<ffffffff814681c7>]  [<ffffffff814681c7>]
>>>>>> context_struct_compute_av+0xce/0x308
>>>>>> [  474.219954] RSP: 0018:ffff8805c0ac3c38  EFLAGS: 00010246
>>>>>> [  474.252253] RAX: 0000000000000000 RBX: ffff8805c0ac3d94 RCX:
>>>>>> 0000000000000100
>>>>>> [  474.287018] RDX: ffff8805e8aac000 RSI: 00000000ffffffff RDI:
>>>>>> ffff8805e8aaa000
>>>>>> [  474.321199] RBP: ffff8805c0ac3cb8 R08: 0000000000000010 R09:
>>>>>> 0000000000000006
>>>>>> [  474.357446] R10: 0000000000000000 R11: ffff8805c567a000 R12:
>>>>>> 0000000000000006
>>>>>> [  474.419191] R13: ffff8805c2b74e88 R14: 00000000000001da R15:
>>>>>> 0000000000000000
>>>>>> [  474.453816] FS:  00007f2e75220800(0000) GS:ffff88061fc00000(0000)
>>>>>> knlGS:0000000000000000
>>>>>> [  474.489254] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>> [  474.522215] CR2: 00007f2e74716090 CR3: 00000005c085e000 CR4:
>>>>>> 00000000000207f0
>>>>>> [  474.556058] Stack:
>>>>>> [  474.584325]  ffff8805c0ac3c98 ffffffff811b549b ffff8805c0ac3c98
>>>>>> ffff8805f1190a40
>>>>>> [  474.618913]  ffff8805a6202f08 ffff8805c2b74e88 00068800d0464990
>>>>>> ffff8805e8aac860
>>>>>> [  474.653955]  ffff8805c0ac3cb8 000700068113833a ffff880606c75060
>>>>>> ffff8805c0ac3d94
>>>>>> [  474.690461] Call Trace:
>>>>>> [  474.723779]  [<ffffffff811b549b>] ? lookup_fast+0x1cd/0x22a
>>>>>> [  474.778049]  [<ffffffff81468824>] security_compute_av+0xf4/0x20b
>>>>>> [  474.811398]  [<ffffffff8196f419>] avc_compute_av+0x2a/0x179
>>>>>> [  474.843813]  [<ffffffff8145727b>] avc_has_perm+0x45/0xf4
>>>>>> [  474.875694]  [<ffffffff81457d0e>] inode_has_perm+0x2a/0x31
>>>>>> [  474.907370]  [<ffffffff81457e76>] selinux_inode_getattr+0x3c/0x3e
>>>>>> [  474.938726]  [<ffffffff81455cf6>] security_inode_getattr+0x1b/0x22
>>>>>> [  474.970036]  [<ffffffff811b057d>] vfs_getattr+0x19/0x2d
>>>>>> [  475.000618]  [<ffffffff811b05e5>] vfs_fstatat+0x54/0x91
>>>>>> [  475.030402]  [<ffffffff811b063b>] vfs_lstat+0x19/0x1b
>>>>>> [  475.061097]  [<ffffffff811b077e>] SyS_newlstat+0x15/0x30
>>>>>> [  475.094595]  [<ffffffff8113c5c1>] ? __audit_syscall_entry+0xa1/0xc3
>>>>>> [  475.148405]  [<ffffffff8197791e>] system_call_fastpath+0x16/0x1b
>>>>>> [  475.179201] Code: 00 48 85 c0 48 89 45 b8 75 02 0f 0b 48 8b 45 a0 48
>>>>>> 8b 3d 45 d0 b6 00 8b 40 08 89 c6 ff ce e8 d1 b0 06 00 48 85 c0 49 89 c7
>>>>>> 75 02 <0f> 0b 48 8b 45 b8 4c 8b 28 eb 1e 49 8d 7d 08 be 80 01 00 00 e8
>>>>>> [  475.255884] RIP  [<ffffffff814681c7>]
>>>>>> context_struct_compute_av+0xce/0x308
>>>>>> [  475.296120]  RSP <ffff8805c0ac3c38>
>>>>>> [  475.328734] ---[ end trace f076482e9d754adc ]---
>>>>>>
>>>>>
>>>>> sorry, forgot to add, this is for 3.13.0 as well.
>>>>>
>>>>> ls ./.config/ipython/profile_default/
>>>>> Segmentation fault
>>>>
>>>> Thanks for passing this along, but can you elaborate a bit more on this?  
>>>> Distribution?  Kernel package?  SELinux policy?  Any unusual configuration?  
>>>> etc.
>>>>
>>>> I ask because I'm not seeing this problem on my system and it seems like a 
>>>> fairly basic thing to be broken; if there was an issue with 'ls' on 3.13 I 
>>>> expect we would be flooded with angry users right now ...
>>>
>>> Does it happen on any filesystem other than ZFS?
>>>
>>> Do you have any prior SELinux output leading up to this bug?
>>
>> Also, what policy are you using and what is the security context on that
>> file?
>>
> Ok, one at a time :D
> 
> I'm on gentoo using the strict policy (in permissive for now...)
> 
> Kernel is 3.13 (zfs is built from git head as of 2014-01-26 (selinux
> patches went in :D))
> 
> using basepol 2.20130424
> 
> No unusual config that I can think of.  I've found multiple files that
> this happens with).
> 
> Only on zfs that I can see
> 
> Dunno what you mean by prior selinux output, just some random selinux
> denials because restorecon -RF fails because of this.
> 
> I can't see either the file name or the context of that file.  As soon
> as anything tries to access anything about the file I get that backtrace.

Looking at the code in question, I don't see any way to reach that BUG
without memory corruption in the kernel.  Which could just as easily be
in ZFS as anything else...


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