From: takahiro.akashi@linaro.org (AKASHI Takahiro)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations
Date: Tue, 29 Jul 2014 15:49:47 +0900 [thread overview]
Message-ID: <53D7440B.10006@linaro.org> (raw)
In-Reply-To: <20140725110342.GD5269@arm.com>
On 07/25/2014 08:03 PM, Will Deacon wrote:
> On Fri, Jul 25, 2014 at 11:36:49AM +0100, AKASHI Takahiro wrote:
>> On 07/25/2014 12:01 AM, Andy Lutomirski wrote:
>>>>> If so, then you risk (at least) introducing
>>>>>
>>>>> a nice user-triggerable OOPS if audit is enabled.
>>>>
>>>>
>>>> Can you please elaborate this?
>>>> Since I didn't find any definition of audit's behavior when syscall is
>>>> rewritten to -1, I thought it is reasonable to skip "exit tracing" of
>>>> "skipped" syscall.
>>>> (otherwise, "fake" seems to be more appropriate :)
>>>
>>> The audit entry hook will oops if you call it twice in a row without
>>> calling the exit hook in between.
>>
>> Thank you, I could reproduce this problem which hits BUG(in_syscall) in
>> audit_syscall_entry(). Really bad, and I fixed it in my next version and
>> now a "skipped" system call is also traced by audit.
>
> Can you reproduce this on arch/arm/ too? If so, we should also fix the code
> there.
As far as I tried on arm with syscall auditing enabled,
1) Changing a syscall number to -1 under seccomp doesn't hit BUG_ON(in_syscall).
2) But, in fact, audit_syscall_entry() is NOT called in this case because
__secure_computing() returns -1 and then it causes the succeeding tracing
in syscall_trace_enter(), including audit_syscall_entry(), skipped.
3) On the other hand, calling syscall(-1) from userspace hits BUG_ON because
the return path, ret_slow_syscall, doesn't contain syscall_trace_exit().
4) When we re-write a syscall number to -1 without seccomp, we will also see
BUG_ON hit, although I didn't try yet.
Fixing case 3 is easy, but should we also fix case 2?
Please note that, even if we call audit_syscall_exit() in case 2 or 3, no log against
syscall -1 will be recorded because audit_filter_syscall() doesn't allow logging
for any syscall number which is greater than 2048.
This behavior was introduced by Andy's patch, a3c54931, in v3.16-rc.
If the intention of "-1" is to fake a system call, this behavior seems to be a bit odd.
Thanks,
-Takahiro AKASHI
> Will
>
next prev parent reply other threads:[~2014-07-29 6:49 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-22 9:14 [PATCH v5 0/3] arm64: Add seccomp support AKASHI Takahiro
2014-07-22 9:14 ` [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations AKASHI Takahiro
2014-07-22 20:15 ` Kees Cook
2014-07-23 7:03 ` AKASHI Takahiro
2014-07-23 8:25 ` Will Deacon
2014-07-23 9:09 ` AKASHI Takahiro
2014-07-23 15:13 ` Kees Cook
2014-07-24 3:54 ` Andy Lutomirski
2014-07-24 5:57 ` AKASHI Takahiro
2014-07-24 15:01 ` Andy Lutomirski
2014-07-25 10:36 ` AKASHI Takahiro
2014-07-25 11:03 ` Will Deacon
2014-07-29 6:49 ` AKASHI Takahiro [this message]
2014-07-29 13:26 ` Will Deacon
2014-07-22 9:14 ` [PATCH v5 2/3] asm-generic: Add generic seccomp.h for secure computing mode 1 AKASHI Takahiro
2014-07-24 3:40 ` Andy Lutomirski
2014-07-24 4:41 ` Kees Cook
2014-07-24 5:17 ` AKASHI Takahiro
2014-07-24 14:57 ` Andy Lutomirski
2014-07-25 8:52 ` AKASHI Takahiro
2014-07-22 9:14 ` [PATCH v5 3/3] arm64: Add seccomp support AKASHI Takahiro
2014-07-24 3:52 ` Andy Lutomirski
2014-07-24 5:40 ` AKASHI Takahiro
2014-07-24 15:00 ` Andy Lutomirski
2014-07-24 15:16 ` Catalin Marinas
2014-07-25 9:37 ` AKASHI Takahiro
2014-08-05 15:08 ` Kees Cook
2014-08-08 7:35 ` AKASHI Takahiro
2014-08-11 9:24 ` Will Deacon
2014-08-12 6:57 ` AKASHI Takahiro
2014-08-12 9:40 ` Will Deacon
2014-08-12 11:17 ` AKASHI Takahiro
2014-08-15 14:33 ` Will Deacon
2014-07-22 20:16 ` [PATCH v5 0/3] " Kees Cook
2014-07-23 7:09 ` AKASHI Takahiro
2014-07-23 15:36 ` Kees Cook
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