RFC: selinux avc trace
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Message ID 80a23580-5067-93b0-53fa-3bd53253c056@sony.com
State Superseded
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  • RFC: selinux avc trace
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peter enderborg July 30, 2020, 2:29 p.m. UTC
I did manage to rebase it but this is about my approach.

Compared to Thiébaud Weksteen patch this adds:

1 Filtering. Types goes to trace so we can put up a filter for contexts or type etc.

2 It tries also to cover non denies.  And upon that you should be able to do coverage tools.
I think many systems have a lot more rules that what is needed, but there is good way
to find out what.  A other way us to make a stat page for the rules, but this way connect to
userspace and can be used for test cases.

This code need a lot more work, but it shows how the filter should work (extra info is not right)
and there are  memory leaks, extra debug info and nonsense variable etc.

From: Peter Enderborg <peter.enderborg@sony.com>
Date: Thu, 30 Jul 2020 14:44:53 +0200
Subject: [PATCH] RFC: selinux avc trace

This is not done yet. But it shows a trace for selinux avc.
---
 include/trace/events/avc.h |  92 +++++++++++++++++++++++++++++
 security/selinux/avc.c     | 115 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 205 insertions(+), 2 deletions(-)
 create mode 100644 include/trace/events/avc.h

Comments

Stephen Smalley July 30, 2020, 2:50 p.m. UTC | #1
On Thu, Jul 30, 2020 at 10:29 AM peter enderborg
<peter.enderborg@sony.com> wrote:
>
> I did manage to rebase it but this is about my approach.
>
> Compared to Thiébaud Weksteen patch this adds:
>
> 1 Filtering. Types goes to trace so we can put up a filter for contexts or type etc.
>
> 2 It tries also to cover non denies.  And upon that you should be able to do coverage tools.
> I think many systems have a lot more rules that what is needed, but there is good way
> to find out what.  A other way us to make a stat page for the rules, but this way connect to
> userspace and can be used for test cases.
>
> This code need a lot more work, but it shows how the filter should work (extra info is not right)
> and there are  memory leaks, extra debug info and nonsense variable etc.

Perhaps the two of you could work together to come up with a common
tracepoint that addresses both needs.
On the one hand, we don't need/want to duplicate the avc message
itself; we just need enough to be able to correlate them.
With respect to non-denials, SELinux auditallow statements can be used
to generate avc: granted messages that can be used to support coverage
tools although you can easily flood the logs that way.  One other
limitation of the other patch is that it doesn't support generating
trace information for denials silenced by dontaudit rules, which might
be challenging to debug especially on Android where you can't just run
semodule -DB to strip all dontaudits.
Steven Rostedt July 30, 2020, 3:04 p.m. UTC | #2
On Thu, 30 Jul 2020 16:29:12 +0200
peter enderborg <peter.enderborg@sony.com> wrote:

> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM avc
> +
> +#if !defined(_TRACE_AVC_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_AVC_H
> +
> +#include <linux/tracepoint.h>
> +TRACE_EVENT(avc_data,
> +        TP_PROTO(u32 requested,
> +             u32 denied,
> +             u32 audited,
> +             int result,
> +             const char *msg
> +             ),
> +
> +        TP_ARGS(requested, denied, audited, result,msg),
> +
> +        TP_STRUCT__entry(
> +             __field(u32, requested)
> +             __field(u32, denied)
> +             __field(u32, audited)
> +             __field(int, result)
> +             __array(char, msg, 255)

You want to use __string() here, otherwise you are wasting a lot of
buffer space.

		__string( msg, msg)

> +                 ),
> +
> +        TP_fast_assign(
> +               __entry->requested    = requested;
> +               __entry->denied    = denied;
> +               __entry->audited    = audited;
> +               __entry->result    = result;
> +               memcpy(__entry->msg, msg, 255);

Not to mention, the above is a bug. As the msg being passed in, is
highly unlikely to be 255 bytes. You just leaked all that memory after
the sting to user space.

Where you want here:

		__assign_str( msg, msg );


-- Steve



> +    ),
> +
> +        TP_printk("requested=0x%x denied=%d audited=%d result=%d
> msg=%s",
> +              __entry->requested, __entry->denied, __entry->audited,
> __entry->result, __entry->msg
> +              )
peter enderborg July 30, 2020, 3:31 p.m. UTC | #3
On 7/30/20 5:04 PM, Steven Rostedt wrote:
> On Thu, 30 Jul 2020 16:29:12 +0200
> peter enderborg <peter.enderborg@sony.com> wrote:
>
>> +#undef TRACE_SYSTEM
>> +#define TRACE_SYSTEM avc
>> +
>> +#if !defined(_TRACE_AVC_H) || defined(TRACE_HEADER_MULTI_READ)
>> +#define _TRACE_AVC_H
>> +
>> +#include <linux/tracepoint.h>
>> +TRACE_EVENT(avc_data,
>> +        TP_PROTO(u32 requested,
>> +             u32 denied,
>> +             u32 audited,
>> +             int result,
>> +             const char *msg
>> +             ),
>> +
>> +        TP_ARGS(requested, denied, audited, result,msg),
>> +
>> +        TP_STRUCT__entry(
>> +             __field(u32, requested)
>> +             __field(u32, denied)
>> +             __field(u32, audited)
>> +             __field(int, result)
>> +             __array(char, msg, 255)
> You want to use __string() here, otherwise you are wasting a lot of
> buffer space.
>
> 		__string( msg, msg)
It should be a full structure with a lot of sub strings.  But that make is even more relevant.
>
>> +                 ),
>> +
>> +        TP_fast_assign(
>> +               __entry->requested    = requested;
>> +               __entry->denied    = denied;
>> +               __entry->audited    = audited;
>> +               __entry->result    = result;
>> +               memcpy(__entry->msg, msg, 255);
> Not to mention, the above is a bug. As the msg being passed in, is
> highly unlikely to be 255 bytes. You just leaked all that memory after
> the sting to user space.
>
> Where you want here:
>
> 		__assign_str( msg, msg );

Directly in to the code. Was more in to get in to discussion on how complex we should have
the trace data. There is a lot of fields. Not all is always present. Is there any good way
to handle that? Like "something= somethingelse=42" or "something=nil somthingelse=42"


>
> -- Steve
>
>
>
>> +    ),
>> +
>> +        TP_printk("requested=0x%x denied=%d audited=%d result=%d
>> msg=%s",
>> +              __entry->requested, __entry->denied, __entry->audited,
>> __entry->result, __entry->msg
>> +              )
peter enderborg July 30, 2020, 3:47 p.m. UTC | #4
On 7/30/20 4:50 PM, Stephen Smalley wrote:
> On Thu, Jul 30, 2020 at 10:29 AM peter enderborg
> <peter.enderborg@sony.com> wrote:
>> I did manage to rebase it but this is about my approach.
>>
>> Compared to Thiébaud Weksteen patch this adds:
>>
>> 1 Filtering. Types goes to trace so we can put up a filter for contexts or type etc.
>>
>> 2 It tries also to cover non denies.  And upon that you should be able to do coverage tools.
>> I think many systems have a lot more rules that what is needed, but there is good way
>> to find out what.  A other way us to make a stat page for the rules, but this way connect to
>> userspace and can be used for test cases.
>>
>> This code need a lot more work, but it shows how the filter should work (extra info is not right)
>> and there are  memory leaks, extra debug info and nonsense variable etc.
> Perhaps the two of you could work together to come up with a common
> tracepoint that addresses both needs.

Sounds good to me.

> On the one hand, we don't need/want to duplicate the avc message
> itself; we just need enough to be able to correlate them.
> With respect to non-denials, SELinux auditallow statements can be used
> to generate avc: granted messages that can be used to support coverage
> tools although you can easily flood the logs that way.  One other

That is one reason to use trace. I can be used for things that
generate a lot of data. Like memory allocations and scheduler etc,
and it is a developer tool so you should not have to worry about DOS etc.

Both netlink and android logging are too happy to throw away data for
developers to be happy.

> limitation of the other patch is that it doesn't support generating
> trace information for denials silenced by dontaudit rules, which might
> be challenging to debug especially on Android where you can't just run
> semodule -DB to strip all dontaudits.

I think that only work for rooted devices. Many application developers
run on commercial devices that are locked, but they do have access
to trace. But I have no idea if they (google) have intended the selinux traces to
available there.
Steven Rostedt July 30, 2020, 4:02 p.m. UTC | #5
On Thu, 30 Jul 2020 17:31:17 +0200
peter enderborg <peter.enderborg@sony.com> wrote:

> On 7/30/20 5:04 PM, Steven Rostedt wrote:
> > On Thu, 30 Jul 2020 16:29:12 +0200
> > peter enderborg <peter.enderborg@sony.com> wrote:
> >  
> >> +#undef TRACE_SYSTEM
> >> +#define TRACE_SYSTEM avc
> >> +
> >> +#if !defined(_TRACE_AVC_H) || defined(TRACE_HEADER_MULTI_READ)
> >> +#define _TRACE_AVC_H
> >> +
> >> +#include <linux/tracepoint.h>
> >> +TRACE_EVENT(avc_data,
> >> +        TP_PROTO(u32 requested,
> >> +             u32 denied,
> >> +             u32 audited,
> >> +             int result,
> >> +             const char *msg
> >> +             ),
> >> +
> >> +        TP_ARGS(requested, denied, audited, result,msg),
> >> +
> >> +        TP_STRUCT__entry(
> >> +             __field(u32, requested)
> >> +             __field(u32, denied)
> >> +             __field(u32, audited)
> >> +             __field(int, result)
> >> +             __array(char, msg, 255)  
> > You want to use __string() here, otherwise you are wasting a lot of
> > buffer space.
> >
> > 		__string( msg, msg)  

> It should be a full structure with a lot of sub strings.  But that make is even more relevant.

So one event instance can have a list of strings recorded?

> >  
> >> +                 ),
> >> +
> >> +        TP_fast_assign(
> >> +               __entry->requested    = requested;
> >> +               __entry->denied    = denied;
> >> +               __entry->audited    = audited;
> >> +               __entry->result    = result;
> >> +               memcpy(__entry->msg, msg, 255);  
> > Not to mention, the above is a bug. As the msg being passed in, is
> > highly unlikely to be 255 bytes. You just leaked all that memory after
> > the sting to user space.
> >
> > Where you want here:
> >
> > 		__assign_str( msg, msg );  
> 
> Directly in to the code. Was more in to get in to discussion on how complex we should have
> the trace data. There is a lot of fields. Not all is always present. Is there any good way
> to handle that? Like "something= somethingelse=42" or "something=nil somthingelse=42"

Can you show what you want to record and what you want to display? I'm
not totally understanding the request.

-- Steve

> >> +    ),
> >> +
> >> +        TP_printk("requested=0x%x denied=%d audited=%d result=%d
> >> msg=%s",
> >> +              __entry->requested, __entry->denied, __entry->audited,
> >> __entry->result, __entry->msg
> >> +              )  
>
peter enderborg July 30, 2020, 5:05 p.m. UTC | #6
On 7/30/20 6:02 PM, Steven Rostedt wrote:
> On Thu, 30 Jul 2020 17:31:17 +0200
> peter enderborg <peter.enderborg@sony.com> wrote:
>
>> On 7/30/20 5:04 PM, Steven Rostedt wrote:
>>> On Thu, 30 Jul 2020 16:29:12 +0200
>>> peter enderborg <peter.enderborg@sony.com> wrote:
>>>  
>>>> +#undef TRACE_SYSTEM
>>>> +#define TRACE_SYSTEM avc
>>>> +
>>>> +#if !defined(_TRACE_AVC_H) || defined(TRACE_HEADER_MULTI_READ)
>>>> +#define _TRACE_AVC_H
>>>> +
>>>> +#include <linux/tracepoint.h>
>>>> +TRACE_EVENT(avc_data,
>>>> +        TP_PROTO(u32 requested,
>>>> +             u32 denied,
>>>> +             u32 audited,
>>>> +             int result,
>>>> +             const char *msg
>>>> +             ),
>>>> +
>>>> +        TP_ARGS(requested, denied, audited, result,msg),
>>>> +
>>>> +        TP_STRUCT__entry(
>>>> +             __field(u32, requested)
>>>> +             __field(u32, denied)
>>>> +             __field(u32, audited)
>>>> +             __field(int, result)
>>>> +             __array(char, msg, 255)  
>>> You want to use __string() here, otherwise you are wasting a lot of
>>> buffer space.
>>>
>>> 		__string( msg, msg)  
>> It should be a full structure with a lot of sub strings.  But that make is even more relevant.
> So one event instance can have a list of strings recorded?

Yes, it is a list very similar to a normal trace. But it is more generic.

For example ino= is for filesystems that have inode, but for a
violation that send a signal that make no sense at all.  Network
addresses is in many cases not applicable. laddr= is only exist for
for IP.

So if you just print them it will look like:

avc:  denied  { find } for interface=vendor.qti.hardware.perf::IPerf sid=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 pid=9164 scontext=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 tcontext=u:object_r:vendor_hal_perf_hwservice:s0 tclass=hwservice_manager permissive=0
 avc:  denied  { execute } for  pid=13914 comm="ScionFrontendAp" path="/data/user_de/0/com.google.android.gms/app_chimera/m/00000002/oat/arm64/DynamiteLoader.odex" dev="sda77" ino=204967 scontext=u:r:platform_app:s0:c512,c768 tcontext=u:object_r:privapp_data_file:s0:c512,c768 tclass=file permissive=0 ppid=788 pcomm="main" pgid=13914 pgcomm="on.updatecenter"

It omit the fields that are not used. Some parts are common some are not. So a correct format specification for trace will be problematic if there is no "optional" field indicator.

>
>>>  
>>>> +                 ),
>>>> +
>>>> +        TP_fast_assign(
>>>> +               __entry->requested    = requested;
>>>> +               __entry->denied    = denied;
>>>> +               __entry->audited    = audited;
>>>> +               __entry->result    = result;
>>>> +               memcpy(__entry->msg, msg, 255);  
>>> Not to mention, the above is a bug. As the msg being passed in, is
>>> highly unlikely to be 255 bytes. You just leaked all that memory after
>>> the sting to user space.
>>>
>>> Where you want here:
>>>
>>> 		__assign_str( msg, msg );  
>> Directly in to the code. Was more in to get in to discussion on how complex we should have
>> the trace data. There is a lot of fields. Not all is always present. Is there any good way
>> to handle that? Like "something= somethingelse=42" or "something=nil somthingelse=42"
> Can you show what you want to record and what you want to display? I'm
> not totally understanding the request.
>
> -- Steve
>
>>>> +    ),
>>>> +
>>>> +        TP_printk("requested=0x%x denied=%d audited=%d result=%d
>>>> msg=%s",
>>>> +              __entry->requested, __entry->denied, __entry->audited,
>>>> __entry->result, __entry->msg
>>>> +              )
Steven Rostedt July 30, 2020, 5:16 p.m. UTC | #7
On Thu, 30 Jul 2020 19:05:49 +0200
peter enderborg <peter.enderborg@sony.com> wrote:

> >> It should be a full structure with a lot of sub strings.  But that make is even more relevant.  
> > So one event instance can have a list of strings recorded?  
> 
> Yes, it is a list very similar to a normal trace. But it is more generic.
> 
> For example ino= is for filesystems that have inode, but for a
> violation that send a signal that make no sense at all.  Network
> addresses is in many cases not applicable. laddr= is only exist for
> for IP.
> 
> So if you just print them it will look like:
> 
> avc:  denied  { find } for interface=vendor.qti.hardware.perf::IPerf sid=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 pid=9164 scontext=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 tcontext=u:object_r:vendor_hal_perf_hwservice:s0 tclass=hwservice_manager permissive=0
>  avc:  denied  { execute } for  pid=13914 comm="ScionFrontendAp" path="/data/user_de/0/com.google.android.gms/app_chimera/m/00000002/oat/arm64/DynamiteLoader.odex" dev="sda77" ino=204967 scontext=u:r:platform_app:s0:c512,c768 tcontext=u:object_r:privapp_data_file:s0:c512,c768 tclass=file permissive=0 ppid=788 pcomm="main" pgid=13914 pgcomm="on.updatecenter"
> 
> It omit the fields that are not used. Some parts are common some are not. So a correct format specification for trace will be problematic if there is no "optional" field indicator.

That's all quite noisy. What is the object of these changes? What
exactly are you trying to trace and why?

-- Steve
peter enderborg July 30, 2020, 7:12 p.m. UTC | #8
On 7/30/20 7:16 PM, Steven Rostedt wrote:
> On Thu, 30 Jul 2020 19:05:49 +0200
> peter enderborg <peter.enderborg@sony.com> wrote:
>
>>>> It should be a full structure with a lot of sub strings.  But that make is even more relevant.  
>>> So one event instance can have a list of strings recorded?  
>> Yes, it is a list very similar to a normal trace. But it is more generic.
>>
>> For example ino= is for filesystems that have inode, but for a
>> violation that send a signal that make no sense at all.  Network
>> addresses is in many cases not applicable. laddr= is only exist for
>> for IP.
>>
>> So if you just print them it will look like:
>>
>> avc:  denied  { find } for interface=vendor.qti.hardware.perf::IPerf sid=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 pid=9164 scontext=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 tcontext=u:object_r:vendor_hal_perf_hwservice:s0 tclass=hwservice_manager permissive=0
>>  avc:  denied  { execute } for  pid=13914 comm="ScionFrontendAp" path="/data/user_de/0/com.google.android.gms/app_chimera/m/00000002/oat/arm64/DynamiteLoader.odex" dev="sda77" ino=204967 scontext=u:r:platform_app:s0:c512,c768 tcontext=u:object_r:privapp_data_file:s0:c512,c768 tclass=file permissive=0 ppid=788 pcomm="main" pgid=13914 pgcomm="on.updatecenter"
>>
>> It omit the fields that are not used. Some parts are common some are not. So a correct format specification for trace will be problematic if there is no "optional" field indicator.
> That's all quite noisy. What is the object of these changes? What
> exactly are you trying to trace and why?

It is noisy, and it have to be. it covers a lot of different areas.  One common problem is
to debug userspace applications regarding violations. You get the violation from the logs
and try to figure out what you did to cause it. With a trace point you can do much better
when combine with other traces. Having a the userspace stack is a very good way,
unfortunately  it does not work on that many architectures within trace.

What exactly are you doing with any trace? You collect data to analyse what's
going on. This is not different. Selinux do a specific thing, but is has lots of parameters.


> -- Steve
Steven Rostedt July 30, 2020, 7:29 p.m. UTC | #9
On Thu, 30 Jul 2020 21:12:39 +0200
peter enderborg <peter.enderborg@sony.com> wrote:

> >> avc:  denied  { find } for interface=vendor.qti.hardware.perf::IPerf sid=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 pid=9164 scontext=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 tcontext=u:object_r:vendor_hal_perf_hwservice:s0 tclass=hwservice_manager permissive=0
> >>  avc:  denied  { execute } for  pid=13914 comm="ScionFrontendAp" path="/data/user_de/0/com.google.android.gms/app_chimera/m/00000002/oat/arm64/DynamiteLoader.odex" dev="sda77" ino=204967 scontext=u:r:platform_app:s0:c512,c768 tcontext=u:object_r:privapp_data_file:s0:c512,c768 tclass=file permissive=0 ppid=788 pcomm="main" pgid=13914 pgcomm="on.updatecenter"
> >>
> >> It omit the fields that are not used. Some parts are common some are not. So a correct format specification for trace will be problematic if there is no "optional" field indicator.  
> > That's all quite noisy. What is the object of these changes? What
> > exactly are you trying to trace and why?  
> 
> It is noisy, and it have to be. it covers a lot of different areas.  One common problem is
> to debug userspace applications regarding violations. You get the violation from the logs
> and try to figure out what you did to cause it. With a trace point you can do much better
> when combine with other traces. Having a the userspace stack is a very good way,
> unfortunately  it does not work on that many architectures within trace.
> 
> What exactly are you doing with any trace? You collect data to analyse what's
> going on. This is not different. Selinux do a specific thing, but is has lots of parameters.

Have you thought of adding multiple trace events with if statements
around them to decode each specific type of event?

Note, you can have a generic event that gets enabled by all the other
events via the "reg" and "unreg" part of TRACE_EVENT_FN(). Say its
called trace_avc, make a dummy trace_avc() call hat doesn't even need
to be called anywhere, it just needs to exist to get to the other trace
events.

Then have:

	if (trace_avc_enabled()) {
		if (event1)
			trace_avc_req_event1();
		if (event2)
			trace_avc_req_event2();
		[..]
	}

The reason for the trace_avc_enabled() is because that's a static
branch, which is a nop when not enabled. When enabled, it is a jump to
the out of band if condition block that has all the other trace events.

-- Steve
peter enderborg July 30, 2020, 7:50 p.m. UTC | #10
On 7/30/20 9:29 PM, Steven Rostedt wrote:
> On Thu, 30 Jul 2020 21:12:39 +0200
> peter enderborg <peter.enderborg@sony.com> wrote:
>
>>>> avc:  denied  { find } for interface=vendor.qti.hardware.perf::IPerf sid=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 pid=9164 scontext=u:r:permissioncontroller_app:s0:c230,c256,c512,c768 tcontext=u:object_r:vendor_hal_perf_hwservice:s0 tclass=hwservice_manager permissive=0
>>>>  avc:  denied  { execute } for  pid=13914 comm="ScionFrontendAp" path="/data/user_de/0/com.google.android.gms/app_chimera/m/00000002/oat/arm64/DynamiteLoader.odex" dev="sda77" ino=204967 scontext=u:r:platform_app:s0:c512,c768 tcontext=u:object_r:privapp_data_file:s0:c512,c768 tclass=file permissive=0 ppid=788 pcomm="main" pgid=13914 pgcomm="on.updatecenter"
>>>>
>>>> It omit the fields that are not used. Some parts are common some are not. So a correct format specification for trace will be problematic if there is no "optional" field indicator.  
>>> That's all quite noisy. What is the object of these changes? What
>>> exactly are you trying to trace and why?  
>> It is noisy, and it have to be. it covers a lot of different areas.  One common problem is
>> to debug userspace applications regarding violations. You get the violation from the logs
>> and try to figure out what you did to cause it. With a trace point you can do much better
>> when combine with other traces. Having a the userspace stack is a very good way,
>> unfortunately  it does not work on that many architectures within trace.
>>
>> What exactly are you doing with any trace? You collect data to analyse what's
>> going on. This is not different. Selinux do a specific thing, but is has lots of parameters.
> Have you thought of adding multiple trace events with if statements
> around them to decode each specific type of event?

Yes. And I think class is good split point. But I think it will require
a few layers, but a is mostly data driven so I think it might be hard
to do it compile time.  I think a hybrid might be possible,
but it then we need some ugly part with a other separator than =,
or some escape seq to separate.

sort of "generc1=X generic2=Y variable1^x variable2^y" or

"generc1=X generic2=Y leftover=[variable1=x variable2=y]"

If there was a formal parameter tree we could maybe do some
generated printer. I don't think there are one, maybe Paul Moore or Stephen Smalley
can verify that.

 

> Note, you can have a generic event that gets enabled by all the other
> events via the "reg" and "unreg" part of TRACE_EVENT_FN(). Say its
> called trace_avc, make a dummy trace_avc() call hat doesn't even need
> to be called anywhere, it just needs to exist to get to the other trace
> events.
>
> Then have:
>
> 	if (trace_avc_enabled()) {
> 		if (event1)
> 			trace_avc_req_event1();
> 		if (event2)
> 			trace_avc_req_event2();
> 		[..]
> 	}
>
> The reason for the trace_avc_enabled() is because that's a static
> branch, which is a nop when not enabled. When enabled, it is a jump to
> the out of band if condition block that has all the other trace events.
>
> -- Steve
Thiébaud Weksteen July 31, 2020, 11:07 a.m. UTC | #11
Thanks Peter, this looks like a great start.

> Perhaps the two of you could work together to come up with a common
tracepoint that addresses both needs.

Agreed.

> 1 Filtering. Types goes to trace so we can put up a filter for contexts or type etc.

That's right. I think this is the main reason why we would need
further attributes in the trace event.

> 2 It tries also to cover non denies.  And upon that you should be able to do coverage tools.
> I think many systems have a lot more rules that what is needed, but there is good way
> to find out what.  A other way us to make a stat page for the rules, but this way connect to
> userspace and can be used for test cases.

This is a great idea too.

>> On the one hand, we don't need/want to duplicate the avc message
>> itself; we just need enough to be able to correlate them.
>> With respect to non-denials, SELinux auditallow statements can be used
>> to generate avc: granted messages that can be used to support coverage
>> tools although you can easily flood the logs that way.  One other
> That is one reason to use trace.

Yes, that's right. I don't have any concern about the flooding here.
As Peter mentioned, trace is specially designed for this purpose.

On the patch, few things to note:

> ---
> +#include <linux/tracepoint.h>
> +TRACE_EVENT(avc_data,
> +        TP_PROTO(u32 requested,
> +             u32 denied,
> +             u32 audited,
> +             int result,
> +             const char *msg
> +             ),

I would not store the raw msg from avc. As we discussed, it is useful
to be able to match against the values we are seeing in the avc denial
message but these attributes should be simple (as opposed to
composite) so the filtering can easily be setup (see section 5.1 in
https://www.kernel.org/doc/Documentation/trace/events.txt). It makes
more sense extracting scontext and tcontext (for instance) which
allows for a precise filtering setup.

Here, I would also pass down the "struct selinux_audit_data" to avoid
a large list of arguments.

> +TRACE_EVENT(avc_req,
> +        TP_PROTO(u32 requested,
> +             u32 denied,
> +             u32 audited,
> +             int result,
> +             const char *msg,
> +             u32 ssid,
> +             struct selinux_state *state
> +             ),

I don't see that event being used later on. What was the intention here?

> +static int avc_dump_querys(struct selinux_state *state, char *ab, u32 ssid, u32 tsid, u16 tclass)
> +{
> +    int rc;
> +    char *scontext;
> +    u32 scontext_len;
> +    int rp;
> +
> +    rc = security_sid_to_context(state,ssid, &scontext, &scontext_len);
> +    if (rc)
> +        rp = sprintf(ab, "ssid=%d", ssid);
> +    else {
> +        rp = sprintf(ab, "scontext=%s", scontext);
> +        kfree(scontext);
> +    }
> +
> +    rc = security_sid_to_context(state, tsid, &scontext, &scontext_len);
> +    if (rc)
> +        rp +=sprintf(ab+rp, " tsid=%d", tsid);
> +    else {
> +        rp +=sprintf(ab+rp, " tcontext=%s", scontext);
> +        kfree(scontext);
> +    }
> +
> +    BUG_ON(!tclass || tclass >= ARRAY_SIZE(secclass_map));
> +    rp += sprintf(ab+rp, " tclass=%s", secclass_map[tclass-1].name);
> +    return rp;
> +}

As I mentioned before, this is literally repeating the avc audit
message. We are better off storing the exact fields we are interested
in, so that the filtering is precise.

Thanks

Patch
diff mbox series

diff --git a/include/trace/events/avc.h b/include/trace/events/avc.h
new file mode 100644
index 000000000000..28c1044e918b
--- /dev/null
+++ b/include/trace/events/avc.h
@@ -0,0 +1,92 @@ 
+/*
+ * License terms: GNU General Public License (GPL) version 2
+ *
+ * Author: Peter Enderborg <Peter.Enderborg@sony.com>
+ */
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM avc
+
+#if !defined(_TRACE_AVC_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_AVC_H
+
+#include <linux/tracepoint.h>
+TRACE_EVENT(avc_data,
+        TP_PROTO(u32 requested,
+             u32 denied,
+             u32 audited,
+             int result,
+             const char *msg
+             ),
+
+        TP_ARGS(requested, denied, audited, result,msg),
+
+        TP_STRUCT__entry(
+             __field(u32, requested)
+             __field(u32, denied)
+             __field(u32, audited)
+             __field(int, result)
+             __array(char, msg, 255)
+                 ),
+
+        TP_fast_assign(
+               __entry->requested    = requested;
+               __entry->denied    = denied;
+               __entry->audited    = audited;
+               __entry->result    = result;
+               memcpy(__entry->msg, msg, 255);
+    ),
+
+        TP_printk("requested=0x%x denied=%d audited=%d result=%d msg=%s",
+              __entry->requested, __entry->denied, __entry->audited, __entry->result, __entry->msg
+              )
+);
+TRACE_EVENT(avc_req,
+        TP_PROTO(u32 requested,
+             u32 denied,
+             u32 audited,
+             int result,
+             const char *msg,
+             u32 ssid,
+             struct selinux_state *state
+             ),
+
+        TP_ARGS(requested, denied, audited, result,msg, ssid, state),
+
+        TP_STRUCT__entry(
+            __field(u32, requested)
+            __field(u32, denied)
+            __field(u32, audited)
+            __field(int, result)
+            __array(char, msg, 255)
+            __field(u32, ssid)
+            __field(struct selinux_state *, state)
+            __field(char*, scontext)
+            __field(u32, ssid_len)
+            __field(u32, ssid_res)
+                 ),
+
+        TP_fast_assign(
+            __entry->requested    = requested;
+            __entry->denied    = denied;
+            __entry->audited    = audited;
+             __entry->result    = result;
+            memcpy(__entry->msg, msg, 255);
+            __entry->ssid    = ssid;
+            __entry->state    = state;
+            __entry->ssid_res = security_sid_to_context(
+                           state,
+                           ssid,
+                           &__entry->scontext,
+                           &__entry->ssid_len);
+    ),
+
+        TP_printk("requested=0x%x denied=%d audited=%d result=%d msg=%s ssid=%d state=%p scontext=%s slen=%d s=%d",
+              __entry->requested, __entry->denied, __entry->audited, __entry->result, __entry->msg, __entry->ssid, __entry->state,__entry->scontext,__entry->ssid_len, __entry->ssid_res
+              )
+);
+
+#endif /* _TRACE_AVC_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index d18cb32a242a..d8cb9a23d669 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -30,6 +30,8 @@ 
 #include "avc.h"
 #include "avc_ss.h"
 #include "classmap.h"
+#define CREATE_TRACE_POINTS
+#include <trace/events/avc.h>
 
 #define AVC_CACHE_SLOTS            512
 #define AVC_DEF_CACHE_THRESHOLD        512
@@ -126,6 +128,41 @@  static inline int avc_hash(u32 ssid, u32 tsid, u16 tclass)
     return (ssid ^ (tsid<<2) ^ (tclass<<4)) & (AVC_CACHE_SLOTS - 1);
 }
 
+static int avc_dump_avs(char *ab, u16 tclass, u32 av)
+{
+    const char **perms;
+    int i, perm;
+    int rp;
+
+    if (av == 0) {
+        rp = sprintf(ab, " null");
+        return rp;
+    }
+
+    BUG_ON(!tclass || tclass >= ARRAY_SIZE(secclass_map));
+    perms = secclass_map[tclass-1].perms;
+
+    rp = sprintf(ab, " {");
+    i = 0;
+    perm = 1;
+    while (i < (sizeof(av) * 8)) {
+        if ((perm & av) && perms[i]) {
+            rp +=sprintf(ab+rp, " %s", perms[i]);
+            av &= ~perm;
+        }
+        i++;
+        perm <<= 1;
+    }
+
+    if (av)
+        rp += sprintf(ab+rp, " 0x%x", av);
+
+    rp +=sprintf(ab+rp, " }");
+    return rp;
+}
+
+
+
 /**
  * avc_init - Initialize the AVC.
  *
@@ -421,8 +458,12 @@  static inline int avc_xperms_audit(struct selinux_state *state,
 
     audited = avc_xperms_audit_required(
             requested, avd, xpd, perm, result, &denied);
-    if (likely(!audited))
+    if (likely(!audited)) {
+        trace_avc_data(requested, denied, audited, -1,"foo");
         return 0;
+    }
+
+    trace_avc_data(requested, denied, audited, -1,"bar");
     return slow_avc_audit(state, ssid, tsid, tclass, requested,
             audited, denied, result, ad);
 }
@@ -541,6 +582,34 @@  static inline struct avc_node *avc_search_node(struct selinux_avc *avc,
     return ret;
 }
 
+static int avc_dump_querys(struct selinux_state *state, char *ab, u32 ssid, u32 tsid, u16 tclass)
+{
+    int rc;
+    char *scontext;
+    u32 scontext_len;
+    int rp;
+
+    rc = security_sid_to_context(state,ssid, &scontext, &scontext_len);
+    if (rc)
+        rp = sprintf(ab, "ssid=%d", ssid);
+    else {
+        rp = sprintf(ab, "scontext=%s", scontext);
+        kfree(scontext);
+    }
+
+    rc = security_sid_to_context(state, tsid, &scontext, &scontext_len);
+    if (rc)
+        rp +=sprintf(ab+rp, " tsid=%d", tsid);
+    else {
+        rp +=sprintf(ab+rp, " tcontext=%s", scontext);
+        kfree(scontext);
+    }
+
+    BUG_ON(!tclass || tclass >= ARRAY_SIZE(secclass_map));
+    rp += sprintf(ab+rp, " tclass=%s", secclass_map[tclass-1].name);
+    return rp;
+}
+
 /**
  * avc_lookup - Look up an AVC entry.
  * @ssid: source security identifier
@@ -690,6 +759,7 @@  static void avc_audit_pre_callback(struct audit_buffer *ab, void *a)
         audit_log_format(ab, " 0x%x", av);
 
     audit_log_format(ab, " } for ");
+
 }
 
 /**
@@ -780,6 +850,7 @@  noinline int slow_avc_audit(struct selinux_state *state,
     a->selinux_audit_data = &sad;
 
     common_lsm_audit(a, avc_audit_pre_callback, avc_audit_post_callback);
+    pr_info("done lsm");
     return 0;
 }
 
@@ -1105,6 +1176,34 @@  int avc_has_extended_perms(struct selinux_state *state,
         return rc2;
     return rc;
 }
+static int avc_dump_extra_info_s(char *ab,
+        struct common_audit_data *ad)
+{
+    struct task_struct *tsk = current;
+    int rp;
+
+    if (tsk && tsk->pid) {
+        rp = sprintf(ab, " ppid=%d pcomm=", tsk->parent->pid);
+        rp += sprintf(ab+rp, tsk->parent->comm);
+
+        if (tsk->group_leader->pid != tsk->pid) {
+            rp +=sprintf(ab+rp, " pgid=%d pgcomm=",
+                    tsk->group_leader->pid);
+            rp += sprintf(ab+rp,
+                    tsk->group_leader->comm);
+        } else if (tsk->parent->group_leader->pid) {
+            rp += sprintf(ab+rp, " pgid=%d pgcomm=",
+                    tsk->parent->group_leader->pid);
+            rp += sprintf(ab+rp,
+                    tsk->parent->group_leader->comm);
+        }
+    } else {
+        rp = sprintf(ab," no task %p", tsk);
+    }
+    return rp;
+}
+
+
 
 /**
  * avc_has_perm_noaudit - Check permissions but perform no auditing.
@@ -1178,14 +1277,26 @@  int avc_has_perm(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass,
 {
     struct av_decision avd;
     int rc, rc2;
+    char *lb;
+    int x;
+
+    lb = kmalloc(1024, GFP_KERNEL);
 
     rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested, 0,
                   &avd);
 
     rc2 = avc_audit(state, ssid, tsid, tclass, requested, &avd, rc,
             auditdata, 0);
-    if (rc2)
+    if (rc2)  {
+        kfree(lb);
         return rc2;
+    }
+
+    x = avc_dump_avs(lb, tclass, 42);
+    x += avc_dump_querys(state, lb+x,ssid, tsid, tclass);
+        if(1)    x += avc_dump_extra_info_s(lb+x, auditdata);
+    trace_avc_data(requested, rc, 0, rc2,lb);
+    kfree(lb);
     return rc;
 }