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Date:	Mon, 16 Jun 2014 11:24:43 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Toralf Förster <toralf.foerster@....de>
Cc:	Eric Paris <eparis@...hat.com>,
	Richard Weinberger <richard@....at>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 3.15: kernel BUG at kernel/auditsc.c:1525!

On Mon, Jun 16, 2014 at 11:21 AM, Toralf Förster <toralf.foerster@....de> wrote:
> On 06/16/2014 08:15 PM, Andy Lutomirski wrote:
>> On Mon, Jun 16, 2014 at 10:59 AM, Toralf Förster <toralf.foerster@....de> wrote:
>>> On 06/16/2014 07:50 PM, Andy Lutomirski wrote:
>>>> cc: eparis.  This might be a new audit bug.
>>>>
>>>> On Mon, Jun 16, 2014 at 10:36 AM, Toralf Förster <toralf.foerster@....de> wrote:
>>>>> On 06/16/2014 07:32 PM, Andy Lutomirski wrote:
>>>>>> On Mon, Jun 16, 2014 at 10:29 AM, Richard Weinberger <richard@....at> wrote:
>>>>>>> Am 16.06.2014 19:25, schrieb Andy Lutomirski:
>>>>>>>> On Mon, Jun 16, 2014 at 10:21 AM, Richard Weinberger
>>>>>>>> <richard.weinberger@...il.com> wrote:
>>>>>>>>> On Mon, Jun 16, 2014 at 6:33 PM, Toralf Förster <toralf.foerster@....de> wrote:
>>>>>>>>>> $ cat syscall.c
>>>>>>>>>> #include <unistd.h>
>>>>>>>>>> #include <sys/syscall.h>
>>>>>>>>>> int main(){return syscall(1000)!=-1;}
>>>>>>>>
>>>>>>>> What architecture are you building for?  On i386 and x86_64, 1000
>>>>>>>> shouldn't be big enough to trigger this.
>>>>>>>
>>>>>>> Toralf, is this an UML kernel?
>>>>>>>
>>>>>>
>>>>>> I'm also interested in the userspace architecture.  If it's x32
>>>>>> userspace, then I'm not surprised that there's a problem.
>>>>>
>>>>> It is a x86 system (ThinkPad T420) - not x32.
>>>>
>>>> I don't think this is CVE-2014-3917.  It looks like you're hitting this BUG:
>>>>
>>>> BUG_ON(context->in_syscall || context->name_count);
>>>>
>>>> Can you send the output of:
>>>>
>>>> auditctl -l [run as root]
>>>>
>>>> and
>>>>
>>>> dmesg |grep audit
>>>>
>>>> Are you using ptrace or anything like that (e.g. strace) when you
>>>> trigger this?  Are you using a funny glibc version?  Do you have
>>>> selinux or something like that enabled?
>>>>
>>>> --Andy
>>>>
>>> n22 ~ # auditctl -l
>>> LIST_RULES: exit,never arch=1073741827 (0x40000003) syscall=read,write,open,close,brk,fcntl,dup2,mmap,munmap,stat,fstat,nanosleep,rt_sigaction
>>>
>>>
>>> no ptrace/strace/SELinux, this is a stable x86 Gentoo Linux, glibc is 2.17, unstable are just KDE + Co.
>>>
>>> (@Richard: no. it is not an UML guest, I just stumbled over this while I tried to upgrade an unstable ~x86 Gentoo UML image using chroot)
>>>
>>> The trigger is just given by that C one-liner and kernel 3.15 (erm, I did not checked, if 3.14.x hit its too)
>>
>> At the very least, it looks like sysret_audit can result in invoking
>> the audit exit hook twice. That's not what's causing this, but it
>> still looks fishy.
>>
>> Toralf, can you run your test program under strace, post the output,
>> and see whether it still crashes?  There's some chance that strace
>> will "fix" it, since strace causes a different set of hooks to run.
>>
> tfoerste@n22 ~/tmp $ cat syscall.c
> #include <unistd.h>
> #include <sys/syscall.h>
> int main(){return syscall(1000)!=-1;}
>
> tfoerste@n22 ~/tmp $ gcc strcmp.c && strace ./a.out
> execve("./a.out", ["./a.out"], [/* 75 vars */]) = 0
> brk(0)                                  = 0x85f3000
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7750000
> access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
> open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
> fstat64(3, {st_mode=S_IFREG|0644, st_size=164108, ...}) = 0
> mmap2(NULL, 164108, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7727000
> close(3)                                = 0
> open("/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
> read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0 \316\1\0004\0\0\0"..., 512) = 512
> fstat64(3, {st_mode=S_IFREG|0755, st_size=1750448, ...}) = 0
> mmap2(NULL, 1759980, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7579000
> mmap2(0xb7721000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1a8000) = 0xb7721000
> mmap2(0xb7724000, 10988, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7724000
> close(3)                                = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7578000
> set_thread_area({entry_number:-1 -> 6, base_addr:0xb75786c0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
> mprotect(0xb7721000, 8192, PROT_READ)   = 0
> mprotect(0x8049000, 4096, PROT_READ)    = 0
> mprotect(0xb7774000, 4096, PROT_READ)   = 0
> munmap(0xb7727000, 164108)              = 0
> fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 5), ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb774f000
> write(1, "1\n", 21
> )                      = 2

Does this mean it didn't OOPS?  And where's the write(1, "1\n", 2)
coming from?  Are you sure you straced the right thing?

--Andy
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