Re: 3.15: kernel BUG at kernel/auditsc.c:1525!

Toralf Förster
2014-06-20T17:35:40Z

On 06/20/2014 05:41 PM, Andy Lutomirski wrote:
> On Mon, Jun 16, 2014 at 2:48 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 06/16/2014 02:35 PM, Andy Lutomirski wrote:
>>>
>>> To hpa, etc: It appears that entry_32.S is missing any call to the
>>> audit exit hook on the badsys path. If I'm diagnosing this bug report
>>> correctly, this causes OOPSes.
>>>
>>> The the world at large: it's increasingly apparent that no one (except
>>> maybe the blackhats) has ever scrutinized the syscall auditing code.
>>> This is two old severe bugs in the code that have probably been there
>>> for a long time.
>>>
>>
>> Yes, the audit code is a total mess.
>>
>>> The bad syscall nr paths are their own incomprehensible route
>>> through the entry control flow. Rearrange them to work just like
>>> syscalls that return -ENOSYS.
>>
>> I have to admit... it sort of lends itself to a solution like this:
>>
>> /* For the 64-bit case, analogous code for 32 bits */
>> movl $__NR_syscall_max+1,%ecx # *Not* __NR_syscall_max
>> cmpq %rcx,%rax
>> cmovae %rcx,%rax
>> movq %r10,%rcx
>> call *sys_call_table(,%rax,8)
>>
>> ... and having an extra (invalid) system call slot in the syscall table
>> beyond the end instead of branching off separately.
>>
>> (Note: we could use either cmova or cmovae, and either the 32- or 64-bit
>> form... the reason why is left as an exercise to the reader.)
>
> This is CVE-2014-4508, and it's probably worth fixing.
>
> Is my patch good? I can resent and cc stable if needed.
>
> --Andy
>
I'm running my system since the time you sent it to me w/o any problems with that patch on top of 3.15.1 :

tfoerste@n22 ~/devel/linux $ cat ~/devel/priv/0001-x86_32-entry-Fix-badsys-paths.patch

>From 8b43bd2118d876cb3163e8f7d9cd8253da649335 Mon Sep 17 00:00:00 2001
Message-Id: <8b43bd2118d876cb3163e8f7d9cd8253da649335.1402954406.git.luto@amacapital.net>
From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 16 Jun 2014 14:28:19 -0700
Subject: [PATCH] x86_32,entry: Fix badsys paths
MIME-Version: 1.0
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The bad syscall nr paths are their own incomprehensible route
through the entry control flow. Rearrange them to work just like
syscalls that return -ENOSYS.

This should fix an OOPS in the audit code when auditing is enabled
and bad syscall nrs are used.

Reported-by: Toralf Förster <toralf.foerster@gmx.de>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
---

--
Toralf